Objective Studies in rodents indicate a role of vitamin D in male reproduction, but the relationship between vitamin D and androgen levels in men is largely unexplored. We aimed to investigate the association of 25-hydroxyvitamin D [25(OH)D] levels with testosterone, free androgen index (FAI) and SHBG. Moreover, we examined whether androgen levels show a similar seasonal variation to 25(OH)D.
Design In this cross-sectional study, 25(OH)D, testosterone and SHBG levels were assessed by immunoassay in 2299 men who were routinely referred for coronary angiography (1997–2000).
Measurements Main outcome measures were associations of 25(OH)D levels with testosterone, SHBG and FAI. FAI was calculated as testosterone (nmol/l)/SHBG (nmol/l) × 100.
Results Men with sufficient 25(OH)D levels (≥30 μg/l) had significantly higher levels of testosterone and FAI and significantly lower levels of SHBG when compared to 25(OH)D insufficient (20–29·9 μg/l) and 25(OH)D-deficient (<20 μg/l) men (P < 0·05 for all). In linear regression analyses adjusted for possible confounders, we found significant associations of 25(OH)D levels with testosterone, FAI and SHBG levels (P < 0·05 for all). 25(OH)D, testosterone and FAI levels followed a similar seasonal pattern with a nadir in March (12·2 μg/l, 15·9 nmol/l and 40·8, respectively) and peak levels in August (23·4 μg/l, 18·7 nmol/l and 49·7, respectively) (P < 0·05 for all).
Conclusion Androgen levels and 25(OH)D levels are associated in men and reveal a concordant seasonal variation. Randomized controlled trials are warranted to evaluate the effect of vitamin D supplementation on androgen levels.