The Eurasian lactase persistence variant LCT-13910 C/T is associated with vitamin D levels in individuals living at high latitude, more so than exposure to sunlight.

Rapid selection of a genetic variant that confers continuous life-long lactase production in Europeans (LCT-13910 C/T) has been attributed to the advantages of acquiring nutrients from consuming milk without the disadvantages of lactose malabsorption. Individuals with this genetic lactase persistence (LP) variant generally consume more milk and have been shown to have higher levels of serum vitamin D. Vitamin D is the principal regulator of Ca absorption and its synthesis in skin is dependent on UVB exposure. The primary aim of the present study was to compare serum vitamin D concentrations with LP variant and to control for UVB exposure. Data from over 100 000 individuals living in Norway, a country with low UVB exposure, was retrospectively retrieved for comparison of genetic LP variant, serum 25-hydroxyvitamin D (25(OH)D) concentration and the time of year when serum samples were taken. For comparison, a similar analysis was performed with a natural dairy micronutrient, namely vitamin B12. It was found that individuals with the genetic LP variant had considerably higher levels of serum 25(OH)D (P < 2 × 10-16, Cohen's d = 0·73) but lower levels of vitamin B12 (P < 2 × 10-16, Cohen's d = 0·11), compared with genetic lactase non-persistent individuals, even when controlled for seasonality, age and sex. The difference in serum 25(OH)D levels did not diminish in summer months, showing the role of vitamin D in LP variant selection in areas of low UVB irradiation. LP variant selection advantage through acquiring another dairy micronutrient, vitamin B12, was not observed.