Vitamin B group is needed for the conversion of glucose into brain energy and good functioning of the body immune system and mental health. Even a mild deficiency can cause you to become irritable, lack of concentration and forgetful. Foods that help include mushrooms and cauliflower.
Type II diabetes and depression are co morbid, which means they happen together more than expected based on the rates of each disease alone. The question among scientists is whether one disease can cause the other or whether there are factors that lead to both at the same time.