Another one for the marine-derived highly unsaturated fatty acids are probably really important for proper brain function files: This new paper has been tweeted quite a bit lately: Suicide Deaths of Active Duty US Military and Omega-3 Fatty Acid Status: A Case-Control Comparison
It is an observational study, but large for a suicide study (suicide is, fortunately, quite rare). All told, 800 randomly selected suicide victims in the armed services were selected between 2002-2008, and compared to 800 matched controls. Cases were matched for time and theater of deployment, exposure to stress during deployment, report of mental health status, and demographics among other data points. (Though later the paper says 99.1% of the controls had been deployed vs. only 61.9% of the suicides, so the deployment location and duration were not added as covariates to the end calculations).
So, fatty acid of the blood of the participants - in short, the lower the DHA in the blood, the more likely the person was to have committed suicide. The relationship was linear and true of all octiles studied. There were only 70 women in the samples, and they tended to have higher DHA levels than the men, and lower suicides (among women, the omega 3 status to suicide relationship was not statistically significant as it was clearly so among the men). Men in the lowest DHA octile were 62% more likely to commit suicide than those in the highest octile.
Other fatty acids of interest - lower levels of stearic acid (saturated! My goodness! Found in chocolate! And steak!) were found to be associated with increased risk of suicide (my preliminary conclusion - eat more chocolate - though it is only observational - I'll risk it and eat your chocolate if you are uncertain). Also, higher palmitoleic acid (a monounsaturated acid made from the saturated palmitic acid) levels correlated with a lower level of suicide risk.
In this study, US military personnel were found to have, on average, a lower DHA level than average North American, Australian, Mediterranean, and Asian populations (unlike the medical students I wrote about a few articles ago, who had higher levels than the general population). In fact, among Chinese suicide attempters, nearly all of them had higher levels of omega 3 DHA than the highest octile of the US military personnel studied. And when both populations were studied together, the lowest DHA levels coincided with a 5-6 fold increased risk of suicide. For perspective, this risk increase coincides with the risk of undergoing severe stress under deployment (seeing wounded, killed, or dead comrades, for example) and the risk of suicide.
We can't determine causality, but common sense and and evolutionary perspective should surely make us suspicious - eat those marine omega3s and keep your 6:3 ratio minimal. The paper recommends 2 grams daily of marine omega 3s.. Seems reasonable.