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.