Recent research indicates that n–3 fatty acids can inhibit cognitive decline, perhaps differentially by hypertensive status.

We tested these hypotheses in a prospective cohort study (the Atherosclerosis Risk in Communities). Dietary assessment using a food-frequency questionnaire and plasma fatty acid exposure by gas chromatography were completed in 1987–1989 (visit 1), while cognitive assessment with three screening tools – the Delayed Word Recall Test, the Digit Symbol Substitution Test of the Wechsler Adult Intelligence Scale–Revised and the Word Fluency Test (WFT) – was completed in 1990–1992 (visit 2) and 1996–1998 (visit 4). Regression calibration and simulation extrapolation were used to control for measurement error in dietary exposures.

Four US communities – Forsyth County (North Carolina), Jackson (Mississippi), suburbs of Minneapolis (Minnesota) and Washington County (Maryland).

Men and women aged 50–65 years at visit 1 with complete dietary data (n = 7814); white men and women in same age group in the Minnesota field centre with complete plasma fatty acid data (n = 2251).

Findings indicated that an increase of one standard deviation in dietary long-chain n–3 fatty acids (% of energy intake) and balancing long-chain n−3/n–6 decreased the risk of 6-year cognitive decline in verbal fluency with an odds ratio (95% confidence interval) of 0.79 (0.66–0.95) and 0.81 (0.68–0.96), respectively, among hypertensives. An interaction with hypertensive status was found for dietary long-chain n–3 fatty acids (g day−1) and WFT decline (likelihood ratio test, P = 0.06). This exposure in plasma cholesteryl esters was also protective against WFT decline, particularly among hypertensives (OR = 0.51, P < 0.05).

One implication from our study is that diets rich in fatty acids of marine origin should be considered for middle-aged hypertensive subjects. To this end, randomised clinical trials are needed.