It’s the golden age of omega-3 research. The February 2007 issue of the A merican Journal of Clinical Nutrition, perhaps the most prestigious nutrition journal, had two articles on the topic, the March issue seven (including four letters to the editor). The April issue has three (two research articles and an editorial), all on omega-3 and cognitive decline with age.
One was from Holland. Data were collected in 1990 and 1995 on 200-odd men, who were 70-89 in 1990. Those who ate fish had less cognitive decline from 1990 to 1995 than those who didn’t eat fish. A virtue of this paper is that the main results are shown graphically — a most basic point that AJCN papers usually get wrong.
The other study was done in Minneapolis. It looked at cognitive decline in about 2000 elderly men and women over a similar time period as the first study. Rather than asking subjects what they ate, this study measured blood levels of various fats. They did not find a reliable correlation between omega-3 levels and cognitive decline when considering all subjects but did find reliable (negative) correlations in subgroup analyses.
Both studies have selection problems. The first study looked at a small fraction of all the men in the study (total n = about 900) selected because of better health. I would have liked to see the results from the rest of the men. The second study did not correct for the vast number of significance tests done.
Both studies support — the second one quite weakly — the idea that omega-3s prevent cognitive decline. The main thing I notice is how difficult the research is. Data published 12 years after collection? Two thousand people studied twice, five years apart, with results barely different from noise?