A large just-published study found that giving people who already have Alzheimer’s 2 g/day of DHA (present in fish oil) did not reduce their cognitive decline compared to placebo (corn or soy oil). Fish consumption had been found many times to be associated with a reduced risk of Alzheimer’s.
Thanks to Saul Sternberg.
There is a difference between slowing the course of existing Alzheimer’s disease (the subject of this study) and reducing the risk of the disease for the currently unaffected – a question not addressed in this research.
Jeremy, there are lots of nutritional disorders where something that prevents the problem also slows or reverses its course. For example, Vitamin C prevents and cures scurvy. Here is another example (thanks to Anne Weiss). I can’t think of any cases where something that prevents a disease does NOT slow down the disease once it starts.