Vitamin B-9 Reduces Dementia by 3x

It seems that folate which is in leafy vegetables such as spinach, turnip greens, lettuces, dried beans and peas and in certain fruits reduces the risk of dementia by 3 to 1.

An study published last year in The Lancet showed an improvement in
short-term memory, mental agility and verbal fluency among persons over 50 who took a daily dose of 800 micrograms (mcg) of folic acid. The US recommended daily dose is 400 mcg.

This vitamin seems to make new cells so I guess it stops the brain from not creating new cells to replace the ones that are lost to aging.