Omega-3 linked to lower colorectal cancer risk
fish may slash the risk of developing colorectal cancer by 40 per
cent, suggests a new study.
Over an impressive 22 years of study, both omega-3 and fish intake were associated with cancer risk reduction in the colon and rectum, according to findings by researchers from Harvard and Columbia University published in the journal Cancer Epidemiology, Biomarkers & Prevention. The research adds to the healthy reputation of omega-3 fatty acids that is seeping into consumer consciousness, based largely on evidence that it can aid cognitive function, may help protect the heart against cardiovascular disease, and could reduce the risk of certain cancers. In terms of colorectal cancer, a disease response for about 492,000 deaths each year around the world, the potential benefits have only been investigated in a small number of studies. According to a recent meta-analysis by researchers from Wageningen University in the Netherlands, the overall body of science indicates that the incidence of colorectal cancer may be cut by 12 per cent by consuming more fish per week. In addition, for every additional serving of fish consumed per week the risk of developing the cancer could be cut by four per cent, stated the meta-analysis in the American Journal of Epidemiology. In terms of the Harvard-Columbia University study, Megan Hall and co-workers followed 21,376 men participating in the Physicians' Health Study (PHS) trial (started in 1982) for an average of 22 years. The men's intake of fish, and subsequently omega-3 fatty acid intake, was calculated from an abbreviated food-frequency questionnaire. Over the course of the study, 500 cases of colorectal cancer were diagnosed. In terms of fish intake, the highest average intake was associated with a 40 per cent reduction in the risk of colorectal cancer. In addition, this link was relevant for both colon and rectal cancers. When the scientists focussed on omega-3 fatty acid consumption, they found similar associations, with the highest intakes linked to a 26 per cent reduction in colorectal cancer risk, compared to the lowest average intake. "Our results from this long-term prospective study suggest that intakes of fish and long-chain n-3 fatty acids from fish may decrease the risk for colorectal cancer," concluded Hall. Different omega-3, different effects A study published last year in the American Journal of Epidemiology (Vol. 166, pp. 1116-1125) reported that different omega-3 fatty acids conferred different levels of protection. Indeed, increased intake of eicosapentaenoic acid (EPA) was associated with a 41 per cent reduction in risk, while docosahexaenoic acid (DHA) was associated with a 37 per cent reduction in risk, comparing highest against lowest average intakes. It has previously been proposed that omega-3 fatty acids may inhibit the omega-6 arachidonic acid (AA) cascade that has been linked to cancer formation and cell proliferation. Metabolism of fatty acids produces compounds called prostaglandins, which can be either pro- or anti-inflammatory. The prostaglandins derived from omega-3 fatty acids are said to be anti-inflammatory and may protect against the development of cancer, while prostaglandins derived from omega-6 fatty acids, like AA, are proposed to be pro-inflammatory. Physicians' Health Study - bringer of good news The study began life as a randomised trial investigating the effect of beta-carotene supplements and aspirin on cancer and cardiovascular disease. The data has since been expanded to focus on other foods and nutrients and different disease types. Indeed, the long-term beta-carotene supplementation was associated with significantly higher scores in cognitive tests, compared to placebo. On the other hand, men taking part in the study for less than ten years displayed no differences in cognition regardless of whether they took beta-carotene or placebo. The study, published in the Archives of Internal Medicine, was the first to look at long-term antioxidant supplementation in relation to a decline in cognitive function that occurs with naturally with age, and that precedes diseases such as Alzheimer's. On another track, data from the Physicians' Health Study also indicated that the consumption of at least one serving of whole grains cereal, but not refined cereals, a day could reduce a man's risk of heart failure by 30 per cent. This study was also published in the Archives of Internal Medicine. Source: Cancer Epidemiology, Biomarkers & Prevention 1 May 2008, Volume 17, Pages 1136-1143,. doi: 10.1158/1055-9965.EPI-07-2803 "A 22-year Prospective Study of Fish, n-3 Fatty Acid Intake, and Colorectal Cancer Risk in Men" Authors: M.N. Hall, J.E. Chavarro, I.-M. Lee, W.C. Willett, J. Ma