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

ObjectiveTo examine the association between low serum vitamin D concentration and estimates of male reproductive function.DesignCross-sectional study.SettingUniversity 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.