He said the tensions over Tamerlan's strict adherence to religion, along with his own health problems, weighed on him and his marriage.

WSJ: Boston Marathon Bombings: Turn to Religion Split Bomb Suspects Tamerlan and Dzhokhar Tsarnaev's Home

For example, other research has found that higher adherence to the diet seems to protect against hypertension, also associated with these brain problems.

CNN: Mediterranean diet may help prevent dementia, study says