Eating fatty fish no more than once a week, and an intake of about 0.3 grams per day of marine omega-3 fatty acids, appear to reduce the risk of heart failure in middle-aged and elderly Swedish men.

The associations derived from the Cohort of Swedish Men were U-shaped, however, with lesser or greater consumption showing no protective effects, Dr. Emily B. Levitan and associates report in the European Heart Journal.

Levitan, at Beth Israel Deaconess Medical Center in Boston, and her co-researchers studied data on more than 39,000 men, ages 45-79 years, in central Sweden who completed food intake questionnaires at the start of the study.

Herring, mackerel, salmon, whitefish, and char were considered fatty fish. Marine omega-3 fatty acids were derived from food sources or consumed as supplements.

Over an average followup of seven years, heart failure developed in 597 subjects.

Eating fatty fish once per week versus not at all reduced the risk of heart failure by about 12 percent, although the association was not significant from a statistical standpoint.

By contrast, the association between marine omega-3 fatty acids and heart failure was significant, with the lowest risk seen among those in the middle range of intake, that is, 0.32-0.40 grams per day.

To explain the lack of benefit at higher levels of consumption, Levitan’s team speculates that if men in poor health ate more fatty fish and marine omega-3 fatty acids, then these substances could appear to be risk factors for HF.

Another possibility is that the levels of mercury and organic contamination of fish can be very high in some parts of Sweden, which could raise the risk of heart disease and offset the benefit of fatty acids.

SOURCE: European Heart Journal, April 22, 2009.