Key Findings
This meta-analysis assessed the effect of dietary ALA on prostate cancer risk and included 12 observational studies (7 case control and 5 prospective). No significant association between ALA intake and risk of prostate cancer was found. A subgroup analysis of case–control studies found a positive non significant association, but with a lot of variability. The authors note that problems with studies examining ALA include variation in ALA consumption and sources, and population dietary patterns; variation in ALA exposure levels; variation in FFQs and food databases; and variation in adjustment factors and “static” from other PUFAs. Also ALA may be a marker for higher meat and fat intake which increases prostate cancer risk and may be associated with a less than positive dietary pattern and lifestyle.
ABSTRACT
Alpha linolenic acid (ALA) is considered to be a cardioprotective nutrient; however, some epidemiological studies have suggested that dietary ALA intake increases the risk of prostate cancer. The main objective was to conduct a systematic review and meta-analysis of case control and prospective studies investigating the association between dietary ALA intake and prostate cancer risk. Design: A systematic review and meta-analysis were conducted by searching MEDLINE and EMBASE for relevant prospective and case control studies. Included studies: We included all prospective cohort, case control, nested case-cohort and nested case control studies that investigated the effect of dietary ALA intake on the incidence (or diagnosis) of prostate cancer and provided relative risk (RR), HR or OR estimates. Primary outcome measure: Data were pooled using the generic inverse variance method with a random effects model from studies that compared the highest ALA quantile with the lowest ALA quantile. Risk estimates were expressed as RR with 95 per cent CIs. Heterogeneity was assessed by χ2 and quantified by I2. Results: Data from five prospective and seven case control studies were pooled. The overall RR estimate showed ALA intake to be positively but non- significantly associated with prostate cancer risk but the interpretation was complicated by evidence of heterogeneity not explained by study design. A weak, non-significant protective effect of ALA intake on prostate cancer risk in the prospective studies became significant without evidence of heterogeneity on removal of one study during sensitivity analyses. Conclusions: This analysis failed to confirm an association between dietary ALA intake and prostate cancer risk. Larger and longer observational and interventional studies are needed to define the role of ALA and prostate cancer. (Authors abstract)
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