Re: Are serum levels of vitamin d associated with semen quality? Results from a cross-sectional study in young healthy men.

OBJECTIVE To examine the association between low serum vitamin D concentration and estimates of male reproductive function. DESIGN Cross-sectional study. SETTING University hospital. PATIENT(S) From a Danish pregnancy cohort established in 1984-1987, 347 sons were selected for a study conducted in 2005-2006. INTERVENTION(S) Semen parameters and reproductive hormones were related to vitamin D concentrations in 307 men. MAIN OUTCOME MEASURE(S) Semen characteristics and reproductive hormones. RESULT(S) A high vitamin D level was unexpectedly associated with lower crude median total sperm count and percentage of normal morphology sperm and a high level of crude median sex hormone-binding globulin and FSH. After adjustment, the associations attenuated to nonsignificant associations, except for sex hormone-binding globulin. Additionally, adjusted free androgen index was lower at higher vitamin D levels, and men with high vitamin D had 11% (95% confidence interval, 1%-20%) lower free androgen index compared with men with low vitamin D. CONCLUSION(S) These results do not indicate that low vitamin D is a risk factor for poor semen quality in a population of young healthy men, but we may not have enough men with low vitamin D levels to detect an effect. New studies should include a larger proportion of vitamin D-deficient men.