Associations and Effects of Omega-3 Polyunsaturated Fatty Acids and Other Dietary Constituents on Cognitive Function and Mood in Healthy Adults

Omega-3 Polyunsaturated Fatty Acids (PUFAs),from oily fish, have been associated with brain health benefits. This thesis investigated associations between omega-3 PUFAs and cognitive and mood function in healthy adulthood using three studies. Study 1 systematically reviewed previous studies addressing the associations ofomega-3-PUFA intake and/or blood levels with cognition and mood. In total eighty studies, 53 observational prospective cohort studies and 27 randomised controlled trials (RCTs),were included in the qualitative synthesis, and 58(37 cohort,21 RCTs)in the quantitative synthesis. Pooled analyses of cohort studies revealed that higher omega-3 PUFAs levels/intake was associated with a lower risk of dementia, improved executive functioning, and lower levels of depressive symptoms. Pooled analyses of RCTs did not demonstrate any consistent effects of omega-3 PUFAs on cognition/mood. However, the RCTs had considerably smaller sample sizes, and shorter follow-up durations, than did the cohort studies. Study 2 explored cross-sectional associations between blood levels of omega-3 PUFAs, homocysteine, vitamin D and empirically derived dietary patterns with cognitive function and mood, in 159 healthy adults. Omega-3 PUFA levels were positively associated with intelligence quotient and inversely associated with information processing speed. Higher vitamin D levels were associated with faster psychomotor speed and lower levels of depression. Principal components analysis on dietary questionnaire data revealed 3 dietary patterns, representing diets rich in (1) processed foods, (2) animal sourced foods and (3) fruits and vegetables. The processed foods dietary pattern was positively associated with anxiety. Study 3 was a 6-month double-blind RCT examining the effects of omega-3 PUFA enriched chicken meat and/or eggs on cognitive function and mood in 140 healthy adults. Although the intervention increased blood levels of omega-3 PUFAs, this was not accompanied by improvements in cognition/mood. Future RCTs should be sufficiently powered and consider the quality and duration of theiromega-3 PUFA interventions.