Purpose of study: Observe how plasma n-3 fatty acids affect risk of cognitive decline in older adults.
Research methodology: Prospective human observational cohort study
Description: Beydoun et al (1) analyzed plasma fatty acids in cholesteryl esters and phospholipids in 2,251 white women and men ages 50-65 from 1987 to 1989 in a community in Minneapolis, MN. In subsequent years 1990 to 1992 and 1996 to 1998, researchers administered cognitive tests on the subjects.
Measurements: Blood analysis was performed through collection of 12-hour fasting blood followed by identity of peaks through gas chromatography. Reliability coefficient for the testing ranged from 0.50 to 0.93 for cholesteryl esters and from 0.50 to 0.89 for phospholipids.
Cognitive assessments included tests for delayed word recall, psychomotor speed and verbal fluency. The researchers properly noted that almost all subjects had education of high school or above, which was important to assure group comparability. Ages 65 and older were excluded to as not skew measurements as were those showing signs of early mental decline.
Problems: Disadvantages of this study were chiefly the amount of confounding variables, which required control through backward elimination. Despite the control and reducing subjects from initial 4,000 to the 2,251, the large amount of subjects introduced many covariates. As appropriate Beydoun et al reported a type 1 error level of 0.10 that was validated through statistical analysis.
Results: Study’s findings suggested n-3 fatty acids “may have substantial benefits in reducing risk of cognitive decline in the area of verbal fluency,” but did not suggest any benefit for psychomotor speed or delayed word recall. Further, findings revealed warranted enrichment of n-3 fatty acids in the diet of those with increased oxidative stress from hypertensive and dyslipidemia.
Assessment: Despite noteworthy effort on behalf of Beydoun et al to control variables by reducing the study to a homogenous population and by eliminating many covariates, the other multivariates acting as potential confounders leads me to agree with the researchers themselves that randomized, controlled, cross-over trials are necessary to determine more meaningful data.
Reference: Beydoun MA, Kaufman JS, Satia JA, Rosamond W, Folsom AR. Plasma n-3 fatty acids and the risk of cognitive decline in older adults: the Atherosclerosis Risk in Communities Study. Am J Clin Nutr 2007;85:1103-11. Available at: http://www.ajcn.org/cgi/content/full/85/4/1103.