Well, this is wonderful news! Says physically active me with severe insulin resistance hyperglycemia and a mother with fast declining cognitive function and dementia. Cause to be optimistic about the health of my brain in the years to come.
Alas, my poor demented mother is one of the most physically active people I know. She is so fit it's almost ridiculous. She went on a three day hike for her 80th birthday, including a spot of kayaking for good measure. (We live in NZ, so hey!) But, she eats a lot of processed food (modern food of choice for the elderly without ovens), and high-sugar food. Probably low protein but am not as sure of that. I have not been able to talk her out of that, and I have tried.
IMHO, it is physical activity in combo with lowering the grains and carbs in your food which would really help prevent or stay the course of dementia.
More so the food and drink than the activity. (Just like diabetes?!) IMHO.