Previously on this site, for example here, I have written about the evidence which supports the idea that fish is what might be regarded as ‘brain food’. The study highlighted in that particular blog showed that high levels of DHA (docosahexaenoic acid – a so-called omega-3 fat found in certain species of fish) were associated with a substantially reduced risk of dementia and Alzheimer’s disease in the elderly. This sort of study cannot be used to prove that it is DHA that is the critical factor. However, it is known that DHA makes up a significant proportion of the fat found in the nerve cell membranes in the brain. With this in mind, it’s not too difficult to imagine that ensuring good levels of DHA in the body and brain might be important to brain function.
The link between fish and omega-3 levels and brain function have recently been re-examined again in two studies that appear in this month’s edition of the American Journal of Clinical Nutrition. In one of these studies, the relationship between fish intake and brain function (as measured by a battery of tests) was assessed in a group of more than 2000 Norwegians aged 70-74 [1]. The researchers found that eating an average of 10 g or more of fish a day, compared to eating less fish than this, was associated with better brain function and lower risk of being rated with ‘poor cognitive performance’.
One thing that strengthens the idea that it’s something in the fish that doing good here is the fact that there was what is known as a ‘dose-response’ relationship between fish intake and brain function: In other words, the more fish that was eaten, the better the brain function. This relationship held up to an intake of 75 g a day, after which there appeared to be no additional benefit.
In the second study, researchers measured blood levels of omega-3 fats in more than 800 men and women aged 50-70, and compared these to brain function (again, measured with a battery of tests) [2]. The participants of this study were assessed over a 3-year period. Over time, individuals with higher body levels of omega-3 fats were found to be significantly less prone to decline in two tests of cognitive performance (sensorimotor speed and complex speed). However, there was no relationship found between omega-3 levels and other tests of brain function including memory and word-fluency.
The authors of this second study call for potential for omega-3 fats to preserve or enhance brain function to be assessed with randomised controlled trials. This means treating a population with omega-3 fats, and comparing the effects of this over time with placebo (inactive agent). Such research, if properly conducted, would help settle one and for all whether omega-3 fats can help preserve brain function as we age.
While randomised controlled trials in this area have yet to be published, there is however a fair volume of work which has assessed the affects of omega-3 supplementation on depression and even bipolar disorder (once known as manic depression). A recent analysis of 10 relevant studies found that, compared to placebo, omega-3 fats were found to have significant antidepressant effect [3]. Taken as a whole, I believe the bulk of the evidence suggests that omega-3 fats have genuine benefits for the brain. And let’s not forget that these fats appear to have considerable ability to ward of physical ailments too ” particularly with regard to cardiovascular disease. Good sources of omega-3 fats include salmon, trout, mackerel, herring and sardine. For a guide to the most sustainable fish in our seas, see http://www.fishonline.org.
References:
1. Nurk E, et al. Cognitive performance among the elderly and dietary fish intake: the Hordaland Health Study. Am J Clin Nutr. 2007;86(5):1470-8.
2. Dullemeijer C, et al. n 3 Fatty acid proportions in plasma and cognitive performance in older adults. Am J Clin Nutr. 2007;86(5):1479-85.
3. Lin PY, et al. A meta-analytic review of double-blind, placebo-controlled trials of
antidepressant efficacy of omega-3 fatty acids. J Clin Psychiatry. 2007;68(7):1056-61.
