DHA and Prostate Cancer
On April 27, Dr. Neal Barnard of PCRM wrote about a study, the Prostate Cancer Prevention Trial (1), which found that men with a higher percentage of DHA in their blood had a higher risk of high grade prostate cancer (Omega-3 Fatty Acids Linked to Prostate Cancer Risk). Dr. Barnard’s article also suggested that eating fish (the primary source of DHA for most people) five times or more a week could cause type 2 diabetes. People have written me asking if this means they should stop taking DHA supplements.
Based on the results from the Prostate Cancer Prevention Trial (PCPT) and some other studies, it is probably safe to conclude that large amounts of DHA do not prevent prostate cancer, but I think it is too soon to say that large amounts causes it. There are many variables when comparing percentages of fatty acids and disease, and the results tend to be all over the map. For example, the report from PCPT also found that the dreaded trans fats were inversely linked to high grade prostate cancer.
The levels of DHA in the blood of the men who had a higher rate of prostate cancer in the PCPT were >3.3% (compared to the lowest category of ≤2.6%), whereas vegans tend to have much lower levels of DHA, typically about 1% (see Omega-3 Fatty Acid Recommendations for Vegetarians).
DHA (and EPA) are normally promoted for reducing heart disease, but that is only a minor reason why I promote it for vegans. Vegans have much lower levels than omnivores and my concern is getting enough DHA for nerve tissue to function optimally. The amounts I recommend are much lower than what are typically suggested for fish oil supplements (usually 500 mg per day or more). I would not recommend taking that much DHA, EPA, or a combination.
It is still a good idea for vegans to take DHA at the rate of 200 to 300 mg every 2 to 3 days. The recent research does give me some pause in continuing to recommend 200 to 300 mg per day for those over 60 years old, cutting that down to every other day might be prudent. Unfortunately, there is no research showing how much these amounts of DHA will raise blood levels of DHA in vegans, but based on related research, I do not think it is enough to raise it much above 2%, which would still put someone in the lowest category of DHA percentage from the PCPT trial.
1. Brasky TM, Till C, White E, Neuhouser ML, Song X, Goodman P, Thompson IM, King IB, Albanes D, Kristal AR. Serum Phospholipid Fatty Acids and Prostate Cancer Risk: Results From the Prostate Cancer Prevention Trial. Am J Epidemiol. 2011 Apr 24. [Epub ahead of print] (Link)