title: Folate intake, serum folate levels, and prostate cancer risk: a meta-analysis of prospective studies.
abstract: BACKGROUND
  Studies have reported inconsistent results concerning the existence of associations of folate intake and serum folate levels with prostate cancer risk. This study sought to summarise the evidence regarding these relationships using a dose-response meta-analysis approach.
  
  
  METHODS
  In January 2014, we performed electronic searches of PubMed, Embase, and the Cochrane Library to identify studies examining the effect of folate on the incidence of prostate cancer. Only prospective studies that reported effect estimates with 95% confidence intervals (CIs) of the incidence of prostate cancer for more than 2 categories of folate were included.
  
  
  RESULTS
  Overall, we included 10 prospective studies reporting data on 202,517 individuals. High dietary folate intake had little or no effect on prostate cancer risk (risk ratio [RR] = 1.02; 95% CI = 0.95-1.09; P = 0.598). The dose-response meta-analysis suggested that a 100 μg per day increase in dietary folate intake has no significant effect on the risk of prostate cancer (RR = 1.01; 95% CI = 0.99-1.02; P = 0.433). However, high serum folate levels were associated with an increased risk of prostate cancer (RR = 1.21; 95% CI = 1.05-1.39; P = 0.008). The dose-response meta-analysis indicated that a 5 nmol/L increment of serum folate levels was also associated with an increased risk of prostate cancer (RR = 1.04; 95% CI = 1.00-1.07; P = 0.042).
  
  
  CONCLUSIONS
  Our study indicated that dietary folate intake had little or no effect on prostate cancer risk. However, increased serum folate levels have potentially harmful effects on the risk of prostate cancer.
authors.forename: Rong
authors.initials: R
authors.lastname: Wang
authors.forename: Yan
authors.initials: Y
authors.lastname: Zheng
authors.forename: Jing-Yang
authors.initials: JY
authors.lastname: Huang
authors.forename: Ai-Qin
authors.initials: AQ
authors.lastname: Zhang
authors.affiliation: Department of Rehabilitation Institute, Shanghai Seventh People's Hospital, Shanghai, China. zhou_ly@126.com.
authors.forename: Yu-Hao
authors.initials: YH
authors.lastname: Zhou
authors.forename: Jie-Ning
authors.initials: JN
authors.lastname: Wang
mesh_terms: D002277:Carcinoma / Q000097:blood / Q000453:epidemiology*; D004032:Diet / Q000706:statistics & numerical data*; D005492:Folic Acid / Q000097:blood*; D006801:Humans; D015994:Incidence; D008297:Male; D016017:Odds Ratio; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000097:blood / Q000453:epidemiology*; D012306:Risk
chemical_list: D005492:Folic Acid