Background/objectives The prevalence of vitamin D deficiency among seniors is high. Whereas sun exposure, vitamin D intake, genes, demographics, and lifestyle have been identified as being important determinants of vitamin D status, the impact of these factors is expected to differ across populations. To improve current prevention and treatment strategies, this study aimed to explore the main determinants of vitamin D status and its relative importance in a population of community-dwelling Dutch older adults. Methods/subjects Serum 25-hydroxyvitamin D (25(OH)D) was measured in 2857 adults aged ≥65 years. Sun exposure was assessed with a structured questionnaire (n = 1012), vitamin D intake using a Food Frequency Questionnaire (n = 596), and data on genetic variation that may affect 25(OH)D status was obtained for 4 genes, DHCR7 (rs12785878), CYP2R1 (rs10741657), GC (rs2282679), and CYP24A1 (rs6013897) (n = 2530). Results Serum 25(OH)D concentrations <50 nmol/L were observed in 45% of the population; only 6% of these participants used vitamin D supplements. Sun exposure (being outside daily during summer: 66 ± 25 nmol/L vs not being outside daily during summer: 58 ± 27 nmol/L, P = 0.02) and vitamin D intake (per unit μg/day during winter/spring: 3.1 ± 0.75 nmol/L, P < 0.0001) were associated with higher 25(OH)D concentrations. Major allele carriers of SNPs related to DHCR7, CYP24A1, and GC, as well as CYP2R1 minor allele carriers had the highest 25(OH)D concentrations. Together, sun (R2 = 0.29), vitamin D intake (R2 = 0.24), and genes (R2 = 0.28) explained 35% (R2 = 0.35) of the variation in 25(OH)D concentrations during summer/autumn period, when adjusted for age, sex, BMI, education, alcohol consumption, smoking, physical activity, and self-rated health status (n = 185). Conclusion The investigated determinants explained 35% of 25(OH)D status. Of the three main determinants under study, sun exposure still appeared to be an important determinant of serum 25(OH)D in older individuals, closely followed by genes, and vitamin D intake. Given the low frequency of vitamin D supplement use in this population, promoting supplement use may be an inexpensive, easy, and effective strategy to fight vitamin D deficiency.

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The Journal of Steroid Biochemistry and Molecular Biology
Department of Internal Medicine

Brouwer-Brolsma, E., Vaes, A.M.M. (Anouk M.M.), van der Zwaluw, N., van Wijngaarden, J., Swart, K., Ham, A., … de Groot, L. (2016). Relative importance of summer sun exposure, vitamin D intake, and genes to vitamin D status in Dutch older adults: The B-PROOF study. The Journal of Steroid Biochemistry and Molecular Biology (Vol. 164, pp. 168–176). doi:10.1016/j.jsbmb.2015.08.008