 In the landmark Global Burden of Disease study, they compiled the top 20 causes of death and disability. Number one, on the list, was high blood pressure, two and three are smoke. The number four leading cause of loss of life and health was not eating enough fruit. Lack of exercise was number 10, then too much sodium, then not enough nuts and seeds, not enough whole grains, not enough vegetables. Number 18 was not getting enough long chain omega-3 fatty acids, like EPA and DHA, found in seafood due to their purported protective effect against heart disease. Even years ago, when this was published, however, they were already questioning the benefits of these fish fats as more and more randomized controlled trials put them to the test and they failed, culminating in the recent meta-analysis that I profiled previously that appeared to put the issue to rest. Cardiovascular protection isn't the only thing fish and fish oil consumption was hyped for, though. Omega-3s have also been touted to treat depression, but after taking into account all the negative results that went unpublished, there appears to be no benefit for major depression or for preventing suicide, as I explored previously in my video on fish consumption and suicide, but what about for the prevention of cognitive decline or dementia? The available randomized controlled trials show no benefit for cognitive function, for omega-3 supplementation in studies lasting from 6 months to 40 months among healthy older adults. It may sometimes even make things worse. Higher current fish consumption predicted worse cognitive performance and greater past fish consumption in childhood predicted slowed perceptual speed and reaction time. This may be due to neurotoxic contaminants in fish, such as mercury. We've known that the developing brain is particularly sensitive to the damaging effects of mercury, but maybe the aging brain is as well. This would explain results like this, where higher omega-3 levels were associated with high levels of cognitive impairment and dementia. More EPA found in the cognitively impaired and more DHA found in the demented, presumably because of pollutants like mercury and PCBs in seafood that have been related to cognitive impairment or Alzheimer's disease. The same cognitive functions disrupted in adults, like attention, fine motor function, verbal memory, are similar to those previously reported in children exposed in the womb. And the adults exposed to mercury through fish consumption didn't just have like subtle EEG brainwave changes or something, but observable deficits in neurobehavioral performance measures. For example, poorer performance on tests of fine motor speed and dexterity, concentration, some aspects of verbal learning and memory were also disrupted by mercury exposure, and the greater the mercury levels, the worse they did. But look, this study was done downstream of a gold mining operation, a process that uses lots of mercury. Other such studies were done on people eating fish next to chemical plants or toxic spills or eating whale meat. What about a more mainstream population? In fact, an elite group of well-educated participants, really well-educated, most were corporate executives like CEOs, all living in Florida, and wealthy enough to afford so much seafood that at least 43% exceeded the EPA safety limit for mercury, and it had an effect. Excessive seafood intake, which they defined as like more than three or four servings per month of fish like tuna or snapper, elevates mercury levels and causes cognitive dysfunction. Not much, only about a 5% drop in cognitive performance, but a decrement that no one, let alone a health-conscious and achievement-oriented person, is likely to welcome. It's worth noting the irony of this situation, the fact that corporate executives who chose to over-consume seafood for health reasons instead sustained a drop in their executive functions as a result. Yet if a 4.8% drop in executive function due to excessive seafood intake occurs in highly functioning healthy adults with ample cognitive reserve, the major concern is whether similar mercury-level elevations in individuals already suffering from cognitive decline might result in substantially greater declines, particularly with cognitive decline dementia and seafood consumption on the rise.