Eating fatty fish and marine omega-3 fatty acids, which are found in fish oil, seems to protect men from heart failure according to one of the largest studies to investigate the association.
However, the effect was seen only in men who eat approximately one serving of fatty fish a week and who had a moderate intake of marine omega-3 fatty acids (approximately 0.3 grams a day). Eating more did not give a greater benefit and, in fact, returned the chances of heart failure to the same level as that seen in men who never consume fatty fish or fish oils.
The study provided no evidence that taking food supplements containing marine omega-3 fatty acids made any difference. The men in this study, which is published in Europe's leading cardiology journal, the European Heart Journal [1] today (Wednesday 22 April), obtained most of their marine omega-3 fatty acids from the food they ate.
Researchers in the USA and Sweden followed 39,367 Swedish men, aged between 45-79, from 1998 to 2004. They recorded details of the men's diet and tracked the men's outcome through Swedish inpatient and cause-of-death registers. During this period, 597 men without a history of heart disease or diabetes developed heart failure, of which 34 died.
The researchers found that men who eat fatty fish, such as herring, mackerel, salmon, whitefish and char, once a week were 12% less likely to develop heart failure compared to men who never eat fatty fish. Although this association with fatty fish did not reach statistical significance, the researchers also found a statistically significant association with the intake of marine omega-3 fatty acids (found in cod livers and other fish oils); men who consumed approximately 0.36 grams a day were 33% less likely to develop heart failure than men who consumed little or no marine omega-3 fatty acids (0.15-0.22 grams a day). [2]
The men were divided into five groups depending on their intake of fatty fish, with the first group consuming none, or very little, and the fifth group consuming the most - three of more servings of fatty fish a week. The researchers found that while the middle group, which eat one serving of fatty fish a week, had a 12% reduced risk compared to the men who never eat fatty fish, the men in the next two groups, who eat either two servings a week or three or more servings a week, had nearly the same risk as the men who eat none.
The researchers also divided the men into five groups based on their intake of marine omega-3 fatty acids. Again, the same U-shape was seen, with the middle group who consumed 0.36 grams a day of fatty acids having a 33% reduced risk of heart failure, while the men who consumed more (either approximately 0.46 grams per day or approximately 0.71 grams per day) had a risk similar to men who consumed none or very little.
Dr Emily Levitan, a cardiology research fellow at Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, USA, who led the research, said: "Our study shows that a moderate intake of fatty fish and marine omega-3 fatty acids is associated with lower rates of heart failure in men, but that the men did not gain a greater benefit by eating more of these foods.