Heritability and seasonal variability of vitamin D concentrations in male twins

Background Scrum 25 hydroxyvitamin D [25(OH)D] concentrations can be affected by several environmental and Individual factors It is not clear to what extent genetic influences play a role in determining vitamin D status Thus far studies on the heritability of vitamin D have provided conflicting results Objective We estimated the heritability of vitamin D concentrations and the effect of season on heritability estimates Design We measured serum 25(OH)D concentrations in 510 middle aged male twins (310 monozygotic and 200 dizygotic twins) selected from the Vietnam Era Twin Registry) Generalized estimating equations were used to test the association between 25(OH)D and other study factors Structural equation modeling was used to estimate the heritability of 25(OH)D Results The twins mean (+/- SD) age was 55 +/- 2 8 y The mean (+/- SD) 25(OH)D concentration was 38 4 +/- 23 3 ng/mL with a substantial seasonal variation (a 6 1 ng/mL lower value during the winter than during the summer P = 0 003) Approximately 70% of the variation in 25(OH)D concentrations during the winter was explained by genetic factors However in the summer 25(OH)D concentrations were not heritable During the summer 53% of the variation in 25(OH)D concentrations was due to shared environmental factors and 47% of the variation in 25(OH)D concentrations was due to unique environmental factors Conclusions Scrum 25(OH)D concentrations are highly heritable during the winter season only In the summer environmental conditions (eg sun exposure) prevail over genetic backgrounds in determining serum 25(OH)D concentrations This trial was registered at clinicaltrials gov as NCT00017836 Am J Clin Nutr 2010 92 1393-8