- Email: [email protected]
Determination of serum 25-hydroxyvitamin D3 levels in early postmenopausal Iranian women: relationship with bone mineral density
Bone Vol. 29, No. 5 November 2001:428 – 430
Determination of Serum 25-Hydroxyvitamin D3 Levels in Early Postmenopausal Iranian Women: Relationship With Bone Mineral Density A. RASSOULI,1 I. MILANIAN,1 and M. MOSLEMI-ZADEH2 1 2
Department of Pharmacology, Iran University of Medical Sciences, Tehran, Iran Department of Rheumatology, Loghman-Hakim Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
postmenopausal women have been controversial,3,6,9,10 we performed this preliminary study to determine vitamin D status in early postmenopausal women living in Tehran and the correlation between 25-OHD3 and BMD in the lumbar spine and hip regions.
Serum levels of 25-hydroxyvitamin D3 (25-OHD3) and bone mineral density (BMD) were determined in 73 selected, early postmenopausal women referred to the Bone Densitometry Center, Loghman-Hakim Hospital, Tehran, Iran. The relationship between them was also assessed. 25-OHD3 levels were measured using high-performance liquid chromatography. BMD was measured with dual-energy X-ray absorptiometry of the lumbar spine and proximal femur regions. 25-OHD3 levels ranged from 3.8 to 64.0 ng/mL (mean ⴞ SD: 17.1 ⴞ 11.3). Twenty-six subjects (36%) were vitamin Ddeficient (<12 ng/mL). In the lumbar spine (L2– 4) BMD measurements, 28 subjects (38%) were normal (T score > ⴚ1), 26 (36%) were osteopenic (T < ⴚ1 to >ⴚ2.5), and 19 (26%) were osteoporotic (T < ⴚ2.5). In the hip (total) BMD measurements, 41 subjects (56.1%) were normal, 31 (42.5%) were osteopenic, and 1 (1.4%) was osteoporotic. There was a significant correlation between spine BMD (Z score) and 25-OHD3 (r ⴝ 0.23, p < 0.05), but the correlation was not significant for hip BMD. It was concluded that vitamin D deficiency was evident in early postmenopausal Iranian women, and serum 25-OHD3 was weakly correlated with spine BMD, which may have physiological significance. (Bone 29:428 – 430; 2001) © 2001 by Elsevier Science Inc. All rights reserved.
Materials and Methods Subjects The group studied included 73 early postmenopausal women. They had been selected from a group of 507 early postmenopausal women (within 10 years since menopause) referred to the outpatient Bone Densitometry Center (Loghman-Hakim Hospital, Tehran, Iran) during February to June 2000. All subjects were referred to this center for osteoporosis risk factors, including menopause. Study inclusion criteria were: (1) early postmenopausal status (i.e., 6 months to 10 years since menopause); and (2) residence in Tehran for ⱖ5 years. Exclusion criteria included having a history of: (1) taking drugs known to influence bone metabolism in the past 5 years, such as vitamin D, calcium, corticosteroids, and hormone replacement therapy; (2) musclo skeletal, thyroid, parathyroid, adrenal, hepatic, or renal disease; (3) malignancy; (4) fracture; and (5) hysterectomy. At the time of BMD measurements, the height and weight of the subjects were measured. Moreover, inquiries were made with regard to parity and dietary habits (food frequency).
Key Words: Vitamin D; Bone mineral density (BMD); Menopause; Iran and osteoporosis. Introduction
BMD Measurements
Osteoporosis is an important public health concern, particularly in postmenopausal women.4,9,11 It can be assessed indirectly through a noninvasive measurement of bone mineral density (BMD).9,11 Nevertheless, subclinical vitamin D deficiency, although not sufficient to cause osteomalacia, may lead to secondary hyperparathyroidism and bone loss.8,13 The serum level of 25-dihydroxyvitamin D3 (25-OHD) has been accepted as an index for vitamin D status.1,2,5,14 Because there have been no reports on vitamin D status among the Iranian population, and the data on the relationship between vitamin D status and BMD in
BMD of the lumbar spine (L2– 4, anteroposterior view) and hip (left proximal femur, total) were measured by dual-energy X-ray absorptiometry with a Lunar DPX densitometer. Both T and Z scores were obtained. In the T-score calculations, the manufacturer’s ranges for a USA reference population were used. For Z-score calculations, the manufacturer’s reference data were used for age, weight, and ethnic origin (Asian) adjustments of BMD. Blood Collection and Storage Nonfasting blood samples were collected for biochemical tests at the time of BMD measurements. The sera of the blood samples were separated, divided in small portions, and frozen at ⫺20°C. The sera were analyzed within 2– 4 weeks after sampling.
Address for correspondence and reprints: Dr. Iraj Milanian, Department of Pharmacology, Iran University of Medical Sciences, P.O. Box 141556183, Tehran, Iran. E-mail: [email protected]. © 2001 by Elsevier Science Inc. All rights reserved.
428
8756-3282/01/$20.00 S8756-3282(01)00591-9
Bone Vol. 29, No. 5 November 2001:428 – 430
Biochemical Tests Serum calcium (Ca), phosphorus (P), creatinine (Cr), urea, albumin (Alb), and alkaline phosphatase (ALP) were measured with an RA 1000 autoanalyzer (Technicon). Serum 25-OHD3 levels were measured using a modified high-performance liquid chromatography (HPLC).1 The modification included use of an internal standard (nandrolone decanoate) and changing the mobile phase to methanol:isopropanol:water at 60:28:12. The intraand interassay coefficients of variations were ⬍8% and ⬍10%, respectively. The detection limit was 2.5 ng/mL. Dietary Data Analysis Average daily dietary intakes of vitamin D, calcium, phosphorus, and fiber for the subjects were determined with the assistance of a trained dietitian. Data were obtained using a technique that scores only foods containing considerable levels of these compounds, as determined by nutritional information from the USDA and Canadian NF. Statistical Analysis All data were expressed as mean ⫾ SD. Partial correlation coefficients of variables controlling for age were used to determine the association between variables. For evaluation of the relationship between BMD and other variables, except for age, Z score was used. Means were compared by Student’s t-test. Statistical analyses were performed using SPSS for WINDOWS, release 9.0 (SPSS, Inc.). All probability values were based on two-tailed tests, and p ⬍ 0.05 was considered significant. Whenever data departed substantially from a normal distribution, data transformations were made. Results Distribution characteristics of age, time since menopause, serum 25-OHD3 spine and hip BMD, parity, body mass index (BMI), daily dietary intakes (vitamin D, calcium, phosphorus, and fiber), as well as certain measured serum parameters are summarized in Table 1. Twenty-six subjects (36%) had 25-OHD3 levels of ⬍12 ng/mL. For lumbar spine BMD measurements (T score), 28 subjects (38%) were normal, 26 (36%) were osteopenic, and 19 (26%) were osteoporotic. For hip BMD measurements (T score), 41 subjects (56.1%) were normal, 31 (42.5%) were osteopenic, and 1 (1.4%) was osteoporotic. There was no significant difference between serum 25-OHD3 levels collected in winter (13.3 ⫾ 5.0 ng/mL, n ⫽ 17) and spring (18.3 ⫾ 12 ng/mL, n ⫽ 56). There was a significant correlation between spine BMD (Z score) and 25-OHD3 (r ⫽ 0.23), but for hip BMD the correlation was not significant. There were also no significant correlations between age and 25-OHD3 as well as spine and hip BMD. Time since menopause had a significant correlation only with spine BMD (r ⫽ ⫺0.38). Serum ALP had significant correlations with 25-OHD3 (r ⫽ ⫺0.27), spine BMD (r ⫽ ⫺0.28), and hip BMD (r ⫽ ⫺0.25). Parity has a significant correlation only with spine BMD (r ⫽ ⫺0.24). Other measured serum and dietary parameters had no significant correlations with 25-OHD3 or spine and hip BMD. Discussion The most important finding of this study is that 26 subjects (36%) were vitamin D-deficient. These subjects had 25-OHD3 levels of ⬍12 ng/mL (30 nmol/L), despite ample sunshine
A. Rassouli et al. Vitamin D and BMD in Iranian women
429
Table 1. Distribution characteristics of age, time since menopause (TSM), serum 25-hydroxyvitamin D3 (25-OHD3), spine and hip bone mineral density (BMD), parity, body mass index (BMI), serum calcium (Ca), phosphorus (P), Albumin (Alb), alkaline phosphatase (ALP), urea, and creatinine (Cr), and daily dietary intakes of vitamin D, Ca, and fiber in 73 early postmenopausal Iranian women Variable Age (years) TSM (year) 25-OHD3 (ng/mL)a Spine BMD (g/cm2) Hip BMD (g/cm2) Parity (n) BMI (kg/m2) Ca (mg/dL) P (mg/dL) Alb (g/dL)a ALP (U/L)a Urea (mg/dL) Cr (mg/dL) Vitamin D intake (IU)a Ca intake (mg) Fiber intake (g) a
Mean ⫾ SD
Range
55.7 ⫾ 3.6 4.9 ⫾ 3.1 17.1 ⫾ 11.3 1.018 ⫾ 0.143 0.917 ⫾ 0.120 4.7 ⫾ 2.0 28.9 ⫾ 4.3 9.4 ⫾ 0.7 3.9 ⫾ 0.6 4.3 ⫾ 0.4 221 ⫾ 61 35.9 ⫾ 8.4 0.89 ⫾ 0.18 52 ⫾ 40 448 ⫾ 178 20.0 ⫾ 5.2
49–63 0.5–10.0 3.8–64.0 0.700–1.348 0.645–1.220 1–9 20.7–37.6 7.8–11.3 2.8–5.3 3.0–5.1 112–374 18–55 0.5–1.4 10–152 103–760 8–30
Frequency distribution was not normal.
throughout the year in Tehran. According to data from the Iranian Meteorological Organization, annual bright sunshine is 2900 ⫾ 180 h. However, the extent of solar-ultraviolet (UV) exposure is determined primarily by lifestyle rather than outdoor UV irradiance, and most postmenopausal women tend to avoid direct sunlight. Moreover, there are other factors that may contribute to the evident vitamin D deficiency observed in this study. The type of clothing (Islamic garb) used outdoors may contribute to lower exposure to sunlight. The Islamic garb of women in Iran consists of a large black covering, in addition to normal clothes, which covers entire body except the face and hands. Riad El-Sonbaty et al.12 reported a similar finding in veiled Kuwaiti women. Furthermore, air pollution in Tehran, which includes notably high levels of suspended particulate matters, may be another prevention factor, and which may reduce exposure to solar UV rays.4 It should be noted that this preliminary study was the first to determine vitamin D status among Iranians. Therefore, further studies are required to clarify the importance of these and other factors regarding vitamin D status in this subgroup, as well as in other subgroups of the Iranian population. It is also acknowledged that there may have been sampling bias because participants were selected for this study and the sample may not have been representative of the in general population. A weak but significant correlation was found between serum 25-OHD3 and spine BMD in this study; however, the correlation with hip BMD was not significant. This finding suggests that subclinical vitamin D deficiency may contribute to postmenopausal bone loss in which spine bone loss is much more pronounced than that of the hip.6,9,10 The data are in accordance with the findings of Martinez et al.10 and also those of Villareal et al.17 from the midwestern USA, who reported subnormal levels of serum 25-OHD in 49 postmenopausal women (ages 52–77 years) with low vertebral bone mass. Similar to previous reports on seasonal variations of serum 25-OHD levels,7,13,15,16 higher levels of 25-OHD3 were observed during spring than during winter, but the difference was not significant. This may be due to the following factors: (1) the number of samples collected in winter was less than in spring; and (2) sunlight is abundant in Tehran, even in the winter
430
A. Rassouli et al. Vitamin D and BMD in Iranian women
months, so there is no significant change in sunlight exposure in different seasons. Similarly, Tsai et al.16 reported only a small variation of serum 25-OHD levels among urban-dwelling women in Taipei, Taiwan. Conclusion Vitamin D deficiency was shown to be evident as a public health concern in early postmenopausal Iranian women. Serum 25-OHD3 was weakly correlated with spine BMD, which may have physiological significance. More studies are required to clarify vitamin D status in this group as well as in other subgroups of the Iranian population. As vitamin D deficiency is preventable, more public knowledge should be provided to ensure adequate Vitamin D supply. Acknowledgments: The authors thank Dr. M. Mahmoudian, Dr. S. A. Ebrahimi, Dr. A. Kazemi, and E. Jamali for their contributions. We also thank Akbarieh Co. for the gift of 25-OHD3. This work was supported by a grant from the Iran University of Medical Sciences.
References 1. Aksnes, L. A simplified high performance liquid chromatographic method for determination of vitam D3, 25(OH)D2 and 25(OH)D3 in human serum. Scand J. Clin Lab Invest 52:177–182; 1992. 2. Dawson-Huges, B., Dallal, G. E., Krall, E. A., Harris, S., Sokoll, L. J., and Falconer, G. Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women. Ann Int. Med 115:505–511; 1991. 3 Eastell, R. and Riggs, B. L. Vitamin D and osteophorosis. In: Feldman, D., Glorieux, F. H., and Pike, J. W., Eds. Vitamin D, San diego, CA: Academic; 1997; 695–711. 4. Ettinger, R. A. and DeLuca, H. F. The vitamin D endocrine system and is therapeutic potential. Adv Drug Res 28:269 –312; 1996. 5. Hollis, B. W. Assessment of vitamin D mutritional and hormonal status: What to measure and how to do it. Calcif Tissue Int 58:4 –5; 1996. 6. Khaw, K. T., Sneyd, M. J., and Compston, J. Bone density, parathyroid hormone and 25-hydroxyvitamin D concentrations in middle-aged women Br Med J 305:273–277; 1992.
Bone Vol. 29, No. 5 November 2001:428 – 430 7. Landin-Wilhelmsen, K., Wilhelmsen, L., Wilske, J., Lappas, G., Rosen, T., Lindstedt, G., Lundberg, P. A., and Bengtsson, B. A. Sunlight increases serum 25(OH) vitamin D concentration whereas 1,25(OH)2D3 is unaffected. Results from a general population study in Goteborg, Sweden (WHO MONICA Project). Eur J Clin Nutr 49: 400 – 407; 1995. 8. Leboff, M. S., Kohlmeier, L., Hurwitz, S., Franklin, J., Wright, J., and Glowacki J. Occult vitamin D deficiency in postmenopausal US women with hip fracture. JAMA 281:1505–1511; 1999. 9. Lindsay, R. and Meunier, P. J. Osteoporosis: Review of the evidence for prevention, diagnosis and treatment and cost-effectiveness analysis. Osteopor Int 8(Suppl. 4):3–10; 1998. 10. Martinez, M. E., Campo, M. T., Sanchez-Cabezudo, M. J., Garcia, J. A., Sanchez-Calvin, M. T., Torrijos, A., Coya, J., and Munuera, L. Relations between calcidiol serum level and bone mineral density in postmenopausal women with low bone density. Calcif Tissue Int 55:253–256; 1994. 11. Report of a WHO Study Group. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis. WHO Technical Rep Ser 843: 56 –59; 1994. 12. Riad El-Sonbaty, M., and Abdul-Ghaffar, N. U. Vitamin D difficiency in veiled Kuwaiti women. Eur J Clin Nutr 50:315–318; 1996. 13. Scharla, S. H., Scheidt-Nave, C., Leidig, G., Woitge, H., Wuster, C., Seibel, M. J., and Ziegler, R. Lower serum 25OHD is associated with increased bone resorption markers and lower bone density at the proximal femur in normal females: A population-based study. Exp Clin Endocrinol Diabetes 104:289 – 292; 1996. 14. Schmidt-Gayk, H., Bouillon, R., and Roth, H. J. Measurement of vitamin D and its metabolites (calcidiol and calcitriol) and their clinical significance. Scand J Clin Invest 57(Suppl. 227):35– 45; 1997. 15. Sherman, S. S., Hollis, B. W., and Tobin, J. D. Vitamin D status and related parameters in a healthy population: the effect of age, sex and season. J Clin Endocrinol Metab 71:405– 413; 1990. 16. Tsai, K. S., Hsu, S. H., Cheng, J. P., and Yang, R. S. Vitamin D stores of urban women in Taipei: Effect on bone density and bone turnover, and seasonal variation. Bone 20:371–374; 1997. 17. Villareal, D. T., Civitelli, R., Chines, A., and Avioli, L. V. Subclinical vitamin D deficiency in postmenopausal women with low vertebral bone mass. J Clin Endocrinol Metab 72:628 – 634; 1991.
Date Received: September 1, 2000 Date Revised: May 19, 2001 Date Accepted: May 24, 2001
Determination of Serum 25-Hydroxyvitamin D3 Levels in Early Postmenopausal Iranian Women: Relationship With Bone Mineral Density A. RASSOULI,1 I. MILANIAN,1 and M. MOSLEMI-ZADEH2 1 2
Department of Pharmacology, Iran University of Medical Sciences, Tehran, Iran Department of Rheumatology, Loghman-Hakim Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
postmenopausal women have been controversial,3,6,9,10 we performed this preliminary study to determine vitamin D status in early postmenopausal women living in Tehran and the correlation between 25-OHD3 and BMD in the lumbar spine and hip regions.
Serum levels of 25-hydroxyvitamin D3 (25-OHD3) and bone mineral density (BMD) were determined in 73 selected, early postmenopausal women referred to the Bone Densitometry Center, Loghman-Hakim Hospital, Tehran, Iran. The relationship between them was also assessed. 25-OHD3 levels were measured using high-performance liquid chromatography. BMD was measured with dual-energy X-ray absorptiometry of the lumbar spine and proximal femur regions. 25-OHD3 levels ranged from 3.8 to 64.0 ng/mL (mean ⴞ SD: 17.1 ⴞ 11.3). Twenty-six subjects (36%) were vitamin Ddeficient (<12 ng/mL). In the lumbar spine (L2– 4) BMD measurements, 28 subjects (38%) were normal (T score > ⴚ1), 26 (36%) were osteopenic (T < ⴚ1 to >ⴚ2.5), and 19 (26%) were osteoporotic (T < ⴚ2.5). In the hip (total) BMD measurements, 41 subjects (56.1%) were normal, 31 (42.5%) were osteopenic, and 1 (1.4%) was osteoporotic. There was a significant correlation between spine BMD (Z score) and 25-OHD3 (r ⴝ 0.23, p < 0.05), but the correlation was not significant for hip BMD. It was concluded that vitamin D deficiency was evident in early postmenopausal Iranian women, and serum 25-OHD3 was weakly correlated with spine BMD, which may have physiological significance. (Bone 29:428 – 430; 2001) © 2001 by Elsevier Science Inc. All rights reserved.
Materials and Methods Subjects The group studied included 73 early postmenopausal women. They had been selected from a group of 507 early postmenopausal women (within 10 years since menopause) referred to the outpatient Bone Densitometry Center (Loghman-Hakim Hospital, Tehran, Iran) during February to June 2000. All subjects were referred to this center for osteoporosis risk factors, including menopause. Study inclusion criteria were: (1) early postmenopausal status (i.e., 6 months to 10 years since menopause); and (2) residence in Tehran for ⱖ5 years. Exclusion criteria included having a history of: (1) taking drugs known to influence bone metabolism in the past 5 years, such as vitamin D, calcium, corticosteroids, and hormone replacement therapy; (2) musclo skeletal, thyroid, parathyroid, adrenal, hepatic, or renal disease; (3) malignancy; (4) fracture; and (5) hysterectomy. At the time of BMD measurements, the height and weight of the subjects were measured. Moreover, inquiries were made with regard to parity and dietary habits (food frequency).
Key Words: Vitamin D; Bone mineral density (BMD); Menopause; Iran and osteoporosis. Introduction
BMD Measurements
Osteoporosis is an important public health concern, particularly in postmenopausal women.4,9,11 It can be assessed indirectly through a noninvasive measurement of bone mineral density (BMD).9,11 Nevertheless, subclinical vitamin D deficiency, although not sufficient to cause osteomalacia, may lead to secondary hyperparathyroidism and bone loss.8,13 The serum level of 25-dihydroxyvitamin D3 (25-OHD) has been accepted as an index for vitamin D status.1,2,5,14 Because there have been no reports on vitamin D status among the Iranian population, and the data on the relationship between vitamin D status and BMD in
BMD of the lumbar spine (L2– 4, anteroposterior view) and hip (left proximal femur, total) were measured by dual-energy X-ray absorptiometry with a Lunar DPX densitometer. Both T and Z scores were obtained. In the T-score calculations, the manufacturer’s ranges for a USA reference population were used. For Z-score calculations, the manufacturer’s reference data were used for age, weight, and ethnic origin (Asian) adjustments of BMD. Blood Collection and Storage Nonfasting blood samples were collected for biochemical tests at the time of BMD measurements. The sera of the blood samples were separated, divided in small portions, and frozen at ⫺20°C. The sera were analyzed within 2– 4 weeks after sampling.
Address for correspondence and reprints: Dr. Iraj Milanian, Department of Pharmacology, Iran University of Medical Sciences, P.O. Box 141556183, Tehran, Iran. E-mail: [email protected]. © 2001 by Elsevier Science Inc. All rights reserved.
428
8756-3282/01/$20.00 S8756-3282(01)00591-9
Bone Vol. 29, No. 5 November 2001:428 – 430
Biochemical Tests Serum calcium (Ca), phosphorus (P), creatinine (Cr), urea, albumin (Alb), and alkaline phosphatase (ALP) were measured with an RA 1000 autoanalyzer (Technicon). Serum 25-OHD3 levels were measured using a modified high-performance liquid chromatography (HPLC).1 The modification included use of an internal standard (nandrolone decanoate) and changing the mobile phase to methanol:isopropanol:water at 60:28:12. The intraand interassay coefficients of variations were ⬍8% and ⬍10%, respectively. The detection limit was 2.5 ng/mL. Dietary Data Analysis Average daily dietary intakes of vitamin D, calcium, phosphorus, and fiber for the subjects were determined with the assistance of a trained dietitian. Data were obtained using a technique that scores only foods containing considerable levels of these compounds, as determined by nutritional information from the USDA and Canadian NF. Statistical Analysis All data were expressed as mean ⫾ SD. Partial correlation coefficients of variables controlling for age were used to determine the association between variables. For evaluation of the relationship between BMD and other variables, except for age, Z score was used. Means were compared by Student’s t-test. Statistical analyses were performed using SPSS for WINDOWS, release 9.0 (SPSS, Inc.). All probability values were based on two-tailed tests, and p ⬍ 0.05 was considered significant. Whenever data departed substantially from a normal distribution, data transformations were made. Results Distribution characteristics of age, time since menopause, serum 25-OHD3 spine and hip BMD, parity, body mass index (BMI), daily dietary intakes (vitamin D, calcium, phosphorus, and fiber), as well as certain measured serum parameters are summarized in Table 1. Twenty-six subjects (36%) had 25-OHD3 levels of ⬍12 ng/mL. For lumbar spine BMD measurements (T score), 28 subjects (38%) were normal, 26 (36%) were osteopenic, and 19 (26%) were osteoporotic. For hip BMD measurements (T score), 41 subjects (56.1%) were normal, 31 (42.5%) were osteopenic, and 1 (1.4%) was osteoporotic. There was no significant difference between serum 25-OHD3 levels collected in winter (13.3 ⫾ 5.0 ng/mL, n ⫽ 17) and spring (18.3 ⫾ 12 ng/mL, n ⫽ 56). There was a significant correlation between spine BMD (Z score) and 25-OHD3 (r ⫽ 0.23), but for hip BMD the correlation was not significant. There were also no significant correlations between age and 25-OHD3 as well as spine and hip BMD. Time since menopause had a significant correlation only with spine BMD (r ⫽ ⫺0.38). Serum ALP had significant correlations with 25-OHD3 (r ⫽ ⫺0.27), spine BMD (r ⫽ ⫺0.28), and hip BMD (r ⫽ ⫺0.25). Parity has a significant correlation only with spine BMD (r ⫽ ⫺0.24). Other measured serum and dietary parameters had no significant correlations with 25-OHD3 or spine and hip BMD. Discussion The most important finding of this study is that 26 subjects (36%) were vitamin D-deficient. These subjects had 25-OHD3 levels of ⬍12 ng/mL (30 nmol/L), despite ample sunshine
A. Rassouli et al. Vitamin D and BMD in Iranian women
429
Table 1. Distribution characteristics of age, time since menopause (TSM), serum 25-hydroxyvitamin D3 (25-OHD3), spine and hip bone mineral density (BMD), parity, body mass index (BMI), serum calcium (Ca), phosphorus (P), Albumin (Alb), alkaline phosphatase (ALP), urea, and creatinine (Cr), and daily dietary intakes of vitamin D, Ca, and fiber in 73 early postmenopausal Iranian women Variable Age (years) TSM (year) 25-OHD3 (ng/mL)a Spine BMD (g/cm2) Hip BMD (g/cm2) Parity (n) BMI (kg/m2) Ca (mg/dL) P (mg/dL) Alb (g/dL)a ALP (U/L)a Urea (mg/dL) Cr (mg/dL) Vitamin D intake (IU)a Ca intake (mg) Fiber intake (g) a
Mean ⫾ SD
Range
55.7 ⫾ 3.6 4.9 ⫾ 3.1 17.1 ⫾ 11.3 1.018 ⫾ 0.143 0.917 ⫾ 0.120 4.7 ⫾ 2.0 28.9 ⫾ 4.3 9.4 ⫾ 0.7 3.9 ⫾ 0.6 4.3 ⫾ 0.4 221 ⫾ 61 35.9 ⫾ 8.4 0.89 ⫾ 0.18 52 ⫾ 40 448 ⫾ 178 20.0 ⫾ 5.2
49–63 0.5–10.0 3.8–64.0 0.700–1.348 0.645–1.220 1–9 20.7–37.6 7.8–11.3 2.8–5.3 3.0–5.1 112–374 18–55 0.5–1.4 10–152 103–760 8–30
Frequency distribution was not normal.
throughout the year in Tehran. According to data from the Iranian Meteorological Organization, annual bright sunshine is 2900 ⫾ 180 h. However, the extent of solar-ultraviolet (UV) exposure is determined primarily by lifestyle rather than outdoor UV irradiance, and most postmenopausal women tend to avoid direct sunlight. Moreover, there are other factors that may contribute to the evident vitamin D deficiency observed in this study. The type of clothing (Islamic garb) used outdoors may contribute to lower exposure to sunlight. The Islamic garb of women in Iran consists of a large black covering, in addition to normal clothes, which covers entire body except the face and hands. Riad El-Sonbaty et al.12 reported a similar finding in veiled Kuwaiti women. Furthermore, air pollution in Tehran, which includes notably high levels of suspended particulate matters, may be another prevention factor, and which may reduce exposure to solar UV rays.4 It should be noted that this preliminary study was the first to determine vitamin D status among Iranians. Therefore, further studies are required to clarify the importance of these and other factors regarding vitamin D status in this subgroup, as well as in other subgroups of the Iranian population. It is also acknowledged that there may have been sampling bias because participants were selected for this study and the sample may not have been representative of the in general population. A weak but significant correlation was found between serum 25-OHD3 and spine BMD in this study; however, the correlation with hip BMD was not significant. This finding suggests that subclinical vitamin D deficiency may contribute to postmenopausal bone loss in which spine bone loss is much more pronounced than that of the hip.6,9,10 The data are in accordance with the findings of Martinez et al.10 and also those of Villareal et al.17 from the midwestern USA, who reported subnormal levels of serum 25-OHD in 49 postmenopausal women (ages 52–77 years) with low vertebral bone mass. Similar to previous reports on seasonal variations of serum 25-OHD levels,7,13,15,16 higher levels of 25-OHD3 were observed during spring than during winter, but the difference was not significant. This may be due to the following factors: (1) the number of samples collected in winter was less than in spring; and (2) sunlight is abundant in Tehran, even in the winter
430
A. Rassouli et al. Vitamin D and BMD in Iranian women
months, so there is no significant change in sunlight exposure in different seasons. Similarly, Tsai et al.16 reported only a small variation of serum 25-OHD levels among urban-dwelling women in Taipei, Taiwan. Conclusion Vitamin D deficiency was shown to be evident as a public health concern in early postmenopausal Iranian women. Serum 25-OHD3 was weakly correlated with spine BMD, which may have physiological significance. More studies are required to clarify vitamin D status in this group as well as in other subgroups of the Iranian population. As vitamin D deficiency is preventable, more public knowledge should be provided to ensure adequate Vitamin D supply. Acknowledgments: The authors thank Dr. M. Mahmoudian, Dr. S. A. Ebrahimi, Dr. A. Kazemi, and E. Jamali for their contributions. We also thank Akbarieh Co. for the gift of 25-OHD3. This work was supported by a grant from the Iran University of Medical Sciences.
References 1. Aksnes, L. A simplified high performance liquid chromatographic method for determination of vitam D3, 25(OH)D2 and 25(OH)D3 in human serum. Scand J. Clin Lab Invest 52:177–182; 1992. 2. Dawson-Huges, B., Dallal, G. E., Krall, E. A., Harris, S., Sokoll, L. J., and Falconer, G. Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women. Ann Int. Med 115:505–511; 1991. 3 Eastell, R. and Riggs, B. L. Vitamin D and osteophorosis. In: Feldman, D., Glorieux, F. H., and Pike, J. W., Eds. Vitamin D, San diego, CA: Academic; 1997; 695–711. 4. Ettinger, R. A. and DeLuca, H. F. The vitamin D endocrine system and is therapeutic potential. Adv Drug Res 28:269 –312; 1996. 5. Hollis, B. W. Assessment of vitamin D mutritional and hormonal status: What to measure and how to do it. Calcif Tissue Int 58:4 –5; 1996. 6. Khaw, K. T., Sneyd, M. J., and Compston, J. Bone density, parathyroid hormone and 25-hydroxyvitamin D concentrations in middle-aged women Br Med J 305:273–277; 1992.
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Date Received: September 1, 2000 Date Revised: May 19, 2001 Date Accepted: May 24, 2001