All:
I've long emphasized the evidence that ALA is at least as good, if not better, for cardiovascular disease and total mortality as long-chain omega-3 (fish oil/EPA/DHA). The return worry is always the studies linking ALA intake to risk of prostate cancer. I've long held that these data are highly confounded and quite likely artifactual, and in any case noted that total mortality trumps individual disease risk even if the association is real. (See here and here, including the embedded links in the latter post leading here and here).
The evidence from two recent meta-analyses suggests that there is in fact no convincing association for ALA intake and prostate cancer. One analysis suggests that there may even be a teensy-tinsy decrease in risk above a 1.5 g/d threshold.
Cancer Causes Control. 2010 Mar;21(3):347-55.
Prospective studies of dietary alpha-linolenic acid intake and prostate cancer risk: a meta-analysis.
Carayol M, Grosclaude P, Delpierre C.
Individual-based studies that investigated the relation between dietary alpha-linolenic acid (ALA) intake and prostate cancer risk have shown inconsistent results. We carried out a meta-analysis of prospective studies to examine this association. [...] Comparing the highest to the lowest ALA intake category, the pooled RR was 0.97 (95% CI:0.86-1.10) but the association was heterogeneous. Using the reported numbers of cases and non-cases in each category of ALA intake, we found that subjects who consumed more than 1.5 g/day of ALA compared with subjects who consumed less than 1.5 g/day had a significant decreased risk of prostate cancer: RR = 0.95 (95% CI:0.91-0.99). Divergences in results could partly be explained by differences in sample sizes and adjustment but they also highlight limits in dietary ALA assessment in such prospective studies. Our findings support a weak protective association between dietary ALA intake and prostate cancer risk but further research is needed to conclude on this question.
PMID: 19921446 [PubMed - indexed for MEDLINE]
Am J Clin Nutr. 2009 May;89(5):1558S-1564S. Epub 2009 Mar 25.
The relation of alpha-linolenic acid to the risk of prostate cancer: a systematic review and meta-analysis.
Simon JA, Chen YH, Bent S.
BACKGROUND: alpha-Linolenic acid (ALA; 18:3n-3) has been associated inconsistently with an increased risk of prostate cancer. Additional studies have become available since the publication of 2 previous meta-analyses. [...] The relation between ALA and prostate cancer is inconsistent across studies. We pooled data from 8 case-control and 8 prospective studies. The summary estimate revealed that high ALA dietary intakes or tissue concentrations are weakly associated with prostate cancer risk (relative risk [RR]: 1.20; 95% CI: 1.01, 1.43). When examined by study type (ie, retrospective compared with prospective or dietary ALA compared with tissue concentration) or by decade of publication, only the 6 studies examining blood or tissue ALA concentrations revealed a statistically significant association. With the exception of these studies, there was significant heterogeneity and evidence of publication bias. After adjustment for publication bias, there was no association between ALA and prostate cancer (RR: 0.96; 95% CI: 0.79, 1.17). CONCLUSIONS: Studies examining the relation between ALA and prostate cancer have produced inconsistent findings. High ALA intakes or high blood and adipose tissue concentrations of ALA may be associated with a small increased risk of prostate cancer. However, these conclusions are qualified because of the heterogeneity across studies and the likelihood of publication bias.
PMID: 19321563 [PubMed - indexed for MEDLINE]
Note that much of the association with ALA tissue levels came from case-control studies, which are an inherently weaker study design than prospective studies; also, the accumulation of ALA in tissues may be due to reasons other than intake of ALA, such as defective desaturation or idiosyncratic deposition.
