All "research" that claims a low incidence of Alzheimer's in India is ERRONEOUS! Especially, it is amusing when westerners make this claim based on whatever "research" they managed to do. Let me clarify a few facts about India:
1) Majority of the doctors (not to mention the layman) in India are woefully unaware of Alzheimer's. Only in the last decade has awareness been introduced through campaigning.
2) Statistics in India about Alzheimer's is very skewed because of non-diagnosis and mis-diagnosis. Not surprising if even doctors are unaware of this ailment.
3) Longevity in India is around 60 years for men and 65 years for women. Put simply, they don't live long enough to get dementia or Alzheimer's.
4) In India, parents live with their sons as a rule. So, even the real Alzheimer cases are "kept under wraps" by the family and not really admitted to a nursing care facility. It would be tantamount to "abandoning" your parents or "exposing" their dementia to the world. Just not the Indian culture.
I am currently caring for my mother who is diagnosed with Alzheimer's after I brought her with me to the US. Prior to that, my father and relatives were complaining that she is acting crazy and is really difficult to get along with. But nobody even thought of it as a possible mental condition, they just attributed it to her "evil" nature. Sounds horrible, but that is the sad truth in India. Mental illness is often brushed off or ridiculed as if it is a personality trait. That is also why India is not very advanced in Psychiatry. Not because Indians don't magically have depression or other psychiatric issues. It is just that the society is not tuned in that well to these ailments.