Blood DHA Omega-3 Levels Inversely Associated with Stroke Risk
Saber, H. et al., Stroke, 48: 2678-2685, 2017
Dept. of Neurology, Wayne State University School of Medicine, Detroit, Michigan, USA
The present study was aimed at studying the relationship between blood levels of long-chain omega-3 fatty acids (a biomarker of omega-3 fatty acid status) and incident ischemic strokes. For this purpose, the research team included analyses of data and outcomes from three US-based cohort studies – the Cardiovascular Health Study (CHS) on older adults, the Nurses’ Health Study (NHS) on female registered nurses, and the Health Professionals Follow-Up Study (HPFS) on male health professionals. The fatty acid compositions (focus on long-chain omega-3 fatty acid levels in plasma phospholipid as isolated from the blood samples) were determined via gas-liquid chromatographic analyses of the fatty acid methyl esters following transmethylation. The median follow-up period was 11.2 years in the CHS subjects and 8.3 years in the pooled NHS and HPFS subjects. The occurrence of incident ischemic strokes was determined and, where possible, the identification of the stroke subtypes as ‘atherothrombotic’ and ‘cardioembolic’ was established. The former type occurs when a blood clot forms on an atherosclerotic plaque within a blood vessel in the brain and blocks blood flow to that part of the brain while the latter type is mostly found when a blood clot forms in subjects with atrial fibrillation and enters the bloodstream with subsequent arterial lodging to block blood flow to the brain. From the three combined cohort studies, a total of 54,992 blood samples were taken for analyses.
When compared to subjects in the lowest quartile (bottom 25 %) with respect to circulating DHA (docosahexaenoic acid) levels, those subjects in the highest quartile (top 25 %) exhibited an overall 20 % lower risk for total ischemic stroke and a highly significant 47 % lower risk for ‘atherothrombotic’ stroke with no significant relation to the ‘cardioembolic’ stroke subtype. EPA (eicosapentaenoic acid) levels did not correlate with the incidence of total ischemic stroke or either of the stroke subtypes. However, subjects in the highest quartile with respect to the level of circulating DPA (docosapentaenoic acid omega-3) exhibited a 26 % lower risk for total ischemic stroke and a 41 % lower risk for ‘cardioembolic’ stroke as compared to those with DPA levels in the lowest quartile.
The present study indicates that higher circulating levels of both DHA and DPA , but not EPA, appear to offer protection against total ischemic stroke with DHA showing particular protection against ‘atherothrombotic stroke’ and DPA against ‘cardioembolic stroke’. It is noted that ‘atherothrombotic stroke’ tends to predominate in prevalence. The potential mechanisms for the protective influence of DHA may include beneficial effects on multiple risk factors including the lowering of circulating triglyceride levels, resting heart rate, blood pressure, blood platelet aggregation, endothelial dysfunction along with reduced neuroinflammation in the brain. Since the present publication did not provide the absolute levels of DHA in the circulating blood biomarker, it is difficult to recommend a specific daily intake of DHA (mgs/day) that would ensure entry into the highest blood quartile. However, we previously showed (Conquer J. A, and Holub, B. J., J. Lipid Res., 39: 286-292 (1998)) that daily supplementation with 0.75 grams (750 mgs) of DHA/day increased DHA levels in the blood serum phospholipid by 167 % overall in a 8-week period which would most certainly be expected to place all subjects into the highest DHA quartile.