Global vitamin D levels in relation to age, gender, skin pigmentation and latitude: an ecologic meta-regression analysis

We performed a meta-analysis of cross-sectional studies on serum 25(OH) D status globally. Serum 25(OH) D levels on average were 54 nmol/l, were higher in women than men, and higher in Caucasians than in non-Caucasians. There was no trend in serum 25(OH) D level with latitude. Vitamin D deficiency was widespread. Introduction We studied vitamin D status (expressed as serum 25-hydroxy-vitamin D [25(OH) D]) in native subjects worldwide. Methods Meta-analysis and meta-regression of studies reporting on 25(OH) D in healthy subjects retrieved from Pubmed, Embase and Web of Science using the terms "serum", "25-hydroxy-vitaminD", "cholecalciferol", and "human". A total of 394 studies were included. Results The mean 25(OH) D level was 54 nmol/l (95% CI: 52-57 nmol/l). Women had borderline significantly higher 25(OH) D levels than men, and Caucasians had higher levels than non-Caucasians. 25(OH) D levels were higher in subjects aged >15 years than in younger subjects. Unadjusted there was no significant decrease in 25(OH) D with latitude (slope of curve-0.03+/-0.12 nmol/l per degree latitude north or south of equator, p=0.8). There was a significant decline with latitude for Caucasians (-0.69+/-0.30 nmol/l per degree, p=0.02), but not for non-Caucasians (0.03+/-0.39 nmol/l per degree, p=0.14). After adjustment for age, gender, and ethnicity, no overall correlation was present between 25(OH) D and latitude (-0.29+/-0.24 nmol/l per degree, p=0.23). Conclusion There was no overall influence of latitude on 25 (OH) D. However, in separate analyses 25(OH) D decreased with latitude in Caucasians but not in non-Caucasians. A widespread global vitamin D insufficiency was present compared with proposed threshold levels.