Abstract P277: Circulating Plasma Dairy Fatty Acid Biomarkers and Incident Stroke in Two US Prospective Cohort Studies

Background: Prior observational studies suggest that self-reported consumption of dairy foods is associated with lower risk of stroke. Few studies have used circulating biomarkers that provide objective measure of dairy consumption. AIM: To test the hypothesis that plasma fatty acid biomarkers of dairy, 15:0, 17:0 and 16:1 n-7t, are associated with lower risk of incident stroke, especially ischemic stroke. Methods: We performed nested case-control studies in two prospective cohorts, the Nurses Health Study (NHS) and Health Professionals Follow Up Study (HPFS). Blood collected in 1989-90 (NHS) and 1993-94 (HPFS) was used to measure plasma 15:0, 17:0 and 16:1 n-7t biomarkers that are not endogenously synthesized. Stroke was prospectively adjudicated using medical records through 2004. A total of 597 stroke cases (NHS:475, HPFS:122), including 454 ischemic, 122 hemorrhagic and 21 unknown type, were matched 1:1 with controls on age, race, smoking, blood collection date and follow-up time (risk set sampling). Conditional logistic regression was used and cohort findings pooled by fixed-effects meta-analysis. Results: 15:0 was correlated with self-reported intakes of whole fat dairy foods (r=0.18 in NHS, r=0.18 in HPFS), low fat dairy (r=0.13, 0.11) and dairy fat (r=0.20, 0.30). 17:0 and 16:1 n-7t were less strongly correlated. After confounder adjustment, comparing the top vs. bottom quartiles, 15:0, 17:0 and 16:1 n-7t were not significantly associated with total or ischemic stroke in either cohort or overall ( Table 1 ). Results were similar after simultaneous adjustment for the 3 dairy fat biomarkers and for potential mediators. Conclusion: In these 2 cohorts, circulating dairy fat biomarkers were not significantly associated with stroke. Possible explanations include no true association, insufficient statistical power or measurement error due to changes in exposure over time. This study emphasizes need for further research on dairy and stroke using objective biomarkers, including studies with serial measures.