Abstract
BackgroundStudies 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.MethodsIn 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.ResultsOverall, 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).ConclusionsOur 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.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2458-14-1326) contains supplementary material, which is available to authorized users.
Highlights
Studies have reported inconsistent results concerning the existence of associations of folate intake and serum folate levels with prostate cancer risk
Five prospective cohort studies [8,9,10,11,12] involving a total of 192,702 individuals, between 14,620 and 65,836 men were included in each study, and follow-up periods ranged from 9.0 to 17.3 years evaluated the association between dietary folate intake and the risk of prostate cancer, and the remaining 5 nested case control studies [7,13,14,15,16] investigated the association between serum folate levels and the risk of prostate cancer for a total of 9810 individuals, between 321 and 6000 blood samples were included in each study, and follow-up periods ranged from 4.9 to 15.7 years
After integrating all of the available evidence, we found that increased serum folate levels are associated with an increased risk of prostate cancer; increased dietary folate intake has no significant effect on the risk of prostate cancer
Summary
Studies have reported inconsistent results concerning the existence of associations of folate intake and serum folate levels with prostate cancer risk. Data on the effect of dietary folate intake or serum folate levels on subsequent prostate cancer morbidity are limited and inconclusive. The results of a previous prospective study [7] indicated that dietary folate intake was associated with a greater risk of prostate cancer at a certain dose. Several other prospective studies [8,9,10,11,12,13,14,15,16] revealed that folate intake has little or no effect on the risk of prostate cancer. Traditional case control studies are sensitive to confounding factors and bias, especially recall bias
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