Determinants of Vitamin D in Indian Populations: Understanding the Interplay of Skin Pigmentation, Sun Exposure, and...

The present study evaluates the effects and interaction of skin pigmentation, sun exposure, and genetics on 25(OH)D₃ levels among ostensibly healthy Indians.

Vitamin D₃ was estimated (N = 427) and means were compared between the sexes and study populations. Vitamin D₃ was correlated with Melanin Index (MI) and Weekly Sun Exposure Scores (WSES) using Kendall's tau-b (τb). The effect of age, sex, MI, WSES, and 12 SNPs from vitamin D and skin pigmentation genes were tested on 25(OH)D₃ levels using univariate and multivariate linear models.

A total of 76.6% of the sample were deficient, with males being more deficient than females (p = 0.0016). Deshastha Brahmin caste with lowest MI (42.91 ± 4.47) and WSES (14.4 ± 8.55) reported highest 25(OH)D₃ levels (26.09 ng/mL±16.84). Tribals with higher MI (52.83 ± 7.84-58.83 ± 6.37) and WSES (21.96 ± 7.85-28 ± 0) report low 25(OH)D₃ levels (13.31 ± 7.05-17.94 ± 972). Vitamin D₃ was weakly correlated with MI in Bhils and Kokanas (p < 0.05) and was not significantly correlated with WSES. Multivariate regression shows only sex (p = 0.031), MI (p = 0.018), and WSES (p < 0.001) to be significant predictors of vitamin D levels as compared to age, population, and rs1426654 genotype.

Vitamin D levels vary significantly among populations with widespread deficiency seen in tribal and rural populations, suggesting population-specific environments and behavioral factors to be at play. Targeted dietary fortification is needed, and additional large-scale longitudinal and genome-wide association studies will help identify key factors responsible for vitamin D deficiency among Indian populations.