More than 30 years ago scientists first noted a significantly reduced risk of cardiovascular disease (CVD) in Greenland Eskimos, whose diet consists predominantly of fish and seal—both rich sources of polyunsaturated fatty acids. Subsequent research identified that the cardioprotective effect of fish was due primarily to two long-chain omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Research conducted over the past three decades continues to strongly support the role of omega-3 fatty acids in heart health and, most recently, in reducing the risk of colon cancer.
No Fish Tale for the Heart
Cardiovascular disease remains the leading cause of death in the United States, killing someone every 35 seconds. The good news is that a number of readily available functional foods can reduce the risk of heart disease. Without question, fish and other foods rich in omega-3 fatty acids are among the most effective.
The Harvard Center for Risk Analysis recently convened an expert panel to quantify the impact of fish consumption on coronary heart disease (CHD) risk. The panel found that, compared to consuming no fish, eating small quantities of fish was associated with a 17 percent reduction in death from CHD. More specifically, a 20 grams per day increase in fish consumption correlated with a 5.5 percent decrease in relative risk of CHD mortality. Consuming small quantities of fish was also associated with a 27 percent decreased risk in nonfatal myocardial infarction.
The same expert panel found a similar relationship between fish consumption and stroke risk. Consuming any amount of fish reduced the risk of stroke by 12 percent, compared to non-fish eaters, with a potential benefit of 2 percent reduction in risk for each additional serving per week.
Eating fish has an even greater impact on heart health in two recent prospective studies. The first was a study of more than 5,000 men and women from Finland who were followed for more than 20 years. Compared to women who consumed less than 8 grams of fish per day, the risk of CHD in women who consumed 9 to 15 grams, 16 to 24 grams, 25 to 40 grams, and more than 41 grams per day was reduced by 9 percent, 23 percent, 32 percent, and 41 percent, respectively. This research found no significant association between fish consumption and CHD in men, however.
In the Japan Public Health Center-Based Study of 41,578 Japanese men and women age 40 to 59 who were followed for about 10 years, those who consumed fish 8 times per week (median intake of 180 grams per day) had at least a 40 percent decrease in total CHD risk compared to those who consumed fish once per week (23 grams per day). The risk for total myocardial infarction was reduced by 56 percent in both men and women in this investigation.
Fishing for Evidence on Cancer
Numerous epidemiological studies and studies on animal models have suggested that diets high in omega-3 fatty acids may reduce the risk of certain types of cancer. However a recent systematic review of 38 studies did not agree with previous findings. Experts reviewed studies published from 1966 to October of 2005 involving 7 countries, 20 population cohorts, and 11 different types of cancer. They concluded that dietary supplementation with omega-3 fatty acids is unlikely to prevent cancer. Although these findings are disappointing, recent results from the European Prospective Investigation into Cancer and Nutrition (EPIC) study are very encouraging for a leading form of diet-related cancer: colon cancer.
This group of more than 40 researchers prospectively followed 478,040 men and women who were free of cancer at enrollment. After an average follow-up period of nearly 5 years, investigators found colorectal cancer was inversely associated with fish consumption. Those who ate more than 80 grams per day experienced a 31 percent decrease in colon cancer, compared to those who consumed less than 10 grams per day. The incidence of rectal cancer was even stronger, with a 51 percent decreased risk among fish eaters.
Investigators from Harvard have recently found that regularly consuming fish may significantly reduce the rate of colorectal cancer. Researchers examined fish intake in 22,071 Physicians’ Health Study participants who were followed for more than 19 years. Men who consumed five or more servings of fish per week had a 40 percent reduced risk of colorectal cancer, compared to men who ate fish less than once per week.
Benefits Far Outweigh The Risks
While the health benefits of omega-3 fatty acid intake are well recognized, concerns have been raised about potential harm from exposure to various associated contaminants, particularly mercury. Nearly all fish and shellfish contain traces of this heavy metal, and in 2004 the Food and Drug Administration and the Environmental Protection Agency advised women who may become pregnant, pregnant women, nursing mothers, and young children to avoid some types of fish and to eat fish and shellfish that are lower in mercury. However, a recent report published in the Journal of the American Medical Association concludes that the benefits of modest fish intake exceed the potential risks among adults. Researchers systematically reviewed reports published through April 2006 that evaluated intake of fish or fish oil and potential adverse effects of methylmercury, dioxins, and polychlorinated biphenyls (PCBs). “Avoidance of modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess CHD deaths annually . . . ,” they conclude.
Get Your Omega 3s
The richest source of omega-3 fatty acids is oily fish, which includes trout, salmon, mackerel, herring, fresh tuna (not canned), swordfish, and sardines. Those who are vegetarian or simply have an aversion to fish can get another type of omega-3 fatty acids called alpha linolenic acid (ALA) mainly from plant sources.
ALA can be converted in our bodies into EPA and DHA. Flax oil is an excellent source of ALA, containing approximately 40 to 60 percent ALA. And some foods, including eggs, have been enhanced with omega-3 fatty acids. Dietary supplements containing EPA and DHA are also readily available—and a good choice for anyone who doesn’t frequently consume food sources of omega-3 fatty acids.