Looks like taking folic acid, which is not natural anyway, can cause/stimulate prostate cancer:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2657096/
"Among the 643 men who were randomly assigned to placebo or supplementation with folic acid, the estimated probability of being diagnosed with prostate cancer over a 10-year period was 9.7% (95% confidence interval [CI] = 6.5% to 14.5%) in the folic acid group and 3.3% (95% CI = 1.7% to 6.4%) in the placebo group
(age-adjusted hazard ratio = 2.63, 95% CI = 1.23 to 5.65, Wald test P = .01). In contrast, baseline dietary folate intake and plasma folate in nonmultivitamin users were inversely associated with risk of prostate cancer,
although these associations did not attain statistical significance in adjusted analyses. These findings highlight the potential complex role of folate in prostate cancer and the possibly different effects of folic acid–containing supplements vs natural sources of folate."