Circulating biomarkers of dairy fat and risk of incident stroke in US men and women in 2 large prospective cohorts

Background: Previous observational studies of self-reported dairy product consumption and stroke risk have reported mixed findings. Few studies have used circulating biomarkers that provide objective measures of dairy fat intake. Objectives: We tested the hypothesis that the circulating biomarkers of dairy fat, pentadecanoic acid (15:0), heptadecanoic acid (17:0), and trans palmitoleate (trans 16:1 n-7), were associated with lower incidence of stroke, especially ischemic stroke. Secondarily, we evaluated 14:0, which is obtained from dairy products and beef, and also endogenously synthesized. Design: In participants from 2 large US cohorts (the Health Professionals Follow-Up Study: 51,529 men; the Nurses' Health Study: 121,700 women) with stored blood samples in 1993-1994 (n = 18,225) and 1989-1990 (n = 32,826), respectively, we prospectively identified 594 incident stroke cases (median follow-up: 8.3 y) and matched them 1:1 to risk-set sampled control subjects by age, sex, race, and smoking. Total plasma and red blood cell (RBC) fatty acids were measured by using gas-liquid chromatography. Covariates were assessed by using validated questionnaires. Stroke events and subtypes were adjudicated by using medical records or other supporting documentation. We used conditional logistic regression to estimate associations of fatty acids with incident stroke, and cohort-specific findings were combined by inverse-variance weights. Results: After adjustment for demographic characteristics, lifestyle, cardiovascular disease risk factors, diet, and other circulating fatty acids, no significant associations with total stroke were seen for plasma 15:0 (pooled HR for highest compared with lowest quartiles: 0.85; 95% CI: 0.54, 1.33), 17:0 (0.99; 0.67, 1.49), trans 16:1 n-7 (0.89; 0.55, 1.45), or 14:0 (1.05; 0.62, 1.78). Results were similar for ischemic and hemorrhagic stroke subtypes, for RBC fatty acids, and in several different sensitivity analyses. Conclusion: In 2 large prospective cohorts, circulating biomarkers of dairy fat were not significantly associated with stroke.