Vitamin D is important for optimal¹（最佳的） reproductive function in both animals and humans. It has long been known that serum²（血清，浆液） vitamin D level is important for reproductive function in various animals, but now researchers from the University of Copenhagen and Copenhagen University Hospital have shown that this relationship can also be demonstrated in humans. A new study conducted in 300 normal men showed a positive correlation³ between the percentage of motile sperm⁴ and serum vitamin D levels. The study was recently published in the scientific journal Human Reproduction, and showed additionally that stimulation⁵ of human spermatooza in the laboratory with activated⁶ vitamin D can increase their forward movement.

"Our study is not sufficient and should not be used to change existing treatment practices. However, it uncovers some of the functions of vitamin D and generates new hypotheses. This is an intriguing⁷（有趣的） finding, because it suggests that vitamin D has an effect on sperm movement and function," explains Martin Blomberg Jensen from Copenhagen University Hospital.

"However, this finding is not sufficient in determining whether vitamin D supplements may improve sperm quality in normal or infertile⁸ males. This study is one in a line of studies indicating that vitamin D is necessary for male reproduction," says Martin Blomberg Jensen.

Today, there is no known medical treatment proved to improve semen quality in well-designed randomised trials, although several papers have shown numerous positive associations between various drugs such as antioxidants, zinc⁹, various vitamins etc. and semen quality.

"Low semen quality may have numerous causes, but it often has a fetal origin similar to some male genital（生殖器） malformations and testicular（睾丸） cancer. However, this study indicates that factors in adult life may also play a role for semen quality," says Professor Anders Juul from the University of Copenhagen and Copenhagen University Hospital's Department of Growth and Reproduction.

"It is important to find all factors of importance, because semen qaulity in Danish men is at a low level and contributing to a very high incidence of fertility problems among Danish couples," says Anders Juul.

The authors conclude that there is a need to intensify¹⁰ reproductive research to identify relevant factors and conduct placebo-controlled trials to clarify whether vitamin D supplements are beneficial for infertile men.