Abstract
BackgroundAlthough environmental factors, mainly nutrition and UV-B radiation, have been considered major determinants of vitamin D status, they have only explained a modest proportion of the variation in serum 25-hydroxyvitamin D. We aimed to study the seasonal impact of genetic factors on serum 25-hydroxyvitamin D concentrations.Methodology/Principal findings204 same-sex twins, aged 39–85 years and living at northern latitude 60°, were recruited from the Swedish Twin Registry. Serum 25-hydroxyvitamin D was analysed by high-pressure liquid chromatography and mass spectrometry. Genetic modelling techniques estimated the relative contributions of genetic, shared and individual-specific environmental factors to the variation in serum vitamin D. The average serum 25-hydroxyvitamin D concentration was 84.8 nmol/l (95% CI 81.0–88.6) but the seasonal variation was substantial, with 24.2 nmol/l (95% CI 16.3–32.2) lower values during the winter as compared to the summer season. Half of the variability in 25-hydroxyvitamin D during the summer season was attributed to genetic factors. In contrast, the winter season variation was largely attributable to shared environmental influences (72%; 95% CI 48–86%), i.e., solar altitude. Individual-specific environmental influences were found to explain one fourth of the variation in serum 25-hydroxyvitamin D independent of season.Conclusions/SignificanceThere exists a moderate genetic impact on serum vitamin D status during the summer season, probably through the skin synthesis of vitamin D. Further studies are warranted to identify the genes impacting on vitamin D status.
Highlights
Vitamin D is unique among vitamins because it can be synthesised endogenously by skin exposure to UV-B radiation
Sufficient levels of 1,25dihydroxyvitamin D have a negative feedback on the secretion of parathyroid hormone [3]. 25-hydroxyvitamin D can be stored in body fat and mobilised when needed and thereby avoiding deficiency during the winter season
During the winter season when UV-B radiation is minimal at latitude 60u north and the cutaneous synthesis of pre-vitamin D is non-existent [26], the heritability was undetectable
Summary
Vitamin D is unique among vitamins because it can be synthesised endogenously by skin exposure to UV-B radiation. Sun exposure is the most important source of vitamin D [1]. Dietary intake by natural food sources, food fortification or dietary supplements is of importance because exposure to UV-B radiation is low during the winter season [2]. The primary step in endogenous vitamin D synthesis is the formation of pre-vitamin D3 from activation of 7-dehydrocholesterol when the skin is exposed to UV-B. Mainly nutrition and UV-B radiation, have been considered major determinants of vitamin D status, they have only explained a modest proportion of the variation in serum 25hydroxyvitamin D. We aimed to study the seasonal impact of genetic factors on serum 25-hydroxyvitamin D concentrations
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