One of the reasons why curcumin helps dementia patients is that it is able to bind with the VITAMIN D RECEPTOR.
So people who regularly consume curcumin are in fact compensating for their vitamin D deficiency by providing an alternative.
Average dietary intake of turmeric in the Indian population may range between 2 to 2.5 grams, corresponding to 60 to 200 milligrams of curcumin daily. It may be the reason when people from India/Pakistan immigrate into the UK they don't suffer quite as much from the lack if vitamin d moving further from the equator inevitably means because those who maintain their traditional diet, with it's reliance on Turmeric, are to some extent protected from the effects of vitamin D deficiency.
Both vitamin D and curcumin help the brain clear Amyloid Beta.
In fact they work better together than separately
1alpha,25-dihydroxyvitamin D3 interacts with curcuminoids to stimulate amyloid-beta clearance by macrophages of Alzheimer's disease patients.