Background Diet plays an important role in the pathogenesis of Alzheimer’s disease (AD). Dietary fatty acids that are not synthesized in humans may serve as tissue markers for intakes of those source foods. A growing body of evidence supports that erythrocyte pentadecanoic acid (15:0) is a potential biomarker for dairy intake.Objective To investigate the associations between dairy intakes, erythrocyte 15:0, and cognitive function among elderly participants in the Cache County Study on Memory, Health and Aging.Design Erythrocyte fatty acids were profiled as a percentage of total fatty acids for 1987 nondemented subjects. Cognitive function was assessed with an adapted Modified Mini‐Mental State examination (3MS). Food intakes were surveyed with a 142‐item food frequency questionnaire and were adjusted by total energy using the residual method. Spearman partial correlations adjusted for age, gender and BMI were examined for erythrocyte 15:0, intake of individual dairy product, and 3MS score. Multivariable linear regression models were fit on dairy intakes with erythrocyte 15:0 as the outcome controlling for potential confounding factors.Results Erythrocyte 15:0 was positively associated with dietary intakes of 1‐2% milk (r = 0.12, p < 0.001), whole milk (r = 0.28, p = 0.001), butter (r = 0.16, p < 0.001), and cheese besides Cottage/Ricotta or cream cheese (r = 0.12, p < 0.001) but was not associated with the intakes of skim/chocolate milk, (frozen) yogurt, ice cream, and Cottage/Ricotta/cream cheese. In multivariable regression models each increase in servings of whole milk, butter, 1‐2% milk, and cheese besides Cottage/Ricotta or cream cheese was associated with a 0.30, 0.16, 0.13, and 0.12 points increase on the erythrocyte 15:0 (p < 0.001 for all). Erythrocyte 15:0 was not correlated with 3MS score.Conclusion Erythrocyte pentadecanoic acid is a biomarker for the consumption of less modified dairy products and is not correlated with 3MS score in elderly adults living in Northern Utah.Grant Funding Source: Supported by Dairy Research Institute