Fish and omega-3 fatty acid intake and risk of stroke
Several, but not all, studies have shown that fish consumption protects against stroke. This study takes the research a step further and examines the relationship between fish and omega-3 polyunsaturated fatty acid intake and risk of stroke subtypes.
This study was unable to further our understanding of the association between intake of fish, omega-3 polyunsaturated fatty acids and stroke risk. Nevertheless, omega-3 fatty acids (found in cold water fish such as mackerel, herring, halibut and salmon) have many vital roles, for example they are essential for normal nerve impulse transmission and brain function. The advice to eat one portion of these fish a week is important for other reasons, like heart attack survivability .
H Iso et al. Intake of fish and omega-3 fatty acids and risk of stroke in women. Journal of the American Medical Association 2001 285: 304-312.
Participants were 79,839 women, aged 34 to 59 years, from the US Nurses' Health Study, with no previous diagnosis of cardiovascular disease, cancer, diabetes or hypercholesterolemia. In 1980 questionnaires assessed their lifestyle and medical history (which was updated every two years) and their diet (which was re-examined in 1984, 1986 and 1990). The women were followed for 14 years. Intakes of fish and long chain omega-3 fatty acids were calculated and the latter divided into quintiles. Strokes were confirmed by medical records according to the criteria of the National Survey of Stroke.
A total of 574 cases of stroke were reported: 119 subarachnoid hemorrhages, 62 intraparenchymal hemorrhages, 303 ischaemic strokes (264 thrombotic and 39 embolic) and 90 strokes of undetermined type. Of the thrombotic infarctions, 90 were large-artery occlusive infarctions and 142 were lacunar infarctions.
There was no association between fish intake and total stroke. Of the stroke subtypes, eating fish two or more times a week was associated with a reduced risk of lacunar infarction (relative risk 0.28, 95% confidence interval 0.12 to 0.67) compared with eating fish less than once a month (based on 14 cases). These results were adjusted for age, smoking, other cardiovascular risk factors (e.g. body mass index, exercise) and dietary variables (e.g. saturated fat intake).
Women in the highest quintile of omega-3 fatty acid intake had a reduced risk of total stroke compared with women in the lowest quintile (relative risk 0.72, 95% confidence interval 0.53 to 0.99). Of the stroke subtypes, the highest quintile of omega-3 fatty acids was associated with a reduced risk of lacunar infarction (relative risk 0.37, confidence interval 0.19 to 0.73) compared with the lowest quintile (based on 19 cases).
The few associations that were found in this study were based on a small number of stroke cases and there was no consistency among the associations observed. For example, an association was found between the highest intake of omega-3 fatty acids and risk of total stroke, but only one association was found among the seven subtypes of stroke.
Based on these results the association between fish and omega-3 polyunsaturated fatty acid intake and stroke risk is still open to question. The effect looks small, but a larger number of stroke cases are needed to provide a more definitive answer.