One study demonstrated that higher serum vitamin D levels were correlated with lower prostate cancer aggression, at a rate of a 9% decrease in mortality per 20 nmol/L increase in 25-hydroxyvitamin D3 concentration [9]. In addition, vitamin D supplements have been shown to reduce PSA concentration and thus likely slow the progression of prostate tumors [15]. The gene discussed is KLK3; the disease is Familial prostate cancer.