A stroke occurs when part of the brain is damaged from lack of normal blood supply. This may result in difficulty with feeling, speech, muscle strength or coordination, movement, thinking, or other brain functions. Having a stroke increases the risk of another stroke occurring in the future. Higher blood levels of a natural chemical known as homocysteine may contribute to hardening of the arteries in the brain or heart and increase the risk of stroke or heart attack. Folic acid, vitamin B6 (pyridoxine), and vitamin B12 (cyanocobalamin) may lower blood levels of homocysteine and reduce the risk of having another stroke or a heart attack.