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Vitamin D deficiency is associated with the metabolic syndrome in morbid obesity
ARTICLE IN PRESS Clinical Nutrition (2007) 26, 573–580
Available at www.sciencedirect.com
http://intl.elsevierhealth.com/journals/clnu
ORIGINAL ARTICLE
Vitamin D deficiency is associated with the metabolic syndrome in morbid obesity$ Jose ´ I. Botella-Carreteroa,b,, Francisco Alvarez-Blascob, Juan J. Villafruelac, ´zqueza, He ´ctor F. Escobar-Morrealeb Jose ´ A. Balsaa, Clotilde Va a
Department of Clinical Nutrition, Hospital Ramo ´n y Cajal, 28034 Madrid, Spain Department of Endocrinology, Hospital Ramo ´n y Cajal, 28034 Madrid, Spain c Department of Nephrology, Hospital Ramo ´n y Cajal, 28034 Madrid, Spain b
Received 14 December 2006; accepted 24 May 2007
KEYWORDS Vitamin D; Metabolic syndrome; Obesity; Lipids; Insulin resistance
Summary Background & aims: Vitamin D deficiency has been recently associated with the metabolic syndrome. However, it is not known whether this possible association of vitamin D deficiency with the metabolic syndrome is still present at very high degrees of obesity, as in morbidly obese patients. Methods: Transversal, observational study that included 73 consecutive morbidly obese patients (body mass index X40 kg/m2). In every patient, anthropometric variables were recorded, fasting blood was assayed for 25-hydroxyvitamin D concentrations, lipid profiles, glucose and insulin levels, and insulin resistance was estimated by homeostasis model assessment. Results: Vitamin D deficiency was present in 37 of the 73 patients (50.7%). As defined by revised Adult Treatment Panel III criteria, 46 of the 73 obese patients (63%) had the metabolic syndrome. Vitamin D deficiency was more prevalent in morbidly obese patients presenting with the metabolic syndrome, compared with those who did not achieve the criteria for this syndrome (60.9% vs. 33.3% respectively, P ¼ 0.023). When serum concentrations of 25-hydroxyvitamin D were categorized in tertiles, there was an association of the prevalence of the metabolic syndrome with the former (P ¼ 0.038). Serum high-density lipoprotein cholesterol concentrations were lower (37.077.8 mg/dl vs. 44.978.7 mg/dl, P ¼ 0.003), and triglycerides levels were higher (163.3781.5 mg/dl vs. 95.1724.2 mg/dl, P ¼ 0.001) in the vitamin D-deficient group.
Abbreviations: BMI, body mass index; HDL, high density lipoprotein; LDL, low density lipoprotein; HOMA-IR, insulin resistance as determined by the homeostasis model assessment $ Conference presentation: Presented in part at the Press Conference of the Endocrine Society’s 88th Annual Meeting, Boston, 2006. Corresponding author. Department of Clinical Nutrition, Hospital Ramo ´n y Cajal, Carretera de Colmenar Km. 9.1, 28034 Madrid, Spain. Tel.: +34 91 336 8726; fax: +34 91 336 9029. E-mail address: [email protected] (J.I. Botella-Carretero). 0261-5614/$ - see front matter & 2007 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved. doi:10.1016/j.clnu.2007.05.009
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J.I. Botella-Carretero et al. Conclusion: Vitamin D deficiency is associated with the metabolic syndrome in morbidly obese patients. & 2007 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.
Introduction Obesity is a major public health problem in Western countries. The prevalence of obesity has significantly increased among these countries population over the past 30 years, and recent data estimate that nearly one-third of adults are obese.1,2 The impact of obesity on public health is profound, as it has been shown to be a major risk factor for cardiovascular disease3,4 and cancer,5 with a consequent reduction in life expectancy.6,7 Obesity is a major contributor to the constellation of cardiovascular disease risk factors associated with insulin resistance (glucose intolerance, dyslipidemia, hypertension, and central adiposity), commonly referred to as the metabolic syndrome.8 The metabolic syndrome has been estimated to affect more than 20% of adults in the United States,9 and it has been shown that its prevalence increases with worsening obesity.10,11 Vitamin D is known for the maintenance of mineral homeostasis and normal skeletal architecture. The precursor provitamin D, 7-dehydrocholesterol, absorbs ultraviolet radiation in the skin and is transformed into previtamin D3, which is rapidly converted to vitamin D3. The latter is metabolized in the liver to 25-hydroxyvitamin D3 and then in the kidney to its biologically active form 1,25-dihydroxyvitamin D3.12 Vitamin D also comes from diet in the form of vitamin D2 (ergocalciferol), mostly from fortified foods but also in small quantities from plant sources and irritated yeast, and in the form of vitamin D3 (cholecalciferol) from animal sources. Both vitamin D2 and vitamin D3 can be hydroxylated in the liver and later in the kidney, resulting in the biologically active form of vitamin D. Vitamin D deficiency, as determined by decreased serum concentrations of 25-hydroxyvitamin D,13,14 has become epidemic for all age groups in the United States and Europe.15,16 This occurs even in spite of fortification of certain foods, such as cereals and dairy products among others, with vitamin D.13 Besides, it has been shown that serum concentrations of 25-hydroxyvitamin D in people living in sun-rich environments where clothing or cultural practices do not prevent sun exposure, are much higher than in those with little sun exposure.17 Therefore, a reduction in sun exposure due to sunscreens, climate variations, clothing or cultural practices, together with inadequate ingestion of vitamin D through an ordinary diet, may produce vitamin D deficiency.14,17 Vitamin D deficiency not only causes metabolic bone disease, but may also increase the risk of other common chronic disorders.14 During the past few years, vitamin D deficiency has been linked to type 2 diabetes mellitus18,19 and cardiovascular risk.14,20 Furthermore, a possible role of vitamin D deficiency in the pathogenesis of the metabolic syndrome has been also recently suggested.21–23
Non-calcemic actions of vitamin D have been proposed to be responsible for these associations, because most cells and tissues in the body harbor the vitamin D receptor.24 Yet also, vitamin D deficiency is more prevalent in obese persons,25,26 and it has been proposed that this may result from accumulation of vitamin D in adipose tissue.27 As there is an inverse relationship between vitamin D levels and the degree of obesity,23 as well as with central adiposity,22 it has been difficult to distinguish the independent effects of obesity and vitamin D on metabolic syndrome. Furthermore, it is not known whether the association of vitamin D deficiency with the metabolic syndrome is still present at very high degrees of obesity, in which the possible effect of vitamin D status on the metabolic syndrome could be ameliorated or even completely overcome by the predominant effect of obesity. Therefore, we conducted this study to investigate the possible association of vitamin D status with the metabolic syndrome, its individual components, and insulin resistance in a cohort of morbidly obese patients. As it will be seen, given that the patients in our study with and without vitamin D deficiency had similar degree of obesity and waist circumference, the differences in metabolic syndrome prevalence and lipid levels found here may indeed reflect a true association between vitamin D status and the latter, irrespective of adiposity.
Patients and methods Subjects and study protocol Seventy-three consecutive morbidly obese patients (defined by a BMIX40 kg/m2) reporting to the Department of Clinical Nutrition of Hospital Ramo ´n y Cajal for bariatric surgery were recruited. All the subjects were Caucasian from European ancestry. Twenty-seven were on anti-hypertensive medication, seven were on blood glucose lowering drugs and/or insulin, and seven were on statins and/or fibrates. None of them were taking supplements of calcium and/or vitamin D, or any drug known to influence their concentrations aside from the aforementioned medication. None of the patients had intestinal malabsorption, nor inflammatory bowel disease. The ethics committee of the Hospital Ramo ´n y Cajal approved the protocol, and informed consent was obtained from each patient. Between 8 and 9 a.m. and after a 12-h overnight fast, an indwelling intravenous line was placed in a forearm vein and, after 15–30 min, basal blood samples were obtained in each patient. Body mass index, office blood pressure and waist to hip ratio were also recorded. All patients were evaluated before bariatric surgery. The diagnosis of the metabolic syndrome required the presence of three or more
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of the following criteria: abdominal obesity (waist circumference 4102 cm in men and 488 cm in women), triglycerides X150 mg/dl, high-density lipoprotein cholesterol (HDL) o40 mg/dl in men and o50 mg/dl in women, blood pressure X130/80 mmHg, fasting glucose X100 mg/dl, according to the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III28. Patients receiving pharmacological treatment for diabetes, hypertension or hypertriglyceridemia were considered as matching the corresponding criteria. In order to evaluate dietary patterns, we employed a food frequency questionnaire that has been previously validated in the Spanish population.29
Analytical procedures and reference ranges Lipid profiles including total cholesterol, low-density lipoprotein cholesterol (LDL), HDL, triglycerides and fasting glucose were analyzed using an Abbott Aeroset Automated Instrument Analyzer (Abbott Laboratories, Abbot Park, IL) with mean intra- and interassay coefficients of variation (CVs) below 2%. Fasting insulin was measured by immunochemiluminescence (Immulite 2000, Diagnostic Products Corporation, Los Angeles, CA) with mean CVs below 10%. Insulin resistance in the fasting state (HOMA-IR) was estimated from glucose and insulin concentrations using homeostasis model assessment.30 A commercial enzyme linked immunosorbent assay (ELISA) was employed for the measurement of 25-hydroxyvitamin D concentrations (IDS Ltd., Boldon, UK). The specificity of this assay is 100% for 25-hydroxyvitamin D3 and 75% for 25-hydroxyvitamin D2, and negligible cross-reactivity with vitamin D3 and vitamin D2 (o0.01% and o0.30%, respectively). The normal range for 25-hydroxyvitamin D plasma concentration was defined at our Institution by the 5th and 95th percentiles of a control group of 60 healthy blood donors, which were 20 and 60 ng/ml (50 and 150 nmol/l), respectively. This normal range is in accordance to the data reported from previous studies in sunny countries.31,32 However, as recent studies have proposed that levels equal to or above 32 ng/ml (80 nmol/l)17 are necessary for
maximal calcium absorption from the intestine,33 and to universally avoid secondary hyperparathyroidism,34,35 we defined vitamin D insufficiency as those levels between 20 and 32 ng/ml (50 and 80 nmol/l, respectively), and vitamin D deficiency as those below 20 ng/ml (50 nmol/l).36 Parathyroid hormone (PTH) was also measured by immunochemiluminescence (Immulite 2000, Diagnostic Products Corporation, Los Angeles, CA) in a subgroup of 38 patients. The normal range for serum PTH was 15–65 pg/ml, as established by the Central Laboratory of the Hospital.
Statistical analyses Results are expressed as means7SD unless otherwise stated. The Kolmogorov–Smirnov statistic was applied to continuous variables. Logarithmic or square root transformations were applied as needed to ensure a normal distribution of the variables. Serum levels of 25-hydroxyvitamin D were categorized in tertiles. Comparisons between the different groups were performed using unpaired t-test or Mann–Whitney U-test as appropriate for continuous variables, and using the w2-test or Fisher’s exact test for discontinuous variables, as needed. Pearson correlation was used to study the linear relationship between continuous variables. Multivariate logistic regression was performed in order to study the effects of multiple independent variables on having or not the metabolic syndrome. Analyses were performed using SPSS 10 for the Macintosh (SPSS Inc., Chicago, IL). Po0.05 was considered statistically significant.
Results Thirty-seven of the 73 morbidly obese patients (50.7%) had serum 25-hydroxyvitamin D levels below the 5th percentile of our reference population (20 ng/ml) and were considered vitamin D-deficient. Clinical and metabolic characteristics of patients with and without vitamin D deficiency are shown in Table 1. Age and gender were not different between groups. Although no difference in the mean serum PTH concentrations was found, 6 vitamin D-deficient patients (33.3%) had increased serum PTH concentration, compared
Table 1 Clinical and biochemical characteristics of morbidly obese patients included in the study, classified according to vitamin D status (n ¼ 73).
Gender, female/male (%) Age (years) Body mass index (kg/m2) Waist circumference (cm) Waist to hip ratio 25-Hydroxyvitamin D (ng/ml) Serum calcium (mg/dl) Parathyroid hormoney (pg/ml)
Patients without vitamin D deficiency (n ¼ 36)
Patients with vitamin D deficiency (n ¼ 37)
P-value
86.1/13.9 42.1711.6 49.879.8 123.8713.6 0.8970.11 45.7735.5 9.370.4 55.5712.6
78.4/21.6 39.0712.7 48.675.8 125.0714.4 0.8970.11 13.373.8 9.370.6 61.4725.7
0.388 0.283 0.516 0.711 0.885 o0.001 0.709 0.382
Data are means7SD. Vitamin D deficiency was defined as those values below 20 ng/dl (50 nmol/l) of serum 25-hydroxyvitamin D. y Measured in a subgroup of 38 patients, 18 with vitamin D deficiency (age 35712 years old, 84.2% women).
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Figure 1 Prevalence of vitamin D deficiency among morbid obese patients with and without the metabolic syndrome as defined by the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria.28 Black bars show patients with vitamin D deficiency as defined by serum 25-hydroxyvitamin D concentrations below 20 ng/ml. Gray bars show patients without vitamin D deficiency. *P ¼ 0.023.
with none of the subjects with normal serum 25-hydroxyvitamin D levels (w2 ¼ 7.917, P ¼ 0.007). The prevalence of the metabolic syndrome was 63% in the whole series of patients with morbid obesity. Vitamin D deficiency was more prevalent in morbidly obese patients presenting with the metabolic syndrome, compared with those who did not achieve the criteria for this syndrome (60.9% vs. 33.3% respectively, w2 ¼ 5.161, P ¼ 0.023) (Fig. 1). On the other hand, when patients were considered as having or not vitamin D insufficiency (25-hydroxyvitamin D levels between 20 and 32 ng/ml), the latter observation was not significant anymore (w2 ¼ 2.288, P ¼ 0.130). However, when serum concentrations of 25-hydroxyvitamin D were categorized in tertiles, there was an association of the prevalence of the metabolic syndrome with tertiles of 25hydroxyvitamin D (w2 ¼ 6.523, P ¼ 0.038) (Fig. 2). Gender did not influence the prevalence of the metabolic syndrome in vitamin D-deficient patients (60.0% in women and 76.9% in men, respectively, w2 ¼ 1.313, P ¼ 0.348). Dietary intake, as evaluated by the food frequency questionnaire, did not differ between morbidly obese patients with or without vitamin D deficiency in terms of total energy intake (10,65673580 and 997874112 kJ/day, respectively, P ¼ 0.573), total fat intake (106749 and 90735 g/day, respectively, P ¼ 0.239), protein intake (116734 and 109738 g/day, respectively, P ¼ 0.530), carbohydrate intake (2917128 and 2877158 g/day, respectively, P ¼ 0.931), calcium intake (1.170.4 and 1.170.5 g/ day, respectively, P ¼ 0.982) or dietary vitamin D intake (2547124 and 2727125 IU/day, respectively, P ¼ 0.649).
J.I. Botella-Carretero et al.
Figure 2 Prevalence of metabolic syndrome among tertiles of serum 25-hydroxyvitamin D concentrations. Black bars show patients with metabolic syndrome as defined by the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria.28 Gray bars show patients without metabolic syndrome. * P ¼ 0.038, yP ¼ 0.014.
We performed a multivariate logistic regression in which having or not the metabolic syndrome was introduced as the dependent variable, and vitamin D deficiency, calcium intake, age and gender were introduced as independent variables. In a backward stepwise likelihood ratio model, only vitamin D deficiency was a predictive variable for the metabolic syndrome (odds ratio: 3.111, 95% CI: 1.150–8.418, Nagelkerke’s R2 ¼ 0.095, w2 ¼ 5.236, P ¼ 0.022) in the morbidly obese patients studied here. When multivariate logistic regression was performed introducing tertiles of 25hydroxyvitamin D instead of vitamin D deficiency as an independent variable, only the former was retained by the model as a predictive variable for the metabolic syndrome (odds ratio: 0.472, 95% CI: 0.251–0.887, Nagelkerke’s R2 ¼ 0.105, w2 ¼ 5.858, P ¼ 0.016). As sunlight exposure can modify serum 25-hydroxyvitamin D concentrations, we also analyzed the possible impact of seasonal variations in sampling on our present results. Of the 73 patients, 36 were evaluated during the winter or spring, whereas 37 were evaluated during the summer or autumn, the latter representing the highest seasonal sunlight exposure effect on vitamin D3 synthesis at skin. We found no significant difference in the time of sampling between the group of morbidly obese patients with vitamin D deficiency (20 were evaluated at winter or springtime and 17 at summer or autumn), compared with those without vitamin D deficiency (16 at winter or springtime and 20 summer or autumn, w2 ¼ 0.674, P ¼ 0.412). In order to further study the influence of vitamin D deficiency on biochemical variables, patients who were
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Table 2 Clinical and biochemical characteristics of morbidly obese patients with and without vitamin D deficiency, who had not taken any drug known to influence lipid profile, blood pressure or insulin sensitivity (n ¼ 44).
Metabolic syndromey Gender female Age (years) Body mass index (kg/m2) Waist circumference (cm) Waist to hip ratio Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Total cholesterol (mg/dl) HDL-cholesterol (mg/dl) LDL-cholesterol (mg/dl) Triglycerides (mg/dl) Fasting glucose (mg/dl) Fasting insulin (mU/ml) HOMA-IR 25-Hydroxyvitamin D (ng/ml)
Patients without vitamin D deficiency (n ¼ 20)
Patients with vitamin D deficiency (n ¼ 24)
P-value
7 (35.0%) 19 (95.0%) 34.679.2 48.376.0 120.0710.8 0.8570.08 125.1710.0 74.178.2 178.4724.0 44.978.7 115.0717.1 95.1724.2 93.7718.8 18.1712.1 4.373.2 39.3719.3
17 (70.8%) 20 (83.3%) 34.179.7 48.476.5 123.1713.7 0.8770.11 128.7713.6 75.477.8 188.5740.2 37.077.8 117.3738.1 163.3781.5 97.0722.8 25.2716.4 6.374.9 13.373.7
0.017 0.356 0.845 0.985 0.418 0.481 0.361 0.589 0.307 0.003 0.804 0.001 0.618 0.143 0.154 o0.001
Data are means7SD for continuous variables and absolute count (%) for dichotomous variables.HDL, high density lipoprotein; LDL, low density lipoprotein; HOMA-IR, insulin resistance as determined by the homeostasis model assessment. Vitamin D deficiency was defined as those values below 20 ng/dl (50 nmol/l) of serum 25-hydroxyvitamin D. y The metabolic syndrome was defined by the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria.28
taking medications for hypertension, dyslipidemia and/or diabetes mellitus at the time of the study were excluded. Table 2 summarizes the clinical and biochemical characteristics of the 44 patients who were not receiving drug therapy, as categorized by their vitamin D status. As occurred in the whole series of patients, age and gender were similarly distributed in both groups, and the metabolic syndrome was more prevalent in vitamin D-deficient patients (Table 2). Serum HDL concentrations were lower, and triglycerides were higher in the vitamin D-deficient group (Table 2). Serum 25-hydroxyvitamin D concentrations showed a positive correlation with HDL concentrations (r ¼ 0.325, P ¼ 0.033) and a negative correlation with serum triglycerides (r ¼ 0.364, P ¼ 0.015). However, we found no significant differences on fasting glucose, insulin or insulin resistance between patients with or without vitamin D deficiency (Table 2).
Discussion We have shown that vitamin D deficiency is associated with the metabolic syndrome in morbidly obese patients, in relation with a decrease in serum HDL concentrations and an increase in serum triglycerides concentrations. Previous studies have shown this association between vitamin D deficiency and the metabolic syndrome in women23 and in the general population,22 and our present findings confirm these results also in morbidly obese people. However, previous studies showed an inverse relationship between vitamin D levels and BMI,23 as well as central adiposity,22 making difficult to distinguish the separate contributions of
obesity and of vitamin D to the development of the metabolic syndrome. Our results may be of special interest, given that our patients with and without vitamin D deficiency had similar BMI and waist circumference, so the differences in metabolic syndrome prevalence and lipid levels may indeed reflect a true association between vitamin D status and the metabolic syndrome, irrespective of adiposity. The high prevalence of vitamin D deficiency in obesity has been hypothesized to result by the sequestering effect of high quantity of subcutaneous fat on circulating vitamin D.27,37 But also, obese individuals, because of lower mobility or cosmetic problems, might have less exposure to solar ultraviolet radiation, which is responsible for more than 90% of the vitamin D requirement for most people.14,26 Both of these mechanisms may explain the high prevalence of vitamin D deficiency in severely obese individuals, which has been shown to be present up to a 60–80% of morbidly obese patients before bariatric surgical procedures,38–40 whereas vitamin D deficiency has been shown to affect approximately 40% of the general population.15 In our study, we have shown a prevalence of vitamin D deficiency of 50.7% among morbidly obese patients, also above the prevalence in the general population. Although a limitation of our study is that we did not quantify individual sunlight exposure, taking into account that vitamin D intake was similar in both patients with vitamin D deficiency and those without it, it is plausible that sunlight exposure might be responsible for individual differences in serum 25-hydroxyvitamin D levels in our patients. Besides, it is possible that climate variations may be responsible for the differences in the prevalence of vitamin D deficiency among different populations.
ARTICLE IN PRESS 578 In the last few years, there has been much controversy to what levels of PTH and 25-hydroxyvitamin D should be considered as normal,41 and there is a need to establish a normal range for both PTH and 25-hydroxyvitamin D in all age groups.41 In our study, we chose a cut-off value of 20 ng/ ml (50 nmol/l) based on the 5th percentile from those of a control group of 60 healthy blood donors to define vitamin D deficiency. This normal range is in accordance with the data reported from previous studies in sunny countries,31,32 and no patient with serum 25-hydroxyvitamin D concentrations above 20 ng/ml had secondary hyperparathyroidism in our study. However, some authors now advocate a cut-off value of 32 ng/ml (80 nmol/l) to define vitamin D sufficiency based on serum PTH concentrations regarded as normal,34,35 and to yield maximal calcium absorption from the intestine.33 Therefore, we also used this latter threshold to define vitamin D insufficiency. Although in this case, the association of the metabolic syndrome with vitamin D insufficiency was not statistically significant, we found that tertiles of serum 25-hydroxyvitamin D levels were associated with the prevalence of the metabolic syndrome, indicating that the lower vitamin D levels are, the more frequency of the metabolic syndrome is found in morbid obese patients. The most relevant finding in our study was the association of vitamin D concentrations with lipid levels. Our results are in concordance with the concept that vitamin D appears to be necessary to maintain adequate apolipoprotein A-I concentrations, the main component of HDL cholesterol. In a study conducted in a healthy Belgian population, those individuals with high vitamin D concentrations also had the highest plasma apolipoprotein A-I concentrations, and 25hydroxyvitamin D showed a positive correlation with serum HDL concentrations.42 Another study has shown that vitamin D deficiency is associated with reductions in serum apolipoprotein A-I, but failed to demonstrate a positive correlation between serum HDL concentrations and vitamin D.43 Furthermore, it has been recently shown that supplementation with calcium and vitamin D enhances the beneficial effect of weight loss on plasma lipoprotein concentrations.44 On the other hand, vitamin D supplementation in postmenopausal women has been shown to be associated with a decrease in HDL concentrations.45 However, in the latter study, there was also a similar decrease in HDL concentrations in the placebo group, and only postmenopausal women receiving estrogen replacement therapy showed unchanged HDL concentrations. Therefore, it seems that more research is necessary to unravel the precise effect of vitamin D on apolipoprotein A-I and HDL concentrations, although the current knowledge shows that this effect may depend on the specific studied population and concomitant diseases. A relationship between vitamin D and triglycerides concentrations has also been demonstrated, especially in studies with patients on hemodialysis, in whom treatment with calcitriol induced a decrease in serum triglycerides concentrations.46–48 However, it has been shown that ingestion of high dietary calcium also decreases triglycerides concentrations.49 However, in our study calcium intake was not different in patients with or without vitamin D deficiency, therefore excluding a major role for
J.I. Botella-Carretero et al. dietary calcium in altering triglycerides concentrations in our study. Vitamin D deficiency was linked to impaired insulin secretion in animal models many years ago,50 and these observations were confirmed later in humans.51 More recently, vitamin D deficiency has been associated with insulin resistance and beta cell dysfunction in healthy, glucose-tolerant subjects,52,53 and also in individuals at risk for the development of type 2 diabetes mellitus.53 We could not confirm this hypothesis in our study, possibly because the resultant small sample size after removing those patients on medications that could alter glucose and/or insulin concentrations, may have precluded us from reaching a significant effect of vitamin D deficiency on insulin resistance. Apart from vitamin D, it has been shown that high dietary intake of calcium and/or dairy products may reduce the risk for developing the metabolic syndrome, type 2 diabetes21 and cardiovascular disease.54 However, we did not find differences in dietary patterns, including calcium intake, in our morbidly obese patients with vitamin D deficiency when compared with those with vitamin D sufficiency. Besides, calcium intake as recorded by the food frequency questionnaire, was not associated with the metabolic syndrome in the multivariate logistic regression. Therefore, it seems improbable that calcium intake might have been a major contributing risk factor for the metabolic syndrome in our study. Our study has two limitations that have to be taken into account: first, as stated above, we measured 25-hydroxyvitamin D concentrations by ELISA, which is less reliable compared with other available methods (i.e. radioimmunoassay). Second, the food frequency questionnaire, although previously validated in the Spanish population,29 is neither specific for vitamin D or calcium intakes nor has been validated in obese people. In conclusion, vitamin D deficiency is associated with the metabolic syndrome in morbidly obese patients, in relation with a decrease in serum high-density lipoprotein cholesterol and an increase in serum triglycerides concentrations.
Acknowledgments This work was supported by Grants FIS PI050341 and 050551, and REDIMET RD06/0015/0007 from the Fondo de Investigacio ´n Sanitaria, Instituto de Salud Carlos III, Spanish Ministry of Health and Consumer Affairs. This Institution had no role in the study design, collection, analysis or interpretation of data, as well as in the decision to submission for publication. J.I.B.-C. was responsible for the conception and design of study, carried out most of the clinical studies recruiting and evaluating the patients, and performed collection, analysis and interpretation of data, statistical workout, drafting and final approval of the article. F.A.-B. contributed to recruit patients, collection, analysis and interpretation of data, drafting and final approval of the article. J.J.V. performed vitamin analysis, collection of data, and also contributed to drafting and final approval of the article. J.A.B. and C.V. contributed to recruit patients, collection of data, and also participated in drafting and final approval of the article. H.F.E.-M. contributed to the recruitment and evaluation of patients, was responsible for the conception, design and
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funding of the study, interpretation of data analysis, important contribution for intellectual content, drafting and final approval of the article.
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of cardiovascular disease among type 2 diabetic patients. Diabetes Care 2006;29:722–4. Pereira MA, Jacobs Jr DR, Van Horn L, Slattery ML, Kartashov AI, Ludwig DS. Dairy consumption, obesity, and the insulin resistance syndrome in young adults: the CARDIA Study. JAMA 2002;287:2081–9. Ford ES, Ajani UA, McGuire LC, Liu S. Concentrations of serum vitamin D and the metabolic syndrome among US adults. Diabetes Care 2005;28:1228–30. Liu S, Song Y, Ford ES, Manson JE, Buring JE, Ridker PM. Dietary calcium, vitamin D, and the prevalence of metabolic syndrome in middle-aged and older US women. Diabetes Care 2005;28: 2926–32. Nagpal S, Na S, Rathnachalam R. Noncalcemic actions of vitamin D receptor ligands. Endocr Rev 2005;26:662–87. Bell NH, Epstein S, Greene A, Shary J, Oexmann MJ, Shaw S. Evidence for alteration of the vitamin D-endocrine system in obese subjects. J Clin Invest 1985;76:370–3. Compston JE, Vedi S, Ledger JE, Webb A, Gazet JC, Pilkington TR. Vitamin D status and bone histomorphometry in gross obesity. Am J Clin Nutr 1981;34:2359–63. Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr 2000;72:690–3. Grundy SM, Cleeman JI, Daniels SR, Donato KA, Eckel RH, Franklin BA, et al. Diagnosis and management of the metabolic syndrome: an American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement. Circulation 2005;112:2735–52. Vioque J, Gonzalez L. Validity of a food frequency questionnaire (preliminary results). Eur J Cancer Prev 1991;1:S19–20. Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985;28:412–9. Aguado P, del Campo MT, Garces MV, Gonzalez-Casaus ML, Bernad M, Gijon-Banos J, et al. Low vitamin D levels in outpatient postmenopausal women from a rheumatology clinic in Madrid, Spain: their relationship with bone mineral density. Osteoporos Int 2000;11:739–44. Fuleihan GE, Deeb M. Hypovitaminosis D in a sunny country. N Engl J Med 1999;340:1840–1. Heaney RP, Dowell MS, Hale CA, Bendich A. Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D. J Am Coll Nutr 2003;22:142–6. Chapuy MC, Preziosi P, Maamer M, Arnaud S, Galan P, Hercberg S, et al. Prevalence of vitamin D insufficiency in an adult normal population. Osteoporos Int 1997;7:439–43. Gomez Alonso C, Naves Diaz M, Rodriguez Garcia M, Fernandez Martin JL, Cannata Andia JB. Review of the concept of vitamin D ‘‘sufficiency and insufficiency’’. Nefrologia 2003;23(Suppl. 2):73–7. Dawson-Hughes B, Heaney RP, Holick MF, Lips P, Meunier PJ, Vieth R. Estimates of optimal vitamin D status. Osteoporos Int 2005;16:713–6. Arunabh S, Pollack S, Yeh J, Aloia JF. Body fat content and 25hydroxyvitamin D levels in healthy women. J Clin Endocrinol Metab 2003;88:157–61. Manco M, Calvani M, Nanni G, Greco AV, Iaconelli A, Gasbarrini G, et al. Low 25-hydroxyvitamin d does not affect insulin sensitivity in obesity after bariatric surgery. Obes Res 2005;13:1692–700. Ybarra J, Sanchez-Hernandez J, Gich I, De Leiva A, Rius X, Rodriguez-Espinosa J, et al. Unchanged hypovitaminosis D and secondary hyperparathyroidism in morbid obesity after bariatric surgery. Obes Surg 2005;15:330–5. Buffington C, Walker B, Cowan Jr GS, Scruggs D. Vitamin D deficiency in the morbidly obese. Obes Surg 1993;3:421–4.
ARTICLE IN PRESS 580 41. Holick MF. The parathyroid hormone D-lema. J Clin Endocrinol Metab 2003;88:3499–500. 42. Auwerx J, Bouillon R, Kesteloot H. Relation between 25hydroxyvitamin D3, apolipoprotein A-I, and high density lipoprotein cholesterol. Arterioscler Thromb 1992;12:671–4. 43. John WG, Noonan K, Mannan N, Boucher BJ. Hypovitaminosis D is associated with reductions in serum apolipoprotein A-I but not with fasting lipids in British Bangladeshis. Am J Clin Nutr 2005;82:517–22. 44. Major GC, Alarie F, Dore J, Phouttama S, Tremblay A. Supplementation with calcium+vitamin D enhances the beneficial effect of weight loss on plasma lipid and lipoprotein concentrations. Am J Clin Nutr 2007;85:54–9. 45. Heikkinen AM, Tuppurainen MT, Niskanen L, Komulainen M, Penttila I, Saarikoski S. Long-term vitamin D3 supplementation may have adverse effects on serum lipids during postmenopausal hormone replacement therapy. Eur J Endocrinol 1997;137: 495–502. 46. Khajehdehi P, Taheri S. Effect of oral calcitriol pulse therapy on the lipid, calcium, and glucose homeostasis of hemodialysispatients: its safety in a combination with oral calcium carbonate. J Ren Nutr 2003;13:78–83. 47. Khajehdehi P. Effect of vitamins on the lipid profile of patients on regular hemodialysis. Scand J Urol Nephrol 2000;34:62–6.
J.I. Botella-Carretero et al. 48. Lin SH, Lin YF, Lu KC, et al. Effects of intravenous calcitriol on lipid profiles and glucose tolerance in uraemic patients with secondary hyperparathyroidism. Clin Sci (London) 1994;87: 533–8. 49. Papakonstantinou E, Flatt WP, Huth PJ, Harris RB. High dietary calcium reduces body fat content, digestibility of fat, and serum vitamin D in rats. Obes Res 2003;11:387–94. 50. Norman AW, Frankel JB, Heldt AM, Grodsky GM. Vitamin D deficiency inhibits pancreatic secretion of insulin. Science 1980;209:823–5. 51. Gedik O, Akalin S. Effects of vitamin D deficiency and repletion on insulin and glucagon secretion in man. Diabetologia 1986;29:142–5. 52. Chiu KC, Chu A, Go VL, Saad MF. Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction. Am J Clin Nutr 2004;79:820–5. 53. Boucher BJ, Mannan N, Noonan K, Hales CN, Evans SJ. Glucose intolerance and impairment of insulin secretion in relation to vitamin D deficiency in east London Asians. Diabetologia 1995;38:1239–45. 54. Bostick RM, Kushi LH, Wu Y, Meyer KA, Sellers TA, Folsom AR. Relation of calcium, vitamin D, and dairy food intake to ischemic heart disease mortality among postmenopausal women. Am J Epidemiol 1999;149:151–61.
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ORIGINAL ARTICLE
Vitamin D deficiency is associated with the metabolic syndrome in morbid obesity$ Jose ´ I. Botella-Carreteroa,b,, Francisco Alvarez-Blascob, Juan J. Villafruelac, ´zqueza, He ´ctor F. Escobar-Morrealeb Jose ´ A. Balsaa, Clotilde Va a
Department of Clinical Nutrition, Hospital Ramo ´n y Cajal, 28034 Madrid, Spain Department of Endocrinology, Hospital Ramo ´n y Cajal, 28034 Madrid, Spain c Department of Nephrology, Hospital Ramo ´n y Cajal, 28034 Madrid, Spain b
Received 14 December 2006; accepted 24 May 2007
KEYWORDS Vitamin D; Metabolic syndrome; Obesity; Lipids; Insulin resistance
Summary Background & aims: Vitamin D deficiency has been recently associated with the metabolic syndrome. However, it is not known whether this possible association of vitamin D deficiency with the metabolic syndrome is still present at very high degrees of obesity, as in morbidly obese patients. Methods: Transversal, observational study that included 73 consecutive morbidly obese patients (body mass index X40 kg/m2). In every patient, anthropometric variables were recorded, fasting blood was assayed for 25-hydroxyvitamin D concentrations, lipid profiles, glucose and insulin levels, and insulin resistance was estimated by homeostasis model assessment. Results: Vitamin D deficiency was present in 37 of the 73 patients (50.7%). As defined by revised Adult Treatment Panel III criteria, 46 of the 73 obese patients (63%) had the metabolic syndrome. Vitamin D deficiency was more prevalent in morbidly obese patients presenting with the metabolic syndrome, compared with those who did not achieve the criteria for this syndrome (60.9% vs. 33.3% respectively, P ¼ 0.023). When serum concentrations of 25-hydroxyvitamin D were categorized in tertiles, there was an association of the prevalence of the metabolic syndrome with the former (P ¼ 0.038). Serum high-density lipoprotein cholesterol concentrations were lower (37.077.8 mg/dl vs. 44.978.7 mg/dl, P ¼ 0.003), and triglycerides levels were higher (163.3781.5 mg/dl vs. 95.1724.2 mg/dl, P ¼ 0.001) in the vitamin D-deficient group.
Abbreviations: BMI, body mass index; HDL, high density lipoprotein; LDL, low density lipoprotein; HOMA-IR, insulin resistance as determined by the homeostasis model assessment $ Conference presentation: Presented in part at the Press Conference of the Endocrine Society’s 88th Annual Meeting, Boston, 2006. Corresponding author. Department of Clinical Nutrition, Hospital Ramo ´n y Cajal, Carretera de Colmenar Km. 9.1, 28034 Madrid, Spain. Tel.: +34 91 336 8726; fax: +34 91 336 9029. E-mail address: [email protected] (J.I. Botella-Carretero). 0261-5614/$ - see front matter & 2007 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved. doi:10.1016/j.clnu.2007.05.009
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J.I. Botella-Carretero et al. Conclusion: Vitamin D deficiency is associated with the metabolic syndrome in morbidly obese patients. & 2007 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.
Introduction Obesity is a major public health problem in Western countries. The prevalence of obesity has significantly increased among these countries population over the past 30 years, and recent data estimate that nearly one-third of adults are obese.1,2 The impact of obesity on public health is profound, as it has been shown to be a major risk factor for cardiovascular disease3,4 and cancer,5 with a consequent reduction in life expectancy.6,7 Obesity is a major contributor to the constellation of cardiovascular disease risk factors associated with insulin resistance (glucose intolerance, dyslipidemia, hypertension, and central adiposity), commonly referred to as the metabolic syndrome.8 The metabolic syndrome has been estimated to affect more than 20% of adults in the United States,9 and it has been shown that its prevalence increases with worsening obesity.10,11 Vitamin D is known for the maintenance of mineral homeostasis and normal skeletal architecture. The precursor provitamin D, 7-dehydrocholesterol, absorbs ultraviolet radiation in the skin and is transformed into previtamin D3, which is rapidly converted to vitamin D3. The latter is metabolized in the liver to 25-hydroxyvitamin D3 and then in the kidney to its biologically active form 1,25-dihydroxyvitamin D3.12 Vitamin D also comes from diet in the form of vitamin D2 (ergocalciferol), mostly from fortified foods but also in small quantities from plant sources and irritated yeast, and in the form of vitamin D3 (cholecalciferol) from animal sources. Both vitamin D2 and vitamin D3 can be hydroxylated in the liver and later in the kidney, resulting in the biologically active form of vitamin D. Vitamin D deficiency, as determined by decreased serum concentrations of 25-hydroxyvitamin D,13,14 has become epidemic for all age groups in the United States and Europe.15,16 This occurs even in spite of fortification of certain foods, such as cereals and dairy products among others, with vitamin D.13 Besides, it has been shown that serum concentrations of 25-hydroxyvitamin D in people living in sun-rich environments where clothing or cultural practices do not prevent sun exposure, are much higher than in those with little sun exposure.17 Therefore, a reduction in sun exposure due to sunscreens, climate variations, clothing or cultural practices, together with inadequate ingestion of vitamin D through an ordinary diet, may produce vitamin D deficiency.14,17 Vitamin D deficiency not only causes metabolic bone disease, but may also increase the risk of other common chronic disorders.14 During the past few years, vitamin D deficiency has been linked to type 2 diabetes mellitus18,19 and cardiovascular risk.14,20 Furthermore, a possible role of vitamin D deficiency in the pathogenesis of the metabolic syndrome has been also recently suggested.21–23
Non-calcemic actions of vitamin D have been proposed to be responsible for these associations, because most cells and tissues in the body harbor the vitamin D receptor.24 Yet also, vitamin D deficiency is more prevalent in obese persons,25,26 and it has been proposed that this may result from accumulation of vitamin D in adipose tissue.27 As there is an inverse relationship between vitamin D levels and the degree of obesity,23 as well as with central adiposity,22 it has been difficult to distinguish the independent effects of obesity and vitamin D on metabolic syndrome. Furthermore, it is not known whether the association of vitamin D deficiency with the metabolic syndrome is still present at very high degrees of obesity, in which the possible effect of vitamin D status on the metabolic syndrome could be ameliorated or even completely overcome by the predominant effect of obesity. Therefore, we conducted this study to investigate the possible association of vitamin D status with the metabolic syndrome, its individual components, and insulin resistance in a cohort of morbidly obese patients. As it will be seen, given that the patients in our study with and without vitamin D deficiency had similar degree of obesity and waist circumference, the differences in metabolic syndrome prevalence and lipid levels found here may indeed reflect a true association between vitamin D status and the latter, irrespective of adiposity.
Patients and methods Subjects and study protocol Seventy-three consecutive morbidly obese patients (defined by a BMIX40 kg/m2) reporting to the Department of Clinical Nutrition of Hospital Ramo ´n y Cajal for bariatric surgery were recruited. All the subjects were Caucasian from European ancestry. Twenty-seven were on anti-hypertensive medication, seven were on blood glucose lowering drugs and/or insulin, and seven were on statins and/or fibrates. None of them were taking supplements of calcium and/or vitamin D, or any drug known to influence their concentrations aside from the aforementioned medication. None of the patients had intestinal malabsorption, nor inflammatory bowel disease. The ethics committee of the Hospital Ramo ´n y Cajal approved the protocol, and informed consent was obtained from each patient. Between 8 and 9 a.m. and after a 12-h overnight fast, an indwelling intravenous line was placed in a forearm vein and, after 15–30 min, basal blood samples were obtained in each patient. Body mass index, office blood pressure and waist to hip ratio were also recorded. All patients were evaluated before bariatric surgery. The diagnosis of the metabolic syndrome required the presence of three or more
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of the following criteria: abdominal obesity (waist circumference 4102 cm in men and 488 cm in women), triglycerides X150 mg/dl, high-density lipoprotein cholesterol (HDL) o40 mg/dl in men and o50 mg/dl in women, blood pressure X130/80 mmHg, fasting glucose X100 mg/dl, according to the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III28. Patients receiving pharmacological treatment for diabetes, hypertension or hypertriglyceridemia were considered as matching the corresponding criteria. In order to evaluate dietary patterns, we employed a food frequency questionnaire that has been previously validated in the Spanish population.29
Analytical procedures and reference ranges Lipid profiles including total cholesterol, low-density lipoprotein cholesterol (LDL), HDL, triglycerides and fasting glucose were analyzed using an Abbott Aeroset Automated Instrument Analyzer (Abbott Laboratories, Abbot Park, IL) with mean intra- and interassay coefficients of variation (CVs) below 2%. Fasting insulin was measured by immunochemiluminescence (Immulite 2000, Diagnostic Products Corporation, Los Angeles, CA) with mean CVs below 10%. Insulin resistance in the fasting state (HOMA-IR) was estimated from glucose and insulin concentrations using homeostasis model assessment.30 A commercial enzyme linked immunosorbent assay (ELISA) was employed for the measurement of 25-hydroxyvitamin D concentrations (IDS Ltd., Boldon, UK). The specificity of this assay is 100% for 25-hydroxyvitamin D3 and 75% for 25-hydroxyvitamin D2, and negligible cross-reactivity with vitamin D3 and vitamin D2 (o0.01% and o0.30%, respectively). The normal range for 25-hydroxyvitamin D plasma concentration was defined at our Institution by the 5th and 95th percentiles of a control group of 60 healthy blood donors, which were 20 and 60 ng/ml (50 and 150 nmol/l), respectively. This normal range is in accordance to the data reported from previous studies in sunny countries.31,32 However, as recent studies have proposed that levels equal to or above 32 ng/ml (80 nmol/l)17 are necessary for
maximal calcium absorption from the intestine,33 and to universally avoid secondary hyperparathyroidism,34,35 we defined vitamin D insufficiency as those levels between 20 and 32 ng/ml (50 and 80 nmol/l, respectively), and vitamin D deficiency as those below 20 ng/ml (50 nmol/l).36 Parathyroid hormone (PTH) was also measured by immunochemiluminescence (Immulite 2000, Diagnostic Products Corporation, Los Angeles, CA) in a subgroup of 38 patients. The normal range for serum PTH was 15–65 pg/ml, as established by the Central Laboratory of the Hospital.
Statistical analyses Results are expressed as means7SD unless otherwise stated. The Kolmogorov–Smirnov statistic was applied to continuous variables. Logarithmic or square root transformations were applied as needed to ensure a normal distribution of the variables. Serum levels of 25-hydroxyvitamin D were categorized in tertiles. Comparisons between the different groups were performed using unpaired t-test or Mann–Whitney U-test as appropriate for continuous variables, and using the w2-test or Fisher’s exact test for discontinuous variables, as needed. Pearson correlation was used to study the linear relationship between continuous variables. Multivariate logistic regression was performed in order to study the effects of multiple independent variables on having or not the metabolic syndrome. Analyses were performed using SPSS 10 for the Macintosh (SPSS Inc., Chicago, IL). Po0.05 was considered statistically significant.
Results Thirty-seven of the 73 morbidly obese patients (50.7%) had serum 25-hydroxyvitamin D levels below the 5th percentile of our reference population (20 ng/ml) and were considered vitamin D-deficient. Clinical and metabolic characteristics of patients with and without vitamin D deficiency are shown in Table 1. Age and gender were not different between groups. Although no difference in the mean serum PTH concentrations was found, 6 vitamin D-deficient patients (33.3%) had increased serum PTH concentration, compared
Table 1 Clinical and biochemical characteristics of morbidly obese patients included in the study, classified according to vitamin D status (n ¼ 73).
Gender, female/male (%) Age (years) Body mass index (kg/m2) Waist circumference (cm) Waist to hip ratio 25-Hydroxyvitamin D (ng/ml) Serum calcium (mg/dl) Parathyroid hormoney (pg/ml)
Patients without vitamin D deficiency (n ¼ 36)
Patients with vitamin D deficiency (n ¼ 37)
P-value
86.1/13.9 42.1711.6 49.879.8 123.8713.6 0.8970.11 45.7735.5 9.370.4 55.5712.6
78.4/21.6 39.0712.7 48.675.8 125.0714.4 0.8970.11 13.373.8 9.370.6 61.4725.7
0.388 0.283 0.516 0.711 0.885 o0.001 0.709 0.382
Data are means7SD. Vitamin D deficiency was defined as those values below 20 ng/dl (50 nmol/l) of serum 25-hydroxyvitamin D. y Measured in a subgroup of 38 patients, 18 with vitamin D deficiency (age 35712 years old, 84.2% women).
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Figure 1 Prevalence of vitamin D deficiency among morbid obese patients with and without the metabolic syndrome as defined by the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria.28 Black bars show patients with vitamin D deficiency as defined by serum 25-hydroxyvitamin D concentrations below 20 ng/ml. Gray bars show patients without vitamin D deficiency. *P ¼ 0.023.
with none of the subjects with normal serum 25-hydroxyvitamin D levels (w2 ¼ 7.917, P ¼ 0.007). The prevalence of the metabolic syndrome was 63% in the whole series of patients with morbid obesity. Vitamin D deficiency was more prevalent in morbidly obese patients presenting with the metabolic syndrome, compared with those who did not achieve the criteria for this syndrome (60.9% vs. 33.3% respectively, w2 ¼ 5.161, P ¼ 0.023) (Fig. 1). On the other hand, when patients were considered as having or not vitamin D insufficiency (25-hydroxyvitamin D levels between 20 and 32 ng/ml), the latter observation was not significant anymore (w2 ¼ 2.288, P ¼ 0.130). However, when serum concentrations of 25-hydroxyvitamin D were categorized in tertiles, there was an association of the prevalence of the metabolic syndrome with tertiles of 25hydroxyvitamin D (w2 ¼ 6.523, P ¼ 0.038) (Fig. 2). Gender did not influence the prevalence of the metabolic syndrome in vitamin D-deficient patients (60.0% in women and 76.9% in men, respectively, w2 ¼ 1.313, P ¼ 0.348). Dietary intake, as evaluated by the food frequency questionnaire, did not differ between morbidly obese patients with or without vitamin D deficiency in terms of total energy intake (10,65673580 and 997874112 kJ/day, respectively, P ¼ 0.573), total fat intake (106749 and 90735 g/day, respectively, P ¼ 0.239), protein intake (116734 and 109738 g/day, respectively, P ¼ 0.530), carbohydrate intake (2917128 and 2877158 g/day, respectively, P ¼ 0.931), calcium intake (1.170.4 and 1.170.5 g/ day, respectively, P ¼ 0.982) or dietary vitamin D intake (2547124 and 2727125 IU/day, respectively, P ¼ 0.649).
J.I. Botella-Carretero et al.
Figure 2 Prevalence of metabolic syndrome among tertiles of serum 25-hydroxyvitamin D concentrations. Black bars show patients with metabolic syndrome as defined by the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria.28 Gray bars show patients without metabolic syndrome. * P ¼ 0.038, yP ¼ 0.014.
We performed a multivariate logistic regression in which having or not the metabolic syndrome was introduced as the dependent variable, and vitamin D deficiency, calcium intake, age and gender were introduced as independent variables. In a backward stepwise likelihood ratio model, only vitamin D deficiency was a predictive variable for the metabolic syndrome (odds ratio: 3.111, 95% CI: 1.150–8.418, Nagelkerke’s R2 ¼ 0.095, w2 ¼ 5.236, P ¼ 0.022) in the morbidly obese patients studied here. When multivariate logistic regression was performed introducing tertiles of 25hydroxyvitamin D instead of vitamin D deficiency as an independent variable, only the former was retained by the model as a predictive variable for the metabolic syndrome (odds ratio: 0.472, 95% CI: 0.251–0.887, Nagelkerke’s R2 ¼ 0.105, w2 ¼ 5.858, P ¼ 0.016). As sunlight exposure can modify serum 25-hydroxyvitamin D concentrations, we also analyzed the possible impact of seasonal variations in sampling on our present results. Of the 73 patients, 36 were evaluated during the winter or spring, whereas 37 were evaluated during the summer or autumn, the latter representing the highest seasonal sunlight exposure effect on vitamin D3 synthesis at skin. We found no significant difference in the time of sampling between the group of morbidly obese patients with vitamin D deficiency (20 were evaluated at winter or springtime and 17 at summer or autumn), compared with those without vitamin D deficiency (16 at winter or springtime and 20 summer or autumn, w2 ¼ 0.674, P ¼ 0.412). In order to further study the influence of vitamin D deficiency on biochemical variables, patients who were
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Table 2 Clinical and biochemical characteristics of morbidly obese patients with and without vitamin D deficiency, who had not taken any drug known to influence lipid profile, blood pressure or insulin sensitivity (n ¼ 44).
Metabolic syndromey Gender female Age (years) Body mass index (kg/m2) Waist circumference (cm) Waist to hip ratio Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Total cholesterol (mg/dl) HDL-cholesterol (mg/dl) LDL-cholesterol (mg/dl) Triglycerides (mg/dl) Fasting glucose (mg/dl) Fasting insulin (mU/ml) HOMA-IR 25-Hydroxyvitamin D (ng/ml)
Patients without vitamin D deficiency (n ¼ 20)
Patients with vitamin D deficiency (n ¼ 24)
P-value
7 (35.0%) 19 (95.0%) 34.679.2 48.376.0 120.0710.8 0.8570.08 125.1710.0 74.178.2 178.4724.0 44.978.7 115.0717.1 95.1724.2 93.7718.8 18.1712.1 4.373.2 39.3719.3
17 (70.8%) 20 (83.3%) 34.179.7 48.476.5 123.1713.7 0.8770.11 128.7713.6 75.477.8 188.5740.2 37.077.8 117.3738.1 163.3781.5 97.0722.8 25.2716.4 6.374.9 13.373.7
0.017 0.356 0.845 0.985 0.418 0.481 0.361 0.589 0.307 0.003 0.804 0.001 0.618 0.143 0.154 o0.001
Data are means7SD for continuous variables and absolute count (%) for dichotomous variables.HDL, high density lipoprotein; LDL, low density lipoprotein; HOMA-IR, insulin resistance as determined by the homeostasis model assessment. Vitamin D deficiency was defined as those values below 20 ng/dl (50 nmol/l) of serum 25-hydroxyvitamin D. y The metabolic syndrome was defined by the recently revisited Third Report of the National Cholesterol Education Program, Adult Treatment Panel III (NCEP-ATP III) criteria.28
taking medications for hypertension, dyslipidemia and/or diabetes mellitus at the time of the study were excluded. Table 2 summarizes the clinical and biochemical characteristics of the 44 patients who were not receiving drug therapy, as categorized by their vitamin D status. As occurred in the whole series of patients, age and gender were similarly distributed in both groups, and the metabolic syndrome was more prevalent in vitamin D-deficient patients (Table 2). Serum HDL concentrations were lower, and triglycerides were higher in the vitamin D-deficient group (Table 2). Serum 25-hydroxyvitamin D concentrations showed a positive correlation with HDL concentrations (r ¼ 0.325, P ¼ 0.033) and a negative correlation with serum triglycerides (r ¼ 0.364, P ¼ 0.015). However, we found no significant differences on fasting glucose, insulin or insulin resistance between patients with or without vitamin D deficiency (Table 2).
Discussion We have shown that vitamin D deficiency is associated with the metabolic syndrome in morbidly obese patients, in relation with a decrease in serum HDL concentrations and an increase in serum triglycerides concentrations. Previous studies have shown this association between vitamin D deficiency and the metabolic syndrome in women23 and in the general population,22 and our present findings confirm these results also in morbidly obese people. However, previous studies showed an inverse relationship between vitamin D levels and BMI,23 as well as central adiposity,22 making difficult to distinguish the separate contributions of
obesity and of vitamin D to the development of the metabolic syndrome. Our results may be of special interest, given that our patients with and without vitamin D deficiency had similar BMI and waist circumference, so the differences in metabolic syndrome prevalence and lipid levels may indeed reflect a true association between vitamin D status and the metabolic syndrome, irrespective of adiposity. The high prevalence of vitamin D deficiency in obesity has been hypothesized to result by the sequestering effect of high quantity of subcutaneous fat on circulating vitamin D.27,37 But also, obese individuals, because of lower mobility or cosmetic problems, might have less exposure to solar ultraviolet radiation, which is responsible for more than 90% of the vitamin D requirement for most people.14,26 Both of these mechanisms may explain the high prevalence of vitamin D deficiency in severely obese individuals, which has been shown to be present up to a 60–80% of morbidly obese patients before bariatric surgical procedures,38–40 whereas vitamin D deficiency has been shown to affect approximately 40% of the general population.15 In our study, we have shown a prevalence of vitamin D deficiency of 50.7% among morbidly obese patients, also above the prevalence in the general population. Although a limitation of our study is that we did not quantify individual sunlight exposure, taking into account that vitamin D intake was similar in both patients with vitamin D deficiency and those without it, it is plausible that sunlight exposure might be responsible for individual differences in serum 25-hydroxyvitamin D levels in our patients. Besides, it is possible that climate variations may be responsible for the differences in the prevalence of vitamin D deficiency among different populations.
ARTICLE IN PRESS 578 In the last few years, there has been much controversy to what levels of PTH and 25-hydroxyvitamin D should be considered as normal,41 and there is a need to establish a normal range for both PTH and 25-hydroxyvitamin D in all age groups.41 In our study, we chose a cut-off value of 20 ng/ ml (50 nmol/l) based on the 5th percentile from those of a control group of 60 healthy blood donors to define vitamin D deficiency. This normal range is in accordance with the data reported from previous studies in sunny countries,31,32 and no patient with serum 25-hydroxyvitamin D concentrations above 20 ng/ml had secondary hyperparathyroidism in our study. However, some authors now advocate a cut-off value of 32 ng/ml (80 nmol/l) to define vitamin D sufficiency based on serum PTH concentrations regarded as normal,34,35 and to yield maximal calcium absorption from the intestine.33 Therefore, we also used this latter threshold to define vitamin D insufficiency. Although in this case, the association of the metabolic syndrome with vitamin D insufficiency was not statistically significant, we found that tertiles of serum 25-hydroxyvitamin D levels were associated with the prevalence of the metabolic syndrome, indicating that the lower vitamin D levels are, the more frequency of the metabolic syndrome is found in morbid obese patients. The most relevant finding in our study was the association of vitamin D concentrations with lipid levels. Our results are in concordance with the concept that vitamin D appears to be necessary to maintain adequate apolipoprotein A-I concentrations, the main component of HDL cholesterol. In a study conducted in a healthy Belgian population, those individuals with high vitamin D concentrations also had the highest plasma apolipoprotein A-I concentrations, and 25hydroxyvitamin D showed a positive correlation with serum HDL concentrations.42 Another study has shown that vitamin D deficiency is associated with reductions in serum apolipoprotein A-I, but failed to demonstrate a positive correlation between serum HDL concentrations and vitamin D.43 Furthermore, it has been recently shown that supplementation with calcium and vitamin D enhances the beneficial effect of weight loss on plasma lipoprotein concentrations.44 On the other hand, vitamin D supplementation in postmenopausal women has been shown to be associated with a decrease in HDL concentrations.45 However, in the latter study, there was also a similar decrease in HDL concentrations in the placebo group, and only postmenopausal women receiving estrogen replacement therapy showed unchanged HDL concentrations. Therefore, it seems that more research is necessary to unravel the precise effect of vitamin D on apolipoprotein A-I and HDL concentrations, although the current knowledge shows that this effect may depend on the specific studied population and concomitant diseases. A relationship between vitamin D and triglycerides concentrations has also been demonstrated, especially in studies with patients on hemodialysis, in whom treatment with calcitriol induced a decrease in serum triglycerides concentrations.46–48 However, it has been shown that ingestion of high dietary calcium also decreases triglycerides concentrations.49 However, in our study calcium intake was not different in patients with or without vitamin D deficiency, therefore excluding a major role for
J.I. Botella-Carretero et al. dietary calcium in altering triglycerides concentrations in our study. Vitamin D deficiency was linked to impaired insulin secretion in animal models many years ago,50 and these observations were confirmed later in humans.51 More recently, vitamin D deficiency has been associated with insulin resistance and beta cell dysfunction in healthy, glucose-tolerant subjects,52,53 and also in individuals at risk for the development of type 2 diabetes mellitus.53 We could not confirm this hypothesis in our study, possibly because the resultant small sample size after removing those patients on medications that could alter glucose and/or insulin concentrations, may have precluded us from reaching a significant effect of vitamin D deficiency on insulin resistance. Apart from vitamin D, it has been shown that high dietary intake of calcium and/or dairy products may reduce the risk for developing the metabolic syndrome, type 2 diabetes21 and cardiovascular disease.54 However, we did not find differences in dietary patterns, including calcium intake, in our morbidly obese patients with vitamin D deficiency when compared with those with vitamin D sufficiency. Besides, calcium intake as recorded by the food frequency questionnaire, was not associated with the metabolic syndrome in the multivariate logistic regression. Therefore, it seems improbable that calcium intake might have been a major contributing risk factor for the metabolic syndrome in our study. Our study has two limitations that have to be taken into account: first, as stated above, we measured 25-hydroxyvitamin D concentrations by ELISA, which is less reliable compared with other available methods (i.e. radioimmunoassay). Second, the food frequency questionnaire, although previously validated in the Spanish population,29 is neither specific for vitamin D or calcium intakes nor has been validated in obese people. In conclusion, vitamin D deficiency is associated with the metabolic syndrome in morbidly obese patients, in relation with a decrease in serum high-density lipoprotein cholesterol and an increase in serum triglycerides concentrations.
Acknowledgments This work was supported by Grants FIS PI050341 and 050551, and REDIMET RD06/0015/0007 from the Fondo de Investigacio ´n Sanitaria, Instituto de Salud Carlos III, Spanish Ministry of Health and Consumer Affairs. This Institution had no role in the study design, collection, analysis or interpretation of data, as well as in the decision to submission for publication. J.I.B.-C. was responsible for the conception and design of study, carried out most of the clinical studies recruiting and evaluating the patients, and performed collection, analysis and interpretation of data, statistical workout, drafting and final approval of the article. F.A.-B. contributed to recruit patients, collection, analysis and interpretation of data, drafting and final approval of the article. J.J.V. performed vitamin analysis, collection of data, and also contributed to drafting and final approval of the article. J.A.B. and C.V. contributed to recruit patients, collection of data, and also participated in drafting and final approval of the article. H.F.E.-M. contributed to the recruitment and evaluation of patients, was responsible for the conception, design and
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funding of the study, interpretation of data analysis, important contribution for intellectual content, drafting and final approval of the article.
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