Vitamin D is a very potent vitamin which the body only can produce in direct exposure of sunlight and is stored in the fat of the body.
It also exist in a small range of foods.
The problem is when you don't get any exposure of sunlight and you don't eat any food which contain vitamin D.
Vitamin D deficiency has been seen to result in a wide range of consequences such as Osteomalacia, Rickets, multiple sclerosis, rheumatoid arthritis, juvenile diabetes, Parkinson's, Alzheimer's disease, depression and low immune defence.
http://en.wikipedia.org/wiki/Vitamin_D
As you all know old people mostly cover up their body to not get cold, which in result leads to very little sun exposure.
I am not saying it is an universal cure, but I wonder if it can have a connection??