There is scientific evidence to support the role of certain B vitamins in male reproductive health, although the strength of evidence varies among the different B vitamins and the specific reproductive functions considered. For instance, vitamin B12 deficiency has been associated with reduced sperm count, impaired motility, and abnormal sperm morphology in some human and animal studies. Supplementation with vitamin B12 has shown improvements in semen quality in men with fertility issues, though results are not universally consistent across all studies.

Folate (vitamin B9) is another B vitamin with a documented impact on male fertility. Folate is involved in DNA synthesis and repair, which are critical processes during spermatogenesis (the production of sperm). Observational studies have linked low folate levels with increased sperm DNA damage and reduced sperm quality. Some clinical trials indicate that folic acid supplementation, occasionally in combination with zinc, may improve sperm parameters, although meta-analyses report mixed outcomes and call for more robust, large-scale trials.

Other B vitamins, such as B6 and niacin (B3), are involved in general energy metabolism and hormone regulation, but evidence for direct effects on male fertility or reproductive system function is limited. Overall, while there is scientific rationale and some supporting data for the use of B vitamins (notably B12 and folate) in supporting aspects of male reproductive health, the quality and consistency of evidence remain moderate.