Fish and omega-3 fatty acids reduce risk of coronary heart disease in women
Studies have found that a higher consumption of fish and omega-3 fatty acids is associated with a reduced risk of coronary heart disease, but most of these studies have been conducted in men. The following paper examines this association in women.
Fish and omega-3 fatty acid consumption is associated with a reduced risk of coronary heart disease in women, particularly coronary heart disease death.
FB Hu et al. Fish and omega-3 fatty acid intake and risk of coronary heart disease in women. Journal of the American Medical Association 2002 287: 1815-1821.
Participants were 84,688 women, aged 34 to 59 years, from the US Nurses Health Study. Women with a history of cancer or a cardiovascular disease were excluded. Information on lifestyle and medical history was initially collected with questionnaires in 1976 and updated every two years. Diet was assessed with food frequency questionnaires administered in 1980, 1984, 1986, 1990 and 1994, which included four fish and seafood questions on dark meat fish (e.g. mackerel, salmon), tinned tuna, other fish, and shrimp, lobster and scallops. Serving sizes were 3-5 oz (84-140 g) for fish and 3.5 oz (68 g) for seafood. The women were divided into five categories according to frequency of fish consumption (less than once/month, 1-3 times/month, once/week, 2-4 times/week and five or more times/week) and quintiles of omega-3 fatty acid intake.
Participants were followed for incidence of coronary heart disease for 16 years. Cases were identified from various sources including medical records and state vital records and confirmed by several means, e.g. hospital records and autopsy reports. A total of 1,513 cases of coronary heart disease were documented (484 deaths and 1,029 nonfatal myocardial infarctions).
Compared with women who seldom ate fish, women with a higher fish consumption were less likely to smoke, more likely to be overweight, have hypertension, exercise, take multivitamins and regularly take aspirin. Fish consumption was positively associated with intakes of chicken, fruit, vegetables and dairy foods and inversely associated with intake of red meat.
Higher consumption of fish was associated with a reduced risk of total coronary heart disease. Compared with fish intake of less than once/month, risk of coronary heart disease decreased by 21% (1-3 times/month), 29% (once/week), 31% (2-4 times/week) and 34% (5+ times/week). The respective relative risks and 95% confidence intervals were as follows: 0.79 (0.64 to 0.97); 0.71 (0.58 to 0.87); 0.69 (0.55 to 0.88); 0.66 (0.50 to 0.89). Figure 1 shows the associations between fish consumption and risk of fatal coronary heart disease and nonfatal myocardial infarction.
Figure 1. Relative risks of fatal coronary heart disease and nonfatal myocardial infarction according to frequency of fish intake.
Similarly, higher intakes of omega-3 fatty acids were associated with a reduced risk of total coronary heart disease. Compared with the lowest quintile, quintiles three, four and five were associated with reduced risks of 22%, 32% and 33% respectively. The relative risks and 95% confidence intervals were as follows: 0.78 (0.65 to 0.93); 0.68 (0.56 to 0.82); 0.67 (0.55 to 0.81).
Both fish and omega-3 fatty acids were also associated with a lower risk of all-cause mortality (4,121 deaths from all causes were documented). Compared with fish consumption of less than once a month, eating fish at least 5 times a week reduced the risk of overall death by 32% (relative risk 0.68, 95% confidence interval 0.57 to 0.82). Compared with the lowest quintile of omega-3 fatty acid intake, the highest quintile was associated with a 25% reduced risk of overall death (relative risk 0.75, 95% confidence interval 0.67 to 0.85).
These results were adjusted for several lifestyle and cardiovascular risk factors (e.g. age, smoking, body mass index, alcohol intake, physical activity, history of hypertension and diabetes).
Women who consumed more fish also had a somewhat healthier diet and lifestyle. However, the results were adjusted for several lifestyle and cardiovascular risk factors and further analyses also adjusted for other dietary variables, such as trans-fats, fruit and vegetables, which did not appreciably alter the results. This suggests that fish and omega-3 fatty acids have an independent effect on coronary heart disease risk. (Other strengths of this paper include its prospective design, large sample size and repeated measures of dietary intake). The results also suggest that fish consumption is more protective against fatal coronary heart disease than nonfatal myocardial infarction.
This study examined the effect of long-chain omega-3 fatty acids, found predominantly in fish oil and the flesh of oil-rich fish (e.g. salmon, trout, kippers). The finding that both fish and omega-3 fatty acids are associated with a reduced risk of coronary heart disease is consistent with the hypothesis that omega-3 fatty acids are primarily responsible for the apparent protective effect of fish. The mechanisms by which omega-3 fatty acids may reduce coronary heart disease include reduction of serum triglycerides, platelet aggregability and anti-arrhythmic effects.
This study in women is welcome, and broadly parallels results found in men in Finland, Italy and Holland, that eating small amounts of oily fish a week substantially reduces the risk of coronary death, and similar results from the United States.