Also called thiamine, vitamin B-1 converts glucose to energy. It is essential for normal functioning of the heart, brain, nervous system and muscles. 

How Much: Recommended dietary allowance (RDA) = 1.2 mg for men; 1.1 mg for women.

Too Much: No known symptoms.

Too Little: Deficiency can cause weakness, fatigue, psychosis and nerve damage. 

Foods: Vitamin B-1 in the form of thiamine is found in whole grains, brown rice, pork fish and dried beans; also in enriched pasta, bread, cereals and rice. 

Interactions: Furosemide (Lasix); antacids; Digoxin; Phenytoin (Dilantin).

Research Note: Small studies have suggested vitamin B-1 might be important for people who have heart failure and in preventing cataracts – both associated with rheumatoid arthritis (RA).