As reported in NutraIngredients, a study found that eating fish at least once a week may help slow down onset of dementia. The full study article is available on JAMA Neurology (formerly Archive of Neurology) linked here.
It concluded that “Fish consumption may be associated with slower cognitive decline with age” but did not know whether it was the omega-3 oil in the fish or not. Perhaps the measurement of DHA and EPA was too imprecise to make a significant association. However, the authors did comment that …
“We hypothesized that DHA would have the strongest association with cognitive change based on its abundance in brain tissue and evidence from animal models demonstrating superior learning and memory performance among DHA-fed rodents. The absence of association with DHA raises the possibility that the observed fish association was due to some other dietary constituent or perhaps to another factor that is related to cognitive health and fish consumption.”
FoodForTheBrain.org says that getting enough B vitamins to reduce homocysteine is important but that …
“Other nutritional solutions which research suggest can affect cognitive decline or Alzheimer’s risk include omega 3s (DHA), antioxidants such as Vitamin E (due to the inflammatory nature of AD) and acetylcholine which is a key part of memory function (which is often deficient in Alzheimer’s cases).”
Personally, I believe that the mechanism of action in delaying the onset of dementia is the DHA and that it is better to get it in the fish rather than from supplements, since the meat of the fish protects the oils even when steaming the fish. The oils in supplement form is easily oxidized due to the fragility of polyunsaturated oils. If you are using supplements, get the liquid form and keep in refrigerator.
What about the Mercury in Fish?
There is always a question of mercury in fish. While it is true that nearly all seafood is contaminated with mercury to a certain extent. The general rule that the smaller the fish, the lower the mercury. Since the large fish eats the small fishes and bio accumulates more mercury. I would stick with salmon and sardines and avoid large fishes such as tuna and certain sea bass.
Also it has been argued that the selenium in fish help with the detoxification of mercury. Chris Kresser article says that eating fish is safer than not eating fish. His podcast linked here talks about this in greater detail with guest Dr. Nicholas Ralston.