BETHESDA, MARYLAND. Alpha-linolenic acid (ALA) is a major component of flaxseed oil and has been associated with significant cardiovascular benefits. Some studies, however, have shown that a high intake of ALA is associated with an increased risk of prostate cancer. A prestigious team of researchers from the National Cancer Institute, the Harvard Medical School, the Harvard School of Public Health, and the Karolinska Institutet in Stockholm has just released the results of a study aimed at settling the controversy as to whether or not ALA is detrimental when it comes to prostate cancer. The researchers also determined the effect of other fatty acids, including fish oils, on prostate cancer risk.
The study involved 47,866 male American health professionals who were followed over a 14-year period beginning in 1986. The participants completed detailed food frequency questionnaires in 1986, 1990 and 1994. By the year 2000, 2965 new cases of prostate cancer had been reported with 448 of these being advanced (metastasized) or fatal. The overall incidence of new prostate cancer detected over the 14- year period was 0.5% per year.
The researchers found no correlation between ALA intake and overall prostate cancer risk, but did observe a strong association between a high ALA intake and the risk of advanced prostate cancer. Men with a high ALA intake (greater than 0.58% of energy or about 1.3 grams/day) were twice as likely to develop advanced prostate cancer as were men with a lower intake (less than 0.37% of energy or about 0.8 grams/day) even after adjusting for all other known variables that could affect the risk. The risk was slightly higher for ALA from non-animal sources than for ALA from meat and dairy sources. There was a trend for red meat, mayonnaise and salad dressings to be associated with a higher risk. The intake of two other abundant fatty acids, linoleic acid and arachidonic acid, was not related to prostate cancer risk.
The team of researchers found a protective effect associated with a high intake of fish oils - eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Men with a daily intake of more than 0.214% of daily energy (about 470 mg/day) were 11% less likely to develop prostate cancer than were men with an intake less than 0.057% of energy (about 125 mg/day). The beneficial effect of EPA plus DHA was particularly pronounced in regard to the incidence of advanced prostate cancer. Fish oil supplements were slightly less effective than fish oils from fatty fish perhaps indicating that vitamin D and vitamin A are necessary to obtain the maximum benefit.
Leitzmann, MF, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. American Journal of Clinical Nutrition, Vol. 80, July 2004, pp. 204-16