(Reuters Health) - Women who eat more than three servings of fish per week are less likely to experience a stroke, a new study suggests.
Specifically, fish-lovers in Sweden were 16 percent less likely to experience a stroke over a 10-year-period, relative to women who ate fish less than once a week.
"Fish consumption in many countries, including the U.S., is far too low, and increased fish consumption would likely result in substantial benefits in the population," said Dr. Dariush Mozaffarian of the Harvard School of Public Health, who reviewed the findings for Reuters Health.
When choosing fish to eat, it's best to opt for fish that are rich in omega-3 fatty acids, found most abundantly in fatty fish like salmon, mackerel and albacore tuna. "But any fish is better than none," Mozaffarian noted.
Indeed, these fatty acids likely underlie the benefits of fish on stroke risk, study author Dr. Susanna Larsson of the Karolinska Institute in Stockholm told Reuters Health. "These fatty acids may reduce the risk of stroke by reducing blood pressure and blood (fat) concentrations."
This is not the first study to suggest that people who eat more fish have a lower risk of stroke, and experts already recommend a fishy diet to reduce the risk of cardiovascular problems, Mozaffarian added. "This study supports current recommendations."
Earlier this year, for instance, a study showed that middle-aged and older men who eat fish every day are less likely than infrequent fish eaters to develop a suite of risk factors for heart disease, diabetes and stroke.
In the current study, published in the American Journal of Clinical Nutrition, Larsson and her colleagues looked at 34,670 women 49 to 83 years old. All were free of cardiovascular disease and cancer at the beginning of the study, in 1997.
During 10 years of follow-up, 1,680 of the women (4 percent) had a stroke.
Stroke caused by blockage of an artery that supplies blood to the brain -- also known as a "cerebral infarction" or "ischemic stroke" -- was the most common event, representing 78 percent of all strokes in the study. Other types of strokes were due to bleeding in the brain, or unspecified causes.
Women who ate more than three servings of fish per week had a 16 percent lower risk of stroke than women who ate less than one serving a week. "Not a small effect," Mozaffarian said in an e-mail, noting that it was roughly equivalent to the effect of statin drugs on stroke risk. Furthermore, the researchers asked women about their diets only once, using a questionnaire, which might have caused errors that would underestimate the link between a fishy diet and stroke risk, he explained. "So, the true risk reduction may be larger."
Interestingly, women appeared to benefit most from eating lean fish, when other research shows fatty fish is better for health. This finding may stem from the fact that most fatty fish, such as herring and salmon, is eaten salted in Sweden, Larsson explained. "A high intake of salt increases blood pressure and thus may increase the risk of stroke," she said in an e-mail. "So the protective effects of fatty acids in fatty fish may be attenuated because of the salt."
Indeed, when it comes to fish, not all have equal benefits, Mozaffarian noted - for instance, he said, research has not shown any cardiovascular benefits from eating fast food fish burgers or fish sticks.
In addition, women of childbearing age should avoid certain types of fish known to carry relatively high levels of pollutants, such as shark and swordfish, Mozaffarian cautioned. "This is a very, very short list of fish to avoid or minimize -- there are many, many other types of fish to consume," he said. "Women at risk of stroke are generally beyond their child-bearing years, and so for these women, all types of fish can be consumed."
Larsson and her team speculate that certain nutrients in fish, such as fatty acids and vitamin D, might explain its apparent benefits. The Swedish study cannot prove cause and effect for high fish consumption and lowered stroke risk, however. For instance, fish consumption could be a sign of a generally healthier lifestyle or some other mechanism at work.
Last December, Larsson and colleagues published data from the same group of women in the journal Stroke showing that those who eat a lot of red meat may also be putting themselves at increased risk of stroke.