- Email: [email protected]
Serum 25-Hydroxyvitamin D Levels in Relation to Lung Function and Exhaled Nitric Oxide in Children
Serum 25-Hydroxyvitamin D Levels in Relation to Lung Function and Exhaled Nitric Oxide in Children Tsung-Chieh Yao, MD, PhD1,2, Yu-Ling Tu, MD1,2,3, Su-Wei Chang, PhD4, Hui-Ju Tsai, PhD5,6,7, Po-Wen Gu, MS8, Hsian-Chen Ning, MS8, Man-Chin Hua, MD2,9, Sui-Ling Liao, MD2,9, Ming-Han Tsai, MD, PhD2,9, Chih-Yung Chiu, MD, PhD2,9, Shen-Hao Lai, MD2,10, Kuo-Wei Yeh, MD1,2, and Jing-Long Huang, MD1,2, on behalf of the Prediction of Allergies in Taiwanese Children (PATCH) Study Group* Objective To investigate the relationship of vitamin D status with lung function and fraction of exhaled nitric oxide (FeNO) in a population sample of children.
Study design A total of 1315 children aged 5-18 years were evaluated using serum 25-hydroxyvitamin D [25(OH) D] levels, spirometry, a single-breath online FeNO measurement, and questionnaires.
Results After adjusting for confounders, the mean forced vital capacity was 53.4 mL (SE, 26.5 mL; P = .045), and the mean forced expiratory volume in 1 second was 48.2 mL (SE, 23.6 mL; P = .042) lower for children with insufficient serum 25(OH)D levels (20-29.9 ng/mL) compared with those with sufficient 25(OH)D levels ($30 ng/mL). The mean difference between children with deficient (<20 ng/mL) and sufficient levels of serum 25(OH)D was 81.9 mL (SE, 26.7 mL; P = .002) for forced vital capacity and 55.2 mL (SE, 23.7 mL; P = .020) for forced expiratory volume in 1 second. There was no significant association between serum 25(OH)D levels and FeNO after adjusting for confounders. Conclusions Our results demonstrate a significant relationship between insufficient serum vitamin D levels and worse lung function in children in the community with a suggested dose-response effect. Our findings also suggest that vitamin D status is not a significant determinant of FeNO in children in the general population. (J Pediatr 2014;-:---).
L
ung function, as assessed by the spirometric measures of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), the FEV1 to FVC ratio (FEV1/FVC), peak expiratory flow (PEF), and forced expiratory flow at 25%-75% (FEF25-75), is an objective indicator of general respiratory health. Lung development peaks between the ages of 20 and 25 years, is stable for 5-10 years, and then declines with increasing age.1 Mild perturbations in lung function, which may not be clinically apparent, have been shown to be an important long-term predictor of all-cause mortality and morbidity.2-6 Although variation in lung function between individuals is in part genetically determined,7 a significant proportion of the variation in lung function remains unexplained. The fraction of exhaled nitric oxide (FeNO) is a noninvasive biomarker of From the Division of Allergy, Asthma, and airway inflammation. We have demonstrated that FeNO discriminates children Rheumatology, Department of Pediatrics, Chang Gung with and without allergic sensitization independent of allergic symptoms in a Memorial Hospital and Chang Gung University College of Medicine, Taoyuan, Taiwan; Community Medicine population-based study.8 Although previous studies by our group8,9 and Research Center, Chang Gung Memorial Hospital at 10-15 Keelung, Keelung, Taiwan; Graduate Institute of Clinical others have identified important determinants of FeNO, the variation in Medical Sciences and Clinical Informatics and Medical FeNO levels at the population level remains partially unknown. Statistics Research Center, Chang Gung University College of Medicine, Taoyuan, Taiwan; Division of In addition to its historically well-known effects on calcium homeostasis and Biostatistics and Bioinformatics, Institutes of Population Health Sciences, National Health Research Institutes, bone metabolism, vitamin D is now recognized to play a role in the immune sysMiaoli, Taiwan; Department of Pediatrics, Feinberg 16 School of Medicine, Northwestern University, Chicago, tem, cardiovascular system, and cancer prevention. Recently, a few studies have IL; Department of Genome Medicine, Kaohsiung investigated the relationship of vitamin D to lung function in individuals with lung University, Kaohsiung, Taiwan; Department of Laboratory Medicine, Chang Gung Memorial Hospital, diseases, although the results have been conflicting. Some studies have found posTaoyuan, Taiwan; Department of Pediatrics, Chang Gung Memorial Hospital at Keelung, Keelung, Taiwan; itive associations between serum 25-hydroxyvitamin D [25(OH)D] levels and lung 1
2
3
4
5
6
7
8
9
and 10Division of Pediatric Pulmonology, Department of Pediatrics, Chang Gung Memorial Hospital, Taoyuan, Taiwan
25(OH)D BMI FEF25-75 FeNO FEV1 FVC NO PEF
25-hydroxyvitamin D Body mass index Forced expiratory flow at 25%-75% Fraction of exhaled nitric oxide Forced expiratory volume in 1 second Forced vital capacity Nitric oxide Peak expiratory flow
*List of members of the PATCH Study Group is available at www.jpeds.com (Appendix). Supported by the National Science Council Taiwan (101-2314-B-182A-044, 102-2314-B-182A-048, and 101-2314-B-400-009-MY2) and Chang Gung Memorial Hospital (CMRPG260291260293, CMRPG2B00712B0073, and CMRPG4B00314B0033). The authors declare no conflicts of interest. 0022-3476/$ - see front matter. Copyright ª 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jpeds.2014.08.048
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function in adults17,18 and children19,20 with asthma and in patients with chronic obstructive pulmonary disease,21 but another study of childhood asthma does not confirm this finding.22 To date there have been only a few studies investigating the relation of vitamin D status to lung function in general populations of adults23-25 and adolescents.26 A positive association of serum 25(OH)D with FVC or FEV1 has been demonstrated in the Third National Health and Nutrition Survey in the US23,26 and in the Copenhagen City Heart Study and the Copenhagen General Population Study in Denmark,24 which is not supported by the Hertfordshire Cohort Study in the United Kingdom.25 However, there has been a lack of population-based studies that examine the relationship between vitamin D status and lung function in children. In addition, there has been no epidemiologic study to date examining the association between vitamin D status and FeNO in a population sample of children. The objectives of this study were to investigate the relationship of vitamin D status with lung function and FeNO in a large and well-characterized population-based cohort study of children.
Serum 25(OH)D Serum 25(OH)D levels were measured by a new automated electrochemiluminescence immunoassay, Elecsys Vitamin D total assay (Roche Diagnostics, Mannheim, Germany), in the central laboratory at the Chang Gung Memorial Hospital (Taoyuan, Taiwan), which is accredited by the College of American Pathologists since 2003 with an accuracy-based 25(OH)D survey offered by the College of American Pathologists conducted semiannually. This new assay employs a competitive test principle using recombinant vitamin D binding protein allowing measurement of both 25(OH)D2 and 25(OH)D3, instead of using a monoclonal antibody against 25(OH)D3 in the former Elecsys Vitamin D3 assay that showed underperformance.30 The assay is standardized against liquid-chromatography tandem mass spectrometry with traceability to the National Institute of Standards and Technology standard reference material 972.30 In-house precision testing showed intra-assay coefficients of variation of 3.7% and 3.4% at 15 and 32 ng/mL, respectively, and interassay coefficients of variation of 7.9% and 5.4% at 17 and 33 ng/mL, respectively.
Methods
FeNO and Lung Function The FeNO was measured in all subjects by a single-breath online method using a chemiluminescence analyzer (CLD 88sp nitric oxide [NO] analyzer; Eco Medics, Duernten, Switzerland) according to the 2005 American Thoracic Society/European Respiratory Society guidelines.31 All subjects were requested to avoid eating, drinking, and strenuous exercise 1 hour before the FeNO measurements. Ambient NO and temperature were recorded. Subjects inhaled NO-free air through a mouthpiece of the DENOX 88 NO-free air supply module (EcoMedics, Duernten, Switzerland) over a period of 2-3 seconds to total lung capacity, minimizing contamination of ambient NO. Subjects then exhaled at a flow rate of 50 mL/s and against enough resistance to maintain an oro-pharyngeal pressure of 5-20 cm H2O, thus, preventing contamination of nasal NO. An exhalation time of 12 seconds was used as default, and in children younger than 12 years of age, exhalation time was reduced to 6 seconds if needed. Repeated exhalations were performed for a maximum of 6 attempts to obtain 3 acceptable plateau FeNO values that agreed within 10% or 2 values within 5%. The mean FeNO was recorded. After FeNO measurements, pulmonary function was measured using spirometry (Spirolab II, Medical International Research, Roma, Italy) in accordance with the American Thoracic Society/European Respiratory Society recommendations.32 Three technically acceptable forced expirations were performed for up to 8 tests. The highest FVC, FEV1, PEF, and FEF25-75 were recorded and used in the analyses.
The Prediction of Allergies in Taiwanese Children (PATCH) study is a population-based prospective cohort study that was launched in 2007 in Keelung (25 N latitude), Taiwan, to investigate the epidemiology and predictive factors of asthma and allergies in children. Detailed descriptions of subject recruitment and data collection have been reported previously.8,9,27-29 The subject flow diagram of the current study is presented in Figure 1 (available at www.jpeds. com). Briefly, study subjects were enrolled from a schoolbased sample of 5351 children (2616 boys, 48.9%; age, 10.4 2.9 years) in an International Study of Asthma and Allergies in Childhood epidemiologic survey. A random sample of 1900 subjects were invited to undergo a thorough examination, and 1717 agreed to participate, representing an overall participation rate of 90.4%. Parents of these 1717 study subjects answered a questionnaire regarding demographic data, general health information, and questions related to clinical symptoms and diagnosis of allergic diseases. FeNO measurements and pulmonary function tests were performed, and if parents agreed to blood sampling, blood was collected for serum levels of 25(OH)D. Serum levels of 25(OH)D were measured successfully in 1315 subjects. There was no significant difference in terms of age, sex, and prevalence of allergic diseases between these 1315 subjects who provided blood samples and the original 5351 cohort members, indicating a sampling cohort representative of the general population. All subjects were born to parents who were of Asian descent. The Institutional Review Board of Chang Gung Medical Foundation approved the study (96-0370B). Informed consent was obtained from the parents of all subjects, and assent was obtained from children over 7 years of age. 2
Statistical Analyses All data analyses were performed using the SPSS statistical package version 15.0 for Windows (SPSS, Chicago, Illinois). We categorized serum 25(OH)D levels as being sufficient Yao et al
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when $30 ng/mL, insufficient between 20 and 30 ng/mL, and deficient when <20 ng/mL, as described in the literature.16 Multivariable linear regression was used to examine the relationship of serum 25(OH)D categories with lung function variables and FeNO, adjusted for age, sex, height, body mass index (BMI), season of sampling, and exposure to environmental tobacco smoke. We also examined serum 25(OH) D as a continuous variable in the analysis. Linear trends were tested for significance by regressing lung function measures on serum 25(OH)D levels, with adjustment for the covariates listed above. A P value of <.05 was considered statistically significant.
Results The characteristics of the 1315 subjects are listed in Table I. The average age was 10.3 years (SD, 2.7 years [range 5-18]), and 49.0% of subjects were male. The number (percentage) of subjects who had sufficient ($30 ng/mL), insufficient (20-29.9 ng/mL), and deficient (<20 ng/mL) vitamin D levels was 128 (9.7%), 517 (39.3%), and 670 (51.0%), respectively. Acceptable FeNO measurements and lung function tests were available in 1270 (96.6%) and 1282 (97.5%) subjects, respectively. The prevalence of diagnosed asthma, rhinitis, and eczema in the study population was 11.0%, 37.6%, and 19.6%, respectively. Relationship of Serum 25(OH)D with Lung Function Relationships between serum 25(OH)D categories and lung function variables are shown in Table II. Multivariable regression analysis was undertaken to explore the relationship of serum 25(OH)D categories with lung function, taking factors associated with lung function and serum 25(OH)D into consideration. After adjusting for Table I. Characteristics of study subjects Characteristics
Sample size
Data*
Age, y (mean SD) Sex (male) [n (%)] Male Female Height (cm) (mean SD) BMI, kg/m2 (mean SD) Season of sampling [n (%)] Spring (Mar to May) Summer (Jun to Aug) Autumn (Sep to Nov) Winter (Dec to Feb) Lung function (mean SD) FVC (L) FEV1 (L) FEV1/FVC ratio (%) PEF (L/s) FEF25-75 (L/s) FeNO (p.p.b) (mean SD) Asthma [n (%)] Rhinitis [n (%)] Eczema [n (%)]
1315 1315
10.3 2.7
1315 1315 1315
645 (49.0) 670 (51.0) 138.9 14.8 18.7 3.6 586 (44.6) 206 (15.7) 85 (6.5) 438 (33.3)
1282
1270 1297 1287 1292
p.p.b, parts per billion. *Values are listed as n (%) or mean SD, as appropriate.
2.09 0.67 1.82 0.58 87.3 5.94 3.50 1.11 2.22 0.77 25.9 23.9 143 (11.0) 484 (37.6) 253 (19.6)
Table II. Multivariable analysis of associations of serum 25(OH)D categories with lung function variables and FeNO 25(OH)D (ng/mL) FVC (L) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FEV1 (L) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FEV1/FVC ratio (%) $30 ng/mL 20-29.9 ng/mL <20 ng/mL PEF (L/s) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FEF25-75 (L/s) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FeNO (p.p.b) $30 ng/mL 20-29.9 ng/mL <20 ng/mL
n
b (95% CI)
P
126 504 652
Reference 0.053 ( 0.105, 0.001) 0.082 ( 0.134, 0.030)
.045 .002
126 504 652
Reference 0.048 ( 0.095, 0.002) 0.055 ( 0.102, 0.009)
.042 .020
126 504 652
Reference 0.193 ( 1.329, 0.944) 0.392 ( 0.750, 1.534)
.740 .501
126 504 652
Reference 0.043 ( 0.176, 0.090) 0.078 ( 0.212, 0.056)
.528 .253
126 504 652
Reference 0.032 ( 0.130, 0.066) 0.004 ( 0.102, 0.094)
.525 .936
127 494 649
Reference 0.042 ( 0.114, 0.198) 0.103 ( 0.054, 0.259)
.595 .198
Serum 25(OH)D levels were categorized into 3 ordinal categories of vitamin D status: <20, 2029.9, and $30 ng/mL (reference). Adjusted for age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. P values <.05 are in bold.
age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke, the serum 25(OH)D status was positively and significantly associated with FVC and FEV1 (Table II and Figure 2). Specifically, the mean difference in FVC between the subjects with vitamin D insufficiency and those with sufficient serum 25(OH)D levels was 53.4 mL (SE, 26.5 mL) (P = .045), and the mean difference was 81.9 mL (SE, 26.7 mL) (P = .002) between the subjects with vitamin D deficiency and those with sufficient serum 25(OH)D levels. The mean difference in FEV1 between the subjects with vitamin D insufficiency and those with sufficient serum 25(OH)D levels was 48.2 mL (SE, 23.6 mL) (P = .042), and the mean difference was 55.2 mL (SE, 23.7 mL) (P = .020) between the subjects with vitamin D deficiency and those with sufficient serum 25(OH)D levels. The evidence for association with FVC and FEV1 remained in subgroup analyses stratified by asthma, with greater differences seen in the subgroup of subjects with asthma. There was, however, no significant difference in the FEV1/FVC, PEF, or FEF25-75 between the 3 serum 25(OH)D categories, whether the subjects did or did not have asthma. We also explored the relationship between serum 25(OH) D levels (as a continuous variable) and lung function parameters (Table III). After controlling for confounders, this showed significant positive associations of serum 25(OH)D levels with FVC (P = .001), FEV1 (P = .017), and PEF (P = .041) (Table III). Specifically, there was a 3.6 mL (SE, 1.1 mL) increase in FVC for each nanogram per milliliter increase in serum 25(OH)D level. There was a 2.4 mL (SE,
Serum 25-Hydroxyvitamin D Levels in Relation to Lung Function and Exhaled Nitric Oxide in Children
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Figure 2. A, Adjusted mean (SE) FVC and B, FEV1 by categories of serum 25(OH)D. Adjusted for age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. *P < .05.
1.0 mL) increase in FEV1 for each nanogram per milliliter increase in serum 25(OH)D level. There was a 5.9 mL/s (SE, 2.9 mL/s) increase in PEF for each nanogram per milliliter increase in serum 25(OH)D level. Relationship of Serum 25(OH)D with FeNO Relationships between serum 25(OH)D categories and FeNO are shown in Table II. After adjusting for confounders, serum 25(OH)D status had no association with FeNO (Table II). To further explore the association of serum 25(OH)D with FeNO, we also examined serum 25(OH)D as a continuous variable in the analysis. There was no significant association between serum 25(OH)D levels and FeNO (Table III). Subgroup analyses did not reveal significant associations between vitamin D status and FeNO in the subgroups of subjects with and without asthma.
Discussion There is increasing evidence to suggest an expanded role for vitamin D in health outcomes apart from its classic action on
Table III. Multivariable analysis of associations of serum 25(OH)D levels with lung function variables and FeNO 25(OH)D (ng/mL)
n
FVC (L) FEV1 (L) FEV1/FVC ratio (%) PEF (L/s) FEF25-75 (L/s) FeNO (p.p.b)
1282 1282 1282 1282 1282 1270
b (95% CI) 0.004 (0.001, 0.006) 0.002 (0.001, 0.004) 0.019 ( 0.067, 0.030) 0.006 (0.001, 0.012) 0.001 ( 0.004, 0.005) 0.003 ( 0.010, 0.003)
P .001 .017 .449 .041 .774 .317
Serum 25(OH)D levels were treated as a continuous variable. Adjusted for age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. P values <.05 are in bold.
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skeletal health. Given that vitamin D deficiency has recently been reported as a previously unrecognized common problem in many countries, understanding the adverse impact of vitamin D status on health outcomes has important public health implications. This is a large population-based study addressing the relation of vitamin D to lung function and FeNO in children. The main finding in the present study is that serum vitamin D levels are positively and independently associated with lung function with a suggested dose-response effect, indicating a potentially important role for vitamin D in respiratory health. These associations are independent of several potential confounding factors, such as age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. Another important finding is that vitamin D status is not related to FeNO in children in the general population. To our knowledge, there is a lack of published data on the relation between vitamin D status and lung function in children in the general population. Our findings present new evidence that children with higher serum vitamin D levels have better lung function at a population level, extending the findings from previous studies that have reported a positive relationship between serum 25(OH)D and FVC or FEV1 in the general population of adults and adolescents in the US23,26 and adults in Denmark.24 Our findings are in accordance with the findings from recent studies of adults17,18 and children19,20 with asthma, in which vitamin D levels were also positively associated with lung function. After adjustment for confounding factors, the mean difference in FVC and FEV1 between subjects with insufficient and sufficient serum 25(OH)D levels was 53.4 and 48.2 mL, respectively. These increased to 81.9 and 55.2 mL for FVC and FEV1, respectively, when the subjects with deficient and sufficient levels were compared. In other words, an increase of 1 ng/mL in serum 25(OH)D was associated with an increase in both FVC of 3.6 mL and FEV1 of 2.4 mL. The dose-response Yao et al
- 2014 relationship described strengthens the observations in the current study, although causality between vitamin D levels and lung function cannot be determined in an observational study. Although the exact mechanisms underlying the connection between vitamin D status and lung function remains unclear at present, one possibility is that vitamin D improves lung function through its influence on airway remodeling by affecting smooth muscle cell movement, growth, and contractility and by inhibiting matrix metalloproteinase and fibroblast proliferation.33,34 Other plausible mechanisms include the action of vitamin D on regulating inflammation35-38 and modulating risk of respiratory infections.39,40 In addition, there have been animal models demonstrating an important role of vitamin D in lung development and maturation in utero and in the immediate postpartum period,41,42 further supporting the link between vitamin D and lung function in children. It is interesting to note that vitamin D status is simultaneously associated with FVC and FEV1, but not with FEV1/FVC and FEF25-75, both of which are primarily used as measures of airway obstruction. The reasons for this discrepancy remain unclear, although one might speculate that the impact of vitamin D on lung function may be mediated through changes in total lung capacity, which will affect both FVC and FEV1, rather than mediated through airway obstruction. In the meantime, however, we cannot totally exclude the possibility that the apparent effect of vitamin D status on lung function may actually reflect the simultaneous influence of physical activity (in this case, outdoor activity in particular) on lung function and vitamin D levels through sun exposure. It would be quite interesting to investigate whether vitamin D supplementation confers any benefits in improving lung function in atrisk children in a longitudinal study. This may also address the issue as to whether there is a causal relationship between vitamin D status and lung function. Emerging data suggests that vitamin D has a potential role in regulating inflammation.35-38 It is, therefore, possible that serum vitamin D levels may influence airway inflammation. In this population-based study, however, we did not observe a significant association between serum 25(OH)D and airway inflammation, as measured by FeNO levels, after controlling for confounding factors. This finding suggests that vitamin D may not be a significant determinant of FeNO and may not contribute to promotion of eosinophilic airway inflammation in the general population. This study has several strengths, including the representative sampling of children across a broad age range in the community, large sample size with robust data collection, and incorporation of objective measures of lung function and FeNO. The relatively large sample size of this study had sufficient statistical power for the sets of predictors to explain a significant proportion of variance of lung function and FeNO, (ie, 100% power at a 2-sided type 1 error rate of 5% in the multiple linear regression models). This study has some limitations. A major limitation of this study is its cross-sectional design, which precludes our ability to make
ORIGINAL ARTICLES causal inferences about the observed associations. Longitudinal follow-up of the cohort subjects is currently underway, which may help to elucidate a clearer relationship between vitamin D and lung function. In addition, there is a lack of data on dietary and supplemental vitamin D intake in this study. Furthermore, it is not clear whether the results in this population of Asian children in Taiwan are generalizable to other populations. In conclusion, this population-based study demonstrates evidence for a relationship between insufficient vitamin D levels and worse lung function in children in the community with a suggested dose-response effect. Our findings also suggest that vitamin D status is not a significant determinant of FeNO in children in the general population. n We thank the study subjects, their parents, their teachers, and the school nurses, as well as the schools involved, for their active participation in the study. We also thank the Department of Education, Keelung City Government, Keelung City, Taiwan, for administrative support for the study. Submitted for publication May 9, 2014; last revision received Jul 18, 2014; accepted Aug 22, 2014. Reprint requests: Tsung-Chieh Yao, MD, PhD and Jing-Long Huang, MD, Division of Allergy, Asthma, and Rheumatology, Department of Pediatrics, Chang Gung Memorial Hospital, 5, Fu-Hsin St, Kweishan, Taoyuan, Taiwan. E-mail: [email protected] and [email protected]
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12. Latzin P, Beck J, Griese M. Exhaled nitric oxide in healthy children: variability and a lack of correlation with atopy. Pediatr Allergy Immunol 2002;13:37-46. 13. Wong GW, Liu EK, Leung TF, Yung E, Ko FW, Hui DS, et al. High levels and gender difference of exhaled nitric oxide in Chinese schoolchildren. Clin Exp Allergy 2005;35:889-93. 14. Linn WS, Rappaport EB, Berhane KT, Bastain TM, Avol EL, Gilliland FD. Exhaled nitric oxide in a population-based study of southern California schoolchildren. Respir Res 2009;10:28. 15. Kovesi T, Kulka R, Dales R. Exhaled nitric oxide concentration is affected by age, height, and race in healthy 9- to 12-year-old children. Chest 2008; 133:169-75. 16. Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81. 17. Sutherland ER, Goleva E, Jackson LP, Stevens AD, Leung DY. Vitamin D levels, lung function, and steroid response in adult asthma. Am J Respir Crit Care Med 2010;181:699-704. 18. Li F, Peng M, Jiang L, Sun Q, Zhang K, Lian F, et al. Vitamin D deficiency is associated with decreased lung function in Chinese adults with asthma. Respiration 2011;81:469-75. 19. Searing DA, Zhang Y, Murphy JR, Hauk PJ, Goleva E, Leung DY. Decreased serum vitamin D levels in children with asthma are associated with increased corticosteroid use. J Allergy Clin Immunol 2010;125:9951000. 20. Gupta A, Sjoukes A, Richards D, Banya W, Hawrylowicz C, Bush A, et al. Relationship between serum vitamin D, disease severity, and airway remodeling in children with asthma. Am J Respir Crit Care Med 2011;184: 1342-9. 21. Janssens W, Bouillon R, Claes B, Carremans C, Lehouck A, Buysschaert I, et al. Vitamin D deficiency is highly prevalent in COPD and correlates with variants in the vitamin D-binding gene. Thorax 2010;65:215-20. 22. Brehm JM, Celedon JC, Soto-Quiros ME, Avila L, Hunninghake GM, Forno E, et al. Serum vitamin D levels and markers of severity of childhood asthma in Costa Rica. Am J Respir Crit Care Med 2009;179:765-71. 23. Black PN, Scragg R. Relationship between serum 25-hydroxyvitamin d and pulmonary function in the third national health and nutrition examination survey. Chest 2005;128:3792-8. 24. Afzal S, Lange P, Bojesen SE, Freiberg JJ, Nordestgaard BG. Plasma 25-hydroxyvitamin D, lung function and risk of chronic obstructive pulmonary disease. Thorax 2014;69:24-31. 25. Shaheen SO, Jameson KA, Robinson SM, Boucher BJ, Syddall HE, Sayer AA, et al. Relationship of vitamin D status to adult lung function and COPD. Thorax 2011;66:692-8. 26. Tolppanen AM, Williams D, Henderson J, Lawlor DA. Serum 25hydroxy-vitamin D and ionised calcium in relation to lung function and allergen skin tests. Eur J Clin Nutr 2011;65:493-500. 27. Yao TC, Ou LS, Yeh KW, Lee WI, Chen LC, Huang JL. Associations of Age, Gender, and BMI with Prevalence of Allergic Diseases in Children: PATCH Study. J Asthma 2011;48:503-10.
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Vol. -, No. 28. Tu YL, Chang SW, Tsai HJ, Chen LC, Lee WI, Hua MC, et al. Total Serum IgE in a population-based study of Asian children in Taiwan: reference value and significance in the diagnosis of allergy. PLoS One 2013;8:e80996. 29. Yao TC, Tsai HJ, Tu YL, Chang SW, Hua MC, Liao SL, et al. Multiplexed immunoglobulin E sensitization in relation to exhaled nitric oxide in a population sample of children. Allergy 2014;69:678-82. 30. Emmen JM, Wielders JP, Boer AK, van den Ouweland JM, Vader HL. The new Roche vitamin D total assay: fit for its purpose? Clin Chem Lab Med 2012;50:1969-72. 31. ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005. Am J Respir Crit Care Med 2005;171:912-30. 32. Miller MR, Hankinson J, Brusasco V, Burgos F, Casaburi R, Coates A, et al. Standardisation of spirometry. Eur Respir J 2005;26:319-38. 33. Damera G, Fogle HW, Lim P, Goncharova EA, Zhao H, Banerjee A, et al. Vitamin D inhibits growth of human airway smooth muscle cells through growth factor-induced phosphorylation of retinoblastoma protein and checkpoint kinase 1. Br J Pharmacol 2009;158:1429-41. 34. Banerjee A, Damera G, Bhandare R, Gu S, Lopez-Boado Y, Panettieri R Jr, et al. Vitamin D and glucocorticoids differentially modulate chemokine expression in human airway smooth muscle cells. Br J Pharmacol 2008;155:84-92. 35. Baeke F, Takiishi T, Korf H, Gysemans C, Mathieu C, Vitamin D. modulator of the immune system. Curr Opin Pharmacol 2010;10:482-96. 36. Searing DA, Leung DY. Vitamin D in atopic dermatitis, asthma and allergic diseases. Immunol Allergy Clin North Am 2010;30:397-409. 37. Mahon BD, Wittke A, Weaver V, Cantorna MT. The targets of vitamin D depend on the differentiation and activation status of CD4 positive T cells. J Cell Biochem 2003;89:922-32. 38. Xystrakis E, Kusumakar S, Boswell S, Peek E, Urry Z, Richards DF, et al. Reversing the defective induction of IL-10-secreting regulatory T cells in glucocorticoid-resistant asthma patients. J Clin Invest 2006;116:146-55. 39. Bozzetto S, Carraro S, Giordano G, Boner A, Baraldi E. Asthma, allergy and respiratory infections: the vitamin D hypothesis. Allergy 2012;67:10-7. 40. Finklea JD, Grossmann RE, Tangpricha V. Vitamin D and chronic lung disease: a review of molecular mechanisms and clinical studies. Adv Nutr 2011;2:244-53. 41. Nguyen M, Trubert CL, Rizk-Rabin M, Rehan VK, Besancon F, Cayre YE, et al. 1,25-Dihydroxyvitamin D3 and fetal lung maturation: immunogold detection of VDR expression in pneumocytes type II cells and effect on fructose 1,6 bisphosphatase. J Steroid Biochem Mol Biol 2004;89-90:93-7. 42. Sakurai R, Shin E, Fonseca S, Sakurai T, Litonjua AA, Weiss ST, et al. 1alpha,25(OH)2D3 and its 3-epimer promote rat lung alveolar epithelialmesenchymal interactions and inhibit lipofibroblast apoptosis. Am J Physiol Lung Cell Mol Physiol 2009;297:L496-505.
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Members of the PATCH Study Group include: Jing-Long Huang, MD (Study Coordinator), Tsung-Chieh Yao, MD, PhD, Wen-I Lee, MD, PhD, Liang-Shiou Ou, MD, Li-Chen Chen, MD, Kuo-Wei Yeh, MD, Yu-Ling Tu, MD, ShenHao Lai, MD (Chang Gung Memorial Hospital, Taoyuan, Taiwan), Man-Chin Hua, MD, Ming-Han Tsai, MD, PhD, and Sui-Ling Liao, MD (Chang Gung Memorial Hospital at Keelung, Keelung, Taiwan) (Principal Investigators).
Figure 1. Schematic presentation of the recruitment process of the study subjects.
Serum 25-Hydroxyvitamin D Levels in Relation to Lung Function and Exhaled Nitric Oxide in Children
6.e1
Study design A total of 1315 children aged 5-18 years were evaluated using serum 25-hydroxyvitamin D [25(OH) D] levels, spirometry, a single-breath online FeNO measurement, and questionnaires.
Results After adjusting for confounders, the mean forced vital capacity was 53.4 mL (SE, 26.5 mL; P = .045), and the mean forced expiratory volume in 1 second was 48.2 mL (SE, 23.6 mL; P = .042) lower for children with insufficient serum 25(OH)D levels (20-29.9 ng/mL) compared with those with sufficient 25(OH)D levels ($30 ng/mL). The mean difference between children with deficient (<20 ng/mL) and sufficient levels of serum 25(OH)D was 81.9 mL (SE, 26.7 mL; P = .002) for forced vital capacity and 55.2 mL (SE, 23.7 mL; P = .020) for forced expiratory volume in 1 second. There was no significant association between serum 25(OH)D levels and FeNO after adjusting for confounders. Conclusions Our results demonstrate a significant relationship between insufficient serum vitamin D levels and worse lung function in children in the community with a suggested dose-response effect. Our findings also suggest that vitamin D status is not a significant determinant of FeNO in children in the general population. (J Pediatr 2014;-:---).
L
ung function, as assessed by the spirometric measures of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), the FEV1 to FVC ratio (FEV1/FVC), peak expiratory flow (PEF), and forced expiratory flow at 25%-75% (FEF25-75), is an objective indicator of general respiratory health. Lung development peaks between the ages of 20 and 25 years, is stable for 5-10 years, and then declines with increasing age.1 Mild perturbations in lung function, which may not be clinically apparent, have been shown to be an important long-term predictor of all-cause mortality and morbidity.2-6 Although variation in lung function between individuals is in part genetically determined,7 a significant proportion of the variation in lung function remains unexplained. The fraction of exhaled nitric oxide (FeNO) is a noninvasive biomarker of From the Division of Allergy, Asthma, and airway inflammation. We have demonstrated that FeNO discriminates children Rheumatology, Department of Pediatrics, Chang Gung with and without allergic sensitization independent of allergic symptoms in a Memorial Hospital and Chang Gung University College of Medicine, Taoyuan, Taiwan; Community Medicine population-based study.8 Although previous studies by our group8,9 and Research Center, Chang Gung Memorial Hospital at 10-15 Keelung, Keelung, Taiwan; Graduate Institute of Clinical others have identified important determinants of FeNO, the variation in Medical Sciences and Clinical Informatics and Medical FeNO levels at the population level remains partially unknown. Statistics Research Center, Chang Gung University College of Medicine, Taoyuan, Taiwan; Division of In addition to its historically well-known effects on calcium homeostasis and Biostatistics and Bioinformatics, Institutes of Population Health Sciences, National Health Research Institutes, bone metabolism, vitamin D is now recognized to play a role in the immune sysMiaoli, Taiwan; Department of Pediatrics, Feinberg 16 School of Medicine, Northwestern University, Chicago, tem, cardiovascular system, and cancer prevention. Recently, a few studies have IL; Department of Genome Medicine, Kaohsiung investigated the relationship of vitamin D to lung function in individuals with lung University, Kaohsiung, Taiwan; Department of Laboratory Medicine, Chang Gung Memorial Hospital, diseases, although the results have been conflicting. Some studies have found posTaoyuan, Taiwan; Department of Pediatrics, Chang Gung Memorial Hospital at Keelung, Keelung, Taiwan; itive associations between serum 25-hydroxyvitamin D [25(OH)D] levels and lung 1
2
3
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and 10Division of Pediatric Pulmonology, Department of Pediatrics, Chang Gung Memorial Hospital, Taoyuan, Taiwan
25(OH)D BMI FEF25-75 FeNO FEV1 FVC NO PEF
25-hydroxyvitamin D Body mass index Forced expiratory flow at 25%-75% Fraction of exhaled nitric oxide Forced expiratory volume in 1 second Forced vital capacity Nitric oxide Peak expiratory flow
*List of members of the PATCH Study Group is available at www.jpeds.com (Appendix). Supported by the National Science Council Taiwan (101-2314-B-182A-044, 102-2314-B-182A-048, and 101-2314-B-400-009-MY2) and Chang Gung Memorial Hospital (CMRPG260291260293, CMRPG2B00712B0073, and CMRPG4B00314B0033). The authors declare no conflicts of interest. 0022-3476/$ - see front matter. Copyright ª 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jpeds.2014.08.048
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function in adults17,18 and children19,20 with asthma and in patients with chronic obstructive pulmonary disease,21 but another study of childhood asthma does not confirm this finding.22 To date there have been only a few studies investigating the relation of vitamin D status to lung function in general populations of adults23-25 and adolescents.26 A positive association of serum 25(OH)D with FVC or FEV1 has been demonstrated in the Third National Health and Nutrition Survey in the US23,26 and in the Copenhagen City Heart Study and the Copenhagen General Population Study in Denmark,24 which is not supported by the Hertfordshire Cohort Study in the United Kingdom.25 However, there has been a lack of population-based studies that examine the relationship between vitamin D status and lung function in children. In addition, there has been no epidemiologic study to date examining the association between vitamin D status and FeNO in a population sample of children. The objectives of this study were to investigate the relationship of vitamin D status with lung function and FeNO in a large and well-characterized population-based cohort study of children.
Serum 25(OH)D Serum 25(OH)D levels were measured by a new automated electrochemiluminescence immunoassay, Elecsys Vitamin D total assay (Roche Diagnostics, Mannheim, Germany), in the central laboratory at the Chang Gung Memorial Hospital (Taoyuan, Taiwan), which is accredited by the College of American Pathologists since 2003 with an accuracy-based 25(OH)D survey offered by the College of American Pathologists conducted semiannually. This new assay employs a competitive test principle using recombinant vitamin D binding protein allowing measurement of both 25(OH)D2 and 25(OH)D3, instead of using a monoclonal antibody against 25(OH)D3 in the former Elecsys Vitamin D3 assay that showed underperformance.30 The assay is standardized against liquid-chromatography tandem mass spectrometry with traceability to the National Institute of Standards and Technology standard reference material 972.30 In-house precision testing showed intra-assay coefficients of variation of 3.7% and 3.4% at 15 and 32 ng/mL, respectively, and interassay coefficients of variation of 7.9% and 5.4% at 17 and 33 ng/mL, respectively.
Methods
FeNO and Lung Function The FeNO was measured in all subjects by a single-breath online method using a chemiluminescence analyzer (CLD 88sp nitric oxide [NO] analyzer; Eco Medics, Duernten, Switzerland) according to the 2005 American Thoracic Society/European Respiratory Society guidelines.31 All subjects were requested to avoid eating, drinking, and strenuous exercise 1 hour before the FeNO measurements. Ambient NO and temperature were recorded. Subjects inhaled NO-free air through a mouthpiece of the DENOX 88 NO-free air supply module (EcoMedics, Duernten, Switzerland) over a period of 2-3 seconds to total lung capacity, minimizing contamination of ambient NO. Subjects then exhaled at a flow rate of 50 mL/s and against enough resistance to maintain an oro-pharyngeal pressure of 5-20 cm H2O, thus, preventing contamination of nasal NO. An exhalation time of 12 seconds was used as default, and in children younger than 12 years of age, exhalation time was reduced to 6 seconds if needed. Repeated exhalations were performed for a maximum of 6 attempts to obtain 3 acceptable plateau FeNO values that agreed within 10% or 2 values within 5%. The mean FeNO was recorded. After FeNO measurements, pulmonary function was measured using spirometry (Spirolab II, Medical International Research, Roma, Italy) in accordance with the American Thoracic Society/European Respiratory Society recommendations.32 Three technically acceptable forced expirations were performed for up to 8 tests. The highest FVC, FEV1, PEF, and FEF25-75 were recorded and used in the analyses.
The Prediction of Allergies in Taiwanese Children (PATCH) study is a population-based prospective cohort study that was launched in 2007 in Keelung (25 N latitude), Taiwan, to investigate the epidemiology and predictive factors of asthma and allergies in children. Detailed descriptions of subject recruitment and data collection have been reported previously.8,9,27-29 The subject flow diagram of the current study is presented in Figure 1 (available at www.jpeds. com). Briefly, study subjects were enrolled from a schoolbased sample of 5351 children (2616 boys, 48.9%; age, 10.4 2.9 years) in an International Study of Asthma and Allergies in Childhood epidemiologic survey. A random sample of 1900 subjects were invited to undergo a thorough examination, and 1717 agreed to participate, representing an overall participation rate of 90.4%. Parents of these 1717 study subjects answered a questionnaire regarding demographic data, general health information, and questions related to clinical symptoms and diagnosis of allergic diseases. FeNO measurements and pulmonary function tests were performed, and if parents agreed to blood sampling, blood was collected for serum levels of 25(OH)D. Serum levels of 25(OH)D were measured successfully in 1315 subjects. There was no significant difference in terms of age, sex, and prevalence of allergic diseases between these 1315 subjects who provided blood samples and the original 5351 cohort members, indicating a sampling cohort representative of the general population. All subjects were born to parents who were of Asian descent. The Institutional Review Board of Chang Gung Medical Foundation approved the study (96-0370B). Informed consent was obtained from the parents of all subjects, and assent was obtained from children over 7 years of age. 2
Statistical Analyses All data analyses were performed using the SPSS statistical package version 15.0 for Windows (SPSS, Chicago, Illinois). We categorized serum 25(OH)D levels as being sufficient Yao et al
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when $30 ng/mL, insufficient between 20 and 30 ng/mL, and deficient when <20 ng/mL, as described in the literature.16 Multivariable linear regression was used to examine the relationship of serum 25(OH)D categories with lung function variables and FeNO, adjusted for age, sex, height, body mass index (BMI), season of sampling, and exposure to environmental tobacco smoke. We also examined serum 25(OH) D as a continuous variable in the analysis. Linear trends were tested for significance by regressing lung function measures on serum 25(OH)D levels, with adjustment for the covariates listed above. A P value of <.05 was considered statistically significant.
Results The characteristics of the 1315 subjects are listed in Table I. The average age was 10.3 years (SD, 2.7 years [range 5-18]), and 49.0% of subjects were male. The number (percentage) of subjects who had sufficient ($30 ng/mL), insufficient (20-29.9 ng/mL), and deficient (<20 ng/mL) vitamin D levels was 128 (9.7%), 517 (39.3%), and 670 (51.0%), respectively. Acceptable FeNO measurements and lung function tests were available in 1270 (96.6%) and 1282 (97.5%) subjects, respectively. The prevalence of diagnosed asthma, rhinitis, and eczema in the study population was 11.0%, 37.6%, and 19.6%, respectively. Relationship of Serum 25(OH)D with Lung Function Relationships between serum 25(OH)D categories and lung function variables are shown in Table II. Multivariable regression analysis was undertaken to explore the relationship of serum 25(OH)D categories with lung function, taking factors associated with lung function and serum 25(OH)D into consideration. After adjusting for Table I. Characteristics of study subjects Characteristics
Sample size
Data*
Age, y (mean SD) Sex (male) [n (%)] Male Female Height (cm) (mean SD) BMI, kg/m2 (mean SD) Season of sampling [n (%)] Spring (Mar to May) Summer (Jun to Aug) Autumn (Sep to Nov) Winter (Dec to Feb) Lung function (mean SD) FVC (L) FEV1 (L) FEV1/FVC ratio (%) PEF (L/s) FEF25-75 (L/s) FeNO (p.p.b) (mean SD) Asthma [n (%)] Rhinitis [n (%)] Eczema [n (%)]
1315 1315
10.3 2.7
1315 1315 1315
645 (49.0) 670 (51.0) 138.9 14.8 18.7 3.6 586 (44.6) 206 (15.7) 85 (6.5) 438 (33.3)
1282
1270 1297 1287 1292
p.p.b, parts per billion. *Values are listed as n (%) or mean SD, as appropriate.
2.09 0.67 1.82 0.58 87.3 5.94 3.50 1.11 2.22 0.77 25.9 23.9 143 (11.0) 484 (37.6) 253 (19.6)
Table II. Multivariable analysis of associations of serum 25(OH)D categories with lung function variables and FeNO 25(OH)D (ng/mL) FVC (L) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FEV1 (L) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FEV1/FVC ratio (%) $30 ng/mL 20-29.9 ng/mL <20 ng/mL PEF (L/s) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FEF25-75 (L/s) $30 ng/mL 20-29.9 ng/mL <20 ng/mL FeNO (p.p.b) $30 ng/mL 20-29.9 ng/mL <20 ng/mL
n
b (95% CI)
P
126 504 652
Reference 0.053 ( 0.105, 0.001) 0.082 ( 0.134, 0.030)
.045 .002
126 504 652
Reference 0.048 ( 0.095, 0.002) 0.055 ( 0.102, 0.009)
.042 .020
126 504 652
Reference 0.193 ( 1.329, 0.944) 0.392 ( 0.750, 1.534)
.740 .501
126 504 652
Reference 0.043 ( 0.176, 0.090) 0.078 ( 0.212, 0.056)
.528 .253
126 504 652
Reference 0.032 ( 0.130, 0.066) 0.004 ( 0.102, 0.094)
.525 .936
127 494 649
Reference 0.042 ( 0.114, 0.198) 0.103 ( 0.054, 0.259)
.595 .198
Serum 25(OH)D levels were categorized into 3 ordinal categories of vitamin D status: <20, 2029.9, and $30 ng/mL (reference). Adjusted for age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. P values <.05 are in bold.
age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke, the serum 25(OH)D status was positively and significantly associated with FVC and FEV1 (Table II and Figure 2). Specifically, the mean difference in FVC between the subjects with vitamin D insufficiency and those with sufficient serum 25(OH)D levels was 53.4 mL (SE, 26.5 mL) (P = .045), and the mean difference was 81.9 mL (SE, 26.7 mL) (P = .002) between the subjects with vitamin D deficiency and those with sufficient serum 25(OH)D levels. The mean difference in FEV1 between the subjects with vitamin D insufficiency and those with sufficient serum 25(OH)D levels was 48.2 mL (SE, 23.6 mL) (P = .042), and the mean difference was 55.2 mL (SE, 23.7 mL) (P = .020) between the subjects with vitamin D deficiency and those with sufficient serum 25(OH)D levels. The evidence for association with FVC and FEV1 remained in subgroup analyses stratified by asthma, with greater differences seen in the subgroup of subjects with asthma. There was, however, no significant difference in the FEV1/FVC, PEF, or FEF25-75 between the 3 serum 25(OH)D categories, whether the subjects did or did not have asthma. We also explored the relationship between serum 25(OH) D levels (as a continuous variable) and lung function parameters (Table III). After controlling for confounders, this showed significant positive associations of serum 25(OH)D levels with FVC (P = .001), FEV1 (P = .017), and PEF (P = .041) (Table III). Specifically, there was a 3.6 mL (SE, 1.1 mL) increase in FVC for each nanogram per milliliter increase in serum 25(OH)D level. There was a 2.4 mL (SE,
Serum 25-Hydroxyvitamin D Levels in Relation to Lung Function and Exhaled Nitric Oxide in Children
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Figure 2. A, Adjusted mean (SE) FVC and B, FEV1 by categories of serum 25(OH)D. Adjusted for age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. *P < .05.
1.0 mL) increase in FEV1 for each nanogram per milliliter increase in serum 25(OH)D level. There was a 5.9 mL/s (SE, 2.9 mL/s) increase in PEF for each nanogram per milliliter increase in serum 25(OH)D level. Relationship of Serum 25(OH)D with FeNO Relationships between serum 25(OH)D categories and FeNO are shown in Table II. After adjusting for confounders, serum 25(OH)D status had no association with FeNO (Table II). To further explore the association of serum 25(OH)D with FeNO, we also examined serum 25(OH)D as a continuous variable in the analysis. There was no significant association between serum 25(OH)D levels and FeNO (Table III). Subgroup analyses did not reveal significant associations between vitamin D status and FeNO in the subgroups of subjects with and without asthma.
Discussion There is increasing evidence to suggest an expanded role for vitamin D in health outcomes apart from its classic action on
Table III. Multivariable analysis of associations of serum 25(OH)D levels with lung function variables and FeNO 25(OH)D (ng/mL)
n
FVC (L) FEV1 (L) FEV1/FVC ratio (%) PEF (L/s) FEF25-75 (L/s) FeNO (p.p.b)
1282 1282 1282 1282 1282 1270
b (95% CI) 0.004 (0.001, 0.006) 0.002 (0.001, 0.004) 0.019 ( 0.067, 0.030) 0.006 (0.001, 0.012) 0.001 ( 0.004, 0.005) 0.003 ( 0.010, 0.003)
P .001 .017 .449 .041 .774 .317
Serum 25(OH)D levels were treated as a continuous variable. Adjusted for age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. P values <.05 are in bold.
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skeletal health. Given that vitamin D deficiency has recently been reported as a previously unrecognized common problem in many countries, understanding the adverse impact of vitamin D status on health outcomes has important public health implications. This is a large population-based study addressing the relation of vitamin D to lung function and FeNO in children. The main finding in the present study is that serum vitamin D levels are positively and independently associated with lung function with a suggested dose-response effect, indicating a potentially important role for vitamin D in respiratory health. These associations are independent of several potential confounding factors, such as age, sex, height, BMI, season of sampling, and exposure to environmental tobacco smoke. Another important finding is that vitamin D status is not related to FeNO in children in the general population. To our knowledge, there is a lack of published data on the relation between vitamin D status and lung function in children in the general population. Our findings present new evidence that children with higher serum vitamin D levels have better lung function at a population level, extending the findings from previous studies that have reported a positive relationship between serum 25(OH)D and FVC or FEV1 in the general population of adults and adolescents in the US23,26 and adults in Denmark.24 Our findings are in accordance with the findings from recent studies of adults17,18 and children19,20 with asthma, in which vitamin D levels were also positively associated with lung function. After adjustment for confounding factors, the mean difference in FVC and FEV1 between subjects with insufficient and sufficient serum 25(OH)D levels was 53.4 and 48.2 mL, respectively. These increased to 81.9 and 55.2 mL for FVC and FEV1, respectively, when the subjects with deficient and sufficient levels were compared. In other words, an increase of 1 ng/mL in serum 25(OH)D was associated with an increase in both FVC of 3.6 mL and FEV1 of 2.4 mL. The dose-response Yao et al
- 2014 relationship described strengthens the observations in the current study, although causality between vitamin D levels and lung function cannot be determined in an observational study. Although the exact mechanisms underlying the connection between vitamin D status and lung function remains unclear at present, one possibility is that vitamin D improves lung function through its influence on airway remodeling by affecting smooth muscle cell movement, growth, and contractility and by inhibiting matrix metalloproteinase and fibroblast proliferation.33,34 Other plausible mechanisms include the action of vitamin D on regulating inflammation35-38 and modulating risk of respiratory infections.39,40 In addition, there have been animal models demonstrating an important role of vitamin D in lung development and maturation in utero and in the immediate postpartum period,41,42 further supporting the link between vitamin D and lung function in children. It is interesting to note that vitamin D status is simultaneously associated with FVC and FEV1, but not with FEV1/FVC and FEF25-75, both of which are primarily used as measures of airway obstruction. The reasons for this discrepancy remain unclear, although one might speculate that the impact of vitamin D on lung function may be mediated through changes in total lung capacity, which will affect both FVC and FEV1, rather than mediated through airway obstruction. In the meantime, however, we cannot totally exclude the possibility that the apparent effect of vitamin D status on lung function may actually reflect the simultaneous influence of physical activity (in this case, outdoor activity in particular) on lung function and vitamin D levels through sun exposure. It would be quite interesting to investigate whether vitamin D supplementation confers any benefits in improving lung function in atrisk children in a longitudinal study. This may also address the issue as to whether there is a causal relationship between vitamin D status and lung function. Emerging data suggests that vitamin D has a potential role in regulating inflammation.35-38 It is, therefore, possible that serum vitamin D levels may influence airway inflammation. In this population-based study, however, we did not observe a significant association between serum 25(OH)D and airway inflammation, as measured by FeNO levels, after controlling for confounding factors. This finding suggests that vitamin D may not be a significant determinant of FeNO and may not contribute to promotion of eosinophilic airway inflammation in the general population. This study has several strengths, including the representative sampling of children across a broad age range in the community, large sample size with robust data collection, and incorporation of objective measures of lung function and FeNO. The relatively large sample size of this study had sufficient statistical power for the sets of predictors to explain a significant proportion of variance of lung function and FeNO, (ie, 100% power at a 2-sided type 1 error rate of 5% in the multiple linear regression models). This study has some limitations. A major limitation of this study is its cross-sectional design, which precludes our ability to make
ORIGINAL ARTICLES causal inferences about the observed associations. Longitudinal follow-up of the cohort subjects is currently underway, which may help to elucidate a clearer relationship between vitamin D and lung function. In addition, there is a lack of data on dietary and supplemental vitamin D intake in this study. Furthermore, it is not clear whether the results in this population of Asian children in Taiwan are generalizable to other populations. In conclusion, this population-based study demonstrates evidence for a relationship between insufficient vitamin D levels and worse lung function in children in the community with a suggested dose-response effect. Our findings also suggest that vitamin D status is not a significant determinant of FeNO in children in the general population. n We thank the study subjects, their parents, their teachers, and the school nurses, as well as the schools involved, for their active participation in the study. We also thank the Department of Education, Keelung City Government, Keelung City, Taiwan, for administrative support for the study. Submitted for publication May 9, 2014; last revision received Jul 18, 2014; accepted Aug 22, 2014. Reprint requests: Tsung-Chieh Yao, MD, PhD and Jing-Long Huang, MD, Division of Allergy, Asthma, and Rheumatology, Department of Pediatrics, Chang Gung Memorial Hospital, 5, Fu-Hsin St, Kweishan, Taoyuan, Taiwan. E-mail: [email protected] and [email protected]
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ORIGINAL ARTICLES Appendix
Members of the PATCH Study Group include: Jing-Long Huang, MD (Study Coordinator), Tsung-Chieh Yao, MD, PhD, Wen-I Lee, MD, PhD, Liang-Shiou Ou, MD, Li-Chen Chen, MD, Kuo-Wei Yeh, MD, Yu-Ling Tu, MD, ShenHao Lai, MD (Chang Gung Memorial Hospital, Taoyuan, Taiwan), Man-Chin Hua, MD, Ming-Han Tsai, MD, PhD, and Sui-Ling Liao, MD (Chang Gung Memorial Hospital at Keelung, Keelung, Taiwan) (Principal Investigators).
Figure 1. Schematic presentation of the recruitment process of the study subjects.
Serum 25-Hydroxyvitamin D Levels in Relation to Lung Function and Exhaled Nitric Oxide in Children
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