Ginko Biloba's purported effects to be overblown, another study has looked at fish oil supplements and found that they were neither effective in boosting brain power nor in preventing cognitive decline. Here's a summary at Brain Blogs:
While I am always skeptical of the real power of nutritional supplements (usually because rigorous study finds them minimally effective at best, or because scientific studies that do show promise are almost always epidemiological or in vitro, the former being limited by an inability to control for numerous other factors, and the latter being limited by the stark differences between the environment in a dish and that inside the body), this isn't a "nail in the coffin" in terms of fully debunking the potential of fish oil, but it is a strong case for not forcing your grandparents to choke down cod liver oil in hopes that it will stave off dementia.
That being said, I am out of town at the moment, and not really able to read up on other studies on the purported benefits of fish oil supplements. So, it may be true that fish oil still has some cardiovascular benefits. Or, since olive oil was used as the control supplement in this study, it may be that it, or any other unsaturated fat is just as good for protecting the brain from decline, and perhaps a better control would be to compare unsaturated fats (like olive oil and fish oil) to saturated fats (like butter and bacon fat). Also, since the background for this type of study is epidemiological, it may mean that fish oil needs to be taken throughout life, rather than just for 2 years during old age (though that's a pretty long time to not see an effect). However, fish oil may be beneficial in people who are more susceptible to cognitive decline (or already experiencing symptoms of dementia). Since this study tested healthy adults, and none of them experienced cognitive decline, we can't say it has absolutely no effect, just that it has no effect in healthy individuals.
So, while I will try to do some more research when I get home, and see if fish oil really does anything, the one thing I can say for sure is, if you are healthy and in your 70s, fish oil isn't going to help you any more than olive oil, and I don't know if either is going to help you that much (at least not as a supplement).
Thanks to Bill Nelson for giving me the heads-up on this study.