These nutrient deficiencies can also cause mood disturbances, confusion, poor concentration, easy agitation and nerve-cell damage that make extremities numb, according to Lona Sandon, of the University of Texas Southwestern Medical Center, in Dallas.

"If you're deficient, improved dietary intake can improve alertness and concentration when normal blood levels are reached," Sandon said in a statement.

Sandon lists the nutrients that are good for the brain followed by foods rich in that nutrient:

-- Iron: Beef, fish, poultry, leafy vegetables

-- Zinc: Oysters, nuts, grains, beans, cereals, whole-grain breads

-- Niacin: Beef, fish, poultry, leafy vegetables, nuts, grains, tomatoes,carrots, milk

-- Thiamin: Beef, pork, nuts, grains, peas, spinach, some beans, breads

-- Vitamin B6: Liver, fish, poultry, green beans, bananas, nuts

-- Vitamin B12: Beef, liver, shellfish, eggs, milk, fortified cereals

-- Omega-3 fatty acids: found primarily in fish