While omega-3 fatty acid deficiencies have been clearly linked to memory and learning problems in rodent models, studies involving dietary supplementation have produced mixed results. A contributing factor could be that the ratio of omega-3 and omega-6 fatty acids in the diet is a more important marker than omega-3 fatty acid intake alone. This hypothesis is based on the fact that these fatty acids share metabolic pathways, and on the assumption that they have compensatory or antagonistic effects.
What they did:
To test this hypothesis, scientists from the Cheatham Nutrition and Cognition Laboratory at the UNC Nutrition Research Institute looked at the omega-6: omega-3 ratio and as well as omega-3 levels in association with cognitive ability in children ages 7-12 years. Dietary intake was estimated from diet surveys; fatty acid levels in blood were measured directly. When analyzed across the entire child cohort, there were no significant correlations between fatty acid intake and cognitive ability. However, when children were separated into two age groups (7-9 y and 10-12 y), intriguing and statistically significant findings emerged.
Better performance was seen in younger children in the group who had the lowest omega-3 intake and the lowest omega-6: omega-3 intake ratio. However, better performance was seen in the older children in the group who had the highest omega-3 intake and the highest omega-6: omega-3 intake ratio. Similar results with plasma fatty acid levels were seen in the younger children, as lower plasma omega-6: omega-3 ratios predicted better performance on the more difficult cognitive tests. Correlations were weaker in the older children, although better performance was generally associated with higher plasma omega-3 levels.
What it means:
The results of this study shed light on the mixed conclusions of the value of dietary omega-3 supplements. It appears that one should consider both omega-6 and omega-3 intake when designing a study and interpreting its results. Additionally, associations of cognitive performance with omega-6: omega-3 ratio, omega-3 level, and socioeconomic status were stronger in the younger group, suggesting that diet during earlier development may be formative and/or that specific dietary needs differ with age.
Sheppard, KW & Cheatham, CL (2016). “Executive functions and the w-6 to w-3 fatty acid ratio: a cross-sectional study.” Am J Clin Nutr in press.