Food: Fish once a week may keep sudden heart attacks at bay, says study

Eating fish once a week can halve the risk of dying suddenly from a heart attack, according to a new study. But how reliable is the finding? Jeremy Laurance, Health Editor, unravels a complex story.

A study of 20,000 male American doctors suggests that fish may have a more dramatic effect on the heart than has been suspected. Those who ate fish of any kind at least once a week had a 52 per cent lower risk of sudden death from heart disease than those who ate it less than once a month.

But the finding is complicated by the apparent absence of any other protective effects of fish on the heart. There was no difference between the frequent fish eaters and the rest in terms of the number of heart attacks, deaths from heart disease or non-sudden cardiac deaths.

Oily fish - salmon, mackerel and others containing what are thought to be the most beneficial omega-3 fatty acids - had a protective effect against sudden death but it was not as great as that from overall fish consumption.

Christine Albert and colleagues from the Brigham and Women's Hospital in Boston, Massachusetts, say in the Journal of the American Medical Association that 250,000 sudden heart deaths occur in the United States each year, more than half of which have no previous history of heart disease.

"All levels of fish consumption were associated with a decreased risk of sudden death, but the size of the reduction did not appear to differ substantially at levels of consumption greater than one fish serving per week, suggesting a threshold effect."

Doubts about the study are raised in an accompanying editorial by Daan Kromhout, of the National Institute of Public Health in the Netherlands. The findings conflict with other studies, which have shown protective effects against heart disease deaths but not against sudden cardiac deaths, and the number of doctors eating fish less than once a month was very small, suggesting other characteristics could account for their higher risk of sudden death.

Dr Kromhout said evidence accumulated over 20 years showed clearly that non-fish eaters were at higher risk of dying of heart disease. Attention has focused on oily fish such as mackerel because it contains the highest levels of omega-3 fatty acids which are believed to be important in preventing the ventricular fibrillation (heart flutter) that is thought to trigger heart attacks.

"The more unsaturated the fatty acids the stronger the effect. That is the hypothesis we are working on," Dr Kromhout said.