Eating fish regularly reduced the risk of heart disease in diabetic women by as much as 64 per cent, according to an American study out today.
"We found that women with type 2 diabetes who ate more fish had significantly lower risk of coronary heart disease and total death than those who rarely ate fish," said Dr Frank B. Hu, lead author and associate professor of nutrition and epidemiology at the Harvard School of Public Health in Boston.
His findings support previous research that has found fish consumption to reduce the risk of heart disease in a largely healthy population. But this is the first study to look at the relationship among diabetic patients, who have a very high risk of heart disease.
National health associations usually recommend that adults, except pregnant women, eat two servings of fish a week. The researchers suggest that for those with, or at high risk of cardiovascular disease (CVD), supplementing fish in the diet with fish oil capsules may be advisable in consultation with a doctor.
Omega-3 fatty acids from fish have been shown to reduce the risk of irregular heartbeats that can lead to sudden death, decrease blood triglyceride levels, improve the functions of blood vessels and reduce blood clot formation - all important factors in reducing risk for heart disease among diabetics.
However there is little prior evidence confirming that diabetics who eat fish can gain the same benefits as people without diabetes who eat fish, Hu said, writing in the rapid access issue of Circulation, the American Heart Association journal. The researchers were also concerned that fish oil might worsen control of blood sugar among diabetic patients.
Hu and colleagues analysed data from women with diabetes participating in the Nurses' Health Study (lifestyle and medical history data on more than 121,000 female nurses). They found 5,103 women had reported type 2 diabetes at any time from 1976-94. Women with a history of heart disease, stroke or cancer reported on the 1980 questionnaire (when diet was first assessed) or before they were excluded.
The women were divided into five categories according to how often they ate fish: less than once a month, one to three times a month, once a week, two to four times a week, and five or more times a week.
Between 1980-96, the researchers documented 362 cases of heart disease. They found that diabetic women who ate fish at least once a month were older, slightly heavier, typically did not smoke, tended to have hypertension and high cholesterol, and took multivitamin and vitamin E supplements. Those who ate more fish also ate more fruits and vegetables but ate less red and processed meats.
Compared with diabetic women who seldom ate fish (less than once a month), the risk of developing heart disease was reduced on average by 30 per cent in those who ate fish one to three times a month, 40 per cent for those who ate it once a week, 36 per cent in those who ate fish two to four times a week, and 64 per cent in those who ate fish five or more times a week. Higher fish consumption was also associated with a significantly lower death rate.
Hu suggested that the association between higher fish consumption in diabetic women and better heart health can also be extended to diabetic men based on similar findings in studies of healthier men and women.
However he admitted that the study was limited because it was not a randomised clinical trial. "Thus, the benefits we observed for fish may be due to other dietary and lifestyle factors related to fish intake," he said.Even so, Hu argued that their findings are solid because of their "careful adjustment for many important cardiovascular risk factors."
The team concluded that regular fish consumption should be considered as part of a healthy diet for diabetes management, with at least two servings weekly for individual patients. Fatty fish such as mackerel, lake trout, herring, sardines, albacore tuna and salmon are high in omega-3 fatty acids.
In an accompanying editorial, Dr Scott M. Grundy, director of the Center for Human Nutrition at the University of Texas Southwestern Medical Center at Dallas, said Hu's research supports previous studies on omega-3 fatty acids. However, he urged that clinical trials of omega-3 fatty acids after a heart attack be conducted to determine if they can reduce coronary deaths in the short term.
In the 8 February issue of The Lancet, researchers reported that Omega-3 fatty acids apparently reduced the build up of atherosclerosis and helped to stabilise the health in stroke patients who are at high risk of atherosclerotic plaques rupturing or forming clots.