Journal
AMERICAN JOURNAL OF EPIDEMIOLOGY
Volume 174, Issue 12, Pages 1363-1372Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/aje/kwr258
Keywords
alkaline phosphatase; parathyroid hormone; seasons; vitamin D
Categories
Funding
- National Heart, Lung, and Blood Institute [U01 HL080295, R01 HL087652]
- National Institute of Neurological Disorders and Stroke
- National Institutes of Health [R01 HL084443, R01AG027002, R01HL096875, 1KL2RR025015]
- National Center for Research Resources [M01-RR00425]
- National Institute of Diabetes and Digestive and Kidney Diseases [DK063491]
- [N01-HC-85239]
- [N01-HC-85079]
- [N01-HC-85086]
- [N01-HC-35129]
- [N01 HC-15103]
- [N01 HC-55222]
- [N01-HC-75150]
- [N01-HC-45133]
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Low circulating concentrations of 25-hydroxyvitamin D (25(OH)D) are associated with adverse health outcomes in diverse populations. However, 25(OH)D concentrations vary seasonally with varying exposure to sunlight, so single measurements may poorly reflect long-term 25(OH)D exposure. The authors investigated cyclical trends in average serum 25(OH)D concentrations among 2,298 individuals enrolled in the Cardiovascular Health Study of community-based older adults (1992-1993). A sinusoidal model closely approximated observed 25(OH)D concentrations and fit the data significantly better than did a mean model (P < 0.0001). The mean annual 25(OH)D concentration was 25.1 ng/mL (95% confidence interval: 24.7, 25.5), and the mean peak-trough difference was 9.6 ng/mL (95% confidence interval: 8.5, 10.7). Male sex, higher latitude of study site, and greater physical activity levels were associated with larger peak-trough difference in 25(OH)D concentration (each P < 0.05). Serum concentrations of intact parathyroid hormone and bone-specific alkaline phosphatase also varied in a sinusoidal fashion (P < 0.0001), inversely to 25(OH)D. In conclusion, serum 25(OH)D varies in a sinusoidal manner, with large seasonal differences relative to mean concentration and laboratory evidence of biologic sequelae. Single 25(OH)D measurements might not capture overall vitamin D status, and the extent of misclassification could vary by demographic and behavioral factors. Accounting for collection time may reduce bias in research studies and improve decision-making in clinical care.
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