Journal Name:
Prostaglandins Leukot. Essent. Fatty Acids
Article Title:
Omega-3 PUFA: Good or bad for prostate cancer?
Date Written:
2008
Volume:
79
Number:
3
Page:
97
Author(s):
Brouwer, I.A.
Article:
Prostate cancer is the second most common cancer in men in the World. Dietary factors have been associated with the occurrence of prostate cancer.There are some indications that alpha-linolenic acid (ALA) and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may differently affect the risk of prostate cancer. This review provides an overview of human studies on the relationship of the omega 3 fatty acids with the risk of prostate cancer. The objective of this meta-analysis was to estimate quantitatively the associations between intake or status of omega-3 PUFA fatty acids and occurrence of prostate cancer in observational studies in humans. Risk estimates across studies were combine using random-effects models. Thirteen observational studies that investigated the relationship between intake of ALA or blood levels of ALA and prostate cancer incidence or prevalence were assessed. Blood levels of ALA reflect intake of ALA. Of these 13 studies 7 were prospective studies and 6 were case-control studies. The combined estimates showed an increased risk of prostate cancer in men with a high intake or blood level of ALA (combined relative risk (RR) 1.36; 95% CI 1.08-1.70). The association is stronger in the case-control studies (RR 1.84; 95% CI 1.04-3.25) than in the prospective studies (RR 1.10; 0.91-1.32). Eight observational studies on EPA intake or blood concentrations and prostate cancer were studied of which 5 were prospective and 3 were case-control studies. Seven observational studies on DHA intake or blood concentration; of which 4 were prospective studies and 3 were case-control studies. EPA and DHA were not significantly associated with prostate cancer.
The association between high intake of ALA and prostate cancer needs further study especially basis the fact that the prospective studies do not show a clear association. This makes a true effect of intake of ALA on prostate cancer less likely. Also most studies did not differentiate between dietary sources of ALA making direct correlations more difficult to support. The author notes that when interpreting the results, there was considerable heterogeneity among the studies. For example, the overall estimate of 1.36 for ALA takes both case control and prospective studies into account. In the case-control studies, information on intake and or blood samples has been collected after the development of the disease. It is possible that the disease has influenced the intake or status of the patients and thereby obscured the association. In the prospective studies, information on intake or blood samples has been collected before the occurrence of the disease. Therefore, prospective studies are generally considered to have a stronger study design. Thus, the results of the prospective studies deserve more emphasis than the results of the case-control studies. Other explanations for heterogeneity can include differences in the background diet of the populations, random error and publication bias.
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