Effect of fish-oil supplementation on mental well-being in older subjects: a randomized, double-blind, placebo-controlled trial.

We hear all the time that fish oil is good for mood. So why did this study here not come to that conclusion?

302 seniors (independently living) were divided into 3 groups. The first group was dosed 1800 daily milligrams of EPA and DHA, the second group 400 milligrams, and the third group received placebo capsules. Before being given the capsules, and 13 and 26 weeks into the study, plasma concentrations of EPA and DHA as well as responses to several psychological tests were measured. Even though the fish oil significantly increased EPA and DHA concentration in the two dosed groups (by 238% in the high dose and 51% in the low dose), responses to the questionnaires were not significantly different. Why is that? There are probably several reasons.

1. Brain function is about a lot more than just omega-3 balance. Independently living seniors are likely to be eating an overall diet that is deficient in several nutrients. It would have been interesting to see a baseline blood test of other nutrient levels to see if overall nutritional status was correlated with test scores and EPA/DHA response.
2. The background diet of these seniors was not measured, or if it was, it was not reported. If, which is common because of convenience, the group as a whole was eating a lot of pre-prepared and packaged food, the ratio of pro-inflammatory oils to dietary omega-3 content may affect the outcome of the study.

It doesn't mean that just because there was not a mood-based response to these oils that they weren't beneficial. If levels of omega-3's increased dramatically, they most certainly were reducing cardiovascular risk, preventing the development of dementia and Alzheimer's, and improving bone health, to mention a few.

I just wish these researchers would understand the importance of controlling diet in any study that investigates the usefulness of an isolated supplement. Not only will it provide more significant results, it will keep people from mistakenly assuming that a certain nutrient is not of benefit when it actually is.

van de Rest O, Geleijnse JM, Kok FJ, van Staveren WA, Hoefnagels WH, Beekman AT, de Groot LC. Effect of fish-oil supplementation on mental well-being in older subjects: a randomized, double-blind, placebo-controlled trial. Am J Clin Nutr. 2008 Sep;88(3):706-13.