By Jeremy Appleton, ND
Healthnotes Newswire —New data from the Nurses’ Health Study show that women who eat the most fish have a decreased risk of some types of stroke.1
Nearly 80,000 women between the ages of 34 and 59 were included in the 14-year follow-up study. Although many types of stroke appeared to be unaffected by fish intake, the risk of the most common type of stroke (called thrombotic infarction) was cut in half among women who ate fish at least twice per week, as compared with those who ate fish less than once per month. Fish consumption has been linked to reduced stroke risk in some,2 3 but not all,4 5 previous studies.
What component of fish makes it protective against stroke? Fish oil is rich in the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These omega-3 fatty acids, unlike the omega-3 fatty acid found in flaxseed oil and other vegetable oils (alpha linolenic acid), keep blood triglycerides in check (high triglycerides are generally linked with increased risk of heart disease) and inhibit the progression of atherosclerosis.6 In addition, EPA and DHA keep blood from clotting too quickly and have anti-inflammatory activity.
The authors of the new study also looked separately at the association between omega-3 fatty acid intake from fish and the incidence of stroke. They did find a protective association, but it was not as strong as the protective association from total fish intake. This suggests the possibility that some component of fish, in addition to omega-3 fatty acids, may help protect against thrombotic infarction.
Most of the protective effect from fish consumption occurred in people who did not also take aspirin. Although aspirin is considered protective against some types of stroke, its combination with fish and/or omega-3 fatty acids may not be desirable. The conversion of EPA into its biologically active forms requires an enzyme (called cyclo-oxygenase) that is blocked by aspirin. This may account for the lack of protection from stroke observed in people who both took aspirin and had high fish consumption.
Previous studies have raised the concern that omega-3 fatty acids in fish are blood thinners and may therefore increase the risk of strokes that involve bleeding (called hemorrhagic stroke). The new data show that high fish consumption does not put women at increased risk of hemorrhagic stroke. The effects of fish oil supplements on stroke prevention are not known and require further study.
References1. Iso H, Rexrode KM, Stampfer MJ, et al. Intake of fish and omega-3 fatty acids and risk of stroke in women. JAMA 2001;285:304–12.
2. Zhang J, Sasaki S, Amano K, et al. Fish consumption and mortality from all causes, ischemic heart disease, and stroke: an ecological study. Prev Med 1999;28:520–9.
3. Keli SO, Feskens EJ, Kromhout D. Fish consumption and risk of stroke. The Zutphen Study. Stroke 1994;25:328–32.
4. Orencia AJ, Daviglus ML, Dyer AR, et al. Fish consumption and stroke in men. 30-year findings of the Chicago Western Electric Study. Stroke 1996;27:204–9.
5. Morris MC, Manson JE, Rosner B, et al. Fish consumption and cardiovascular disease in the physicians’ health study: a prospective study. Am J Epidemiol 1995;142:166–75.
6. von Schacky C, Angerer P, Kothny W, et al. The effect of dietary omega-3 fatty acids on coronary atherosclerosis. A randomized, double-blind, placebo-controlled trial. Ann Intern Med 1999;130:554–62. Jeremy Appleton, ND, is a licensed naturopathic physician, writer, and educator in the field of evidence-based complementary and alternative medicine. Dr. Appleton is Chair of Nutrition at the National College of Naturopathic Medicine and Senior Science Editor at Healthnotes.