Folic acid deficiency could increase the risk for Parkinson disease, according to research from the National Institute on Aging (NIA). In the study, mice fed folate-deficient diets developed severe Parkinsonlike symptoms, which the scientists traced to elevated levels of homocysteine in the brain. They suspect that this excess amino acid damages DNA in the substantia nigra, a brain structure rich with dopamine cells. In mice fed adequate amounts of folic acid, however, dopamine neurons repaired intentionally damaged DNA, counteracting the effects of excess homocysteine.
Vastag B. Folic Acid and Parkinson Disease. JAMA. 2002;287(7):832. doi:10.1001/jama.287.7.832-JHA20002-2-1