B vitamins, particularly B6, B9 (folate), and B12, are essential for general cellular metabolism, hormone synthesis, and DNA replication, which are all processes involved in testicular function. There is scientific evidence that deficiencies in these vitamins can impair spermatogenesis, testosterone production, and overall male fertility. For example, folate and B12 are required for proper DNA synthesis in rapidly dividing spermatogenic cells. Some studies have shown that supplementation with folic acid and B12 may improve sperm count or motility in subfertile men, though results are mixed and often limited by small sample sizes or confounding factors. B6 is involved in steroid hormone metabolism, including testosterone, but direct evidence linking B6 supplementation to improved testicular health in healthy individuals is limited.

It is important to note that while B vitamins are critical for normal testicular and reproductive function, there is little evidence that supplementation above recommended dietary intake provides benefit for testicular health in men who are not deficient. Most clinical guidelines recommend ensuring adequate B vitamin intake through diet rather than supplementation, unless a deficiency exists or is suspected. Thus, the scientific support for B vitamin supplementation specifically for testicular health is modest and primarily relevant in the context of correcting a deficiency.