The author hypothesizes that turmeric helps prevent Alzheimer’s disease. Why? First, because of a correlation: people in India eat lots of turmeric, and very few get Alzheimer’s disease. Second, because of turmeric’s effect on the brain: the curcumin it contains reduces the buildup of amyloid proteins that characterize Alzheimer’s disease, at least in animals.

The author assumes eating turmeric makes more curcumin available for breaking down amyloid proteins in the brain, thus reducing the risk of Alzheimer’s disease. This means assuming curcumin has the same effect on amyloid proteins in humans that it does in animals. She also assumes the correlation in India—more people eat turmeric and fewer get Alzheimer’s disease—is because turmeric consumption reduces a person’s chances of Alzheimer’s disease, and not for some other reason.