This study analyzed the relationship between multiple cognitive functions and dietary intake of fatty acids through a cross-sectional population-based study among middle-aged men and women living in the Netherlands. The 1,613 participants ranged from 45 to 70 years-old, 48% of whom were men. The participants were a part of the Doetinchem Cohort Study (DCS), a project that focused on monitoring cardiovascular disease risk factors. This current study used DCS's data from 1987 and 1991 as baseline measurements for its participant's dietary intakes between 1995 and 2000. The study not only hoped to use its findings to better understand how diet can affect the risk of Alzheimer's Disease, it also wanted to identify the signs of the effects in middle-aged people.
The researchers focused on the intake of cholesterol, saturated fat, fatty fish, total fat, monounsaturated fatty acids (MUFA), polyunsaturated fatty acid (PUFA), linoleic acid (an omega-6 PUFA), and three omega-3 PUFAs including docosahexaenic acid (DHA), eicosapentaeonic acid (EPA), and alpha-linoleic acid. The participants took a self-administered food frequency questionnaire to assess their diet intakes. To calculate the intake of each nutrient, researchers multiplied the frequency of consumption of a certain food by the portion size and the nutrient content per gram.
In order to assess the participants' cognitive functions, the researchers performed tests that measured the participants' memory function, speed of cognitive process, and cognitive flexibility. These tests, which were administered by trained investigators, included the (Visual) Verbal Learning Test, an abbreviated Stroop Color Word Test consisting of three sub-tasks, the Concept Shifting Task, the Letter Digit Substitution Task, and a Category Fluency Test. The results of these tests were used to create and compared to standardized Z-scores.
Confounders, including sex, age, education, smoking, alcohol consumption, and total energy intake, were also taken into consideration as to not misinterpret the results. The study also took the participants' family history of diseases into account.
While not statistically significant, researchers found that the risk of impairment in memory, speed, and flexibility was increased by 15% to 19% per standard deviation increase in saturated fat intake. Greater cholesterol intake significantly increased the risk of impaired memory and flexibility. On the other hand, the risk of impairment in overall cognitive function and speed decreased by 19% and 28% through EPA and DHA intake. The results for fatty fish consumption had an inverse relationship with cognitive function impairment, as well. There were not any clear associations between cognitive function and the intake of linoleic acid, total PUFA, alpha-linoleic acid, and MUFA.
This study seemed to truly focus on the impact that diet has on cognitive functions by taking all other variables into account. The study also incorporated a large pool of participants. One major concern of this study's methods, which was mentioned by the researchers, is that the participants' diets were based on self-administered questionnaires. It is unclear whether or not the participants experiencing cognitive function impairment were able to properly assess their diets. The study also did not expand on the procedures used during the cognitive function tests.
Kalmijn, S., Van Boxtel, M.P.J., Ocke, M., Verschuran, W.M.M., Kromhout, D., & Launer, L.J. (2004). Dietary intake of fatty acids and fish in relation to cognitive performance at middle age. Neurology, 62(2), 275-280. Retrieved from: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.580.4358&rep=rep1&type=pdf