n-3 Fatty acids, hypertension and risk of cognitive decline among older adults in the Atherosclerosis Risk in Communities (ARIC) study

Abstract

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

Design: 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.

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

Subjects: 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).

Results: 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).

Conclusion: 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.

Figure 1. SIMEX plot of corrected coefficients for stratified models 3b and 3e of Table 3; ARIC (1987-98)*

*pct3h: dietary intake of long chain n-3 fatty acids expressed as percentage of energy intake (3H); r3hr6h: ratio of long chain n-3 to long chain n-6 fatty acids (3H/6H). Lambda is equivalent to θ = {0.5, 1, 1.5, 2} and is a scale factor used to add error to the covariate and estimate βm= f(θ,βm) starting from the naïve estimate in which θ = 0. Hence, the naïve estimate of the regression coefficient β is the one estimated by generalized linear models without measurement error correction. See online Appendix for more details.