Vitamin deficiency could cause cognitive problem
Your eating may not have changed however based on a Harvard eating medical study which lasted 25 years, showed that those who eat large amounts of vegetables over years and less red meats and dairy, rarely have age related decline in memory (Today Health.com).
What you could do to reverse this deficiency.
You should eat more leafy green vegetable dishes, broccoli, kale, spinach and leeks. The Harvard study shows that eating more foods with anthocyanin and quercetin actually changed the age related memory deficit in the tested animals. This information is from Today Health.com.