Transcript: Fish Consumption and Suicide
Depression is a serious and common mental disorder responsible for the majority of suicides, but as I already covered, intake of fruits, vegetables, and naturally occurring antioxidants have been found to be protectively associated with depression. So, they concluded, it may be possible to prevent depression or to lessen its negative effects through dietary intervention.
But not so fast. This was a cross-sectional study, meaning a snapshot in time; so, you don’t know whether the poor dietary pattern precedes the development of depression or if depression causes poor dietary intake. Depression and even treatments for depression can affect appetite and dietary intake. Maybe people who feel crappier, just eat crappier, instead of the other way around. What you need is a prospective study, a study performed over time, where you start out with people who are not depressed and follow them for 6 years, and those with higher carotenoid levels in their bloodstream, which is considered a good indicator of fruit and vegetable intake, had a 28% lower risk of becoming depressed within that time. So, the researchers conclude that having low blood levels of those healthy phytonutrients may predict the development of new depressive symptoms, but what about suicide?
Worldwide, a million people kill themselves every year. In this comparison of European countries, Greece had the lowest rates of suicide. Maybe it’s the balmy weather, but maybe it has something to do with their diet. 10,000 people followed for years, and those following a more Mediterranean diet pattern were less likely to be diagnosed with depression. What was it about the diet that was protective? It wasn’t the red wine, or fish; it was the fruit and nuts and effectively higher plant to animal fat ratio and beans that appeared protective. Conversely, significant adverse trends were observed for dairy and meat consumption.
A similar protective dietary pattern was found in Japan; a high intake of vegetables, fruit, mushrooms and soy products was associated with a decreased prevalence of depressive symptoms. It was not characterized by a high intake of seafood. 100,000 Japanese men and women were followed for up to 10 years, and they didn’t find evidence of a protective role of higher fish consumption or the long chain omega 3’s EPA and DHA against suicide. In fact, they found a significantly increased risk of suicide among male nondrinkers with high seafood omega 3 intake. This may have just been by chance, but a similar result was found in the Mediterranean. High baseline fish consumption together with an increase in consumption were associated with an increased risk of mental disorders.
One possible explanation could be the mercury content of fish. An accumulation of mercury compounds could increase the risk of depression. We know that mercury in fish can cause neurological damage, such as negative effects on Alzheimer disease, memory loss, and autism as well as depression.
So, the increased risk of suicide among persons with a high fish intake might be attributable to the harmful effects of mercury in fish.
The big Harvard cohorts found similar results; hundreds of thousands followed for up to 20 years, and no evidence that taking fish oil or eating fish lowered risk of suicide, with a trend towards even higher suicide mortality.
What about for the treatment of depression? Neither EPA nor DHA appeared more effective than sugar pills, and the same can be said when one puts all the trials done to date together. We used to think omega-3 supplementation was useful, but several recent studies have tipped the balance the other way. It seems that nearly all of the treatment efficacy observed in the published literature may be attributable to publication bias, meaning the trials that showed no benefit tended not to get published at all, and so all one saw was a bunch of positive studies, but only because a bunch of the negative ones were buried.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
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