Also important are trace minerals including copper, manganese, selenium, and zinc, which are essential for antioxidant-enzyme function. Each act in different parts of the cell. For example, vitamin E acts in cell membranes, while vitamin C acts in the cell body itself, the cytosol. To effectively protect neurons in the brain, antioxidants must penetrate the blood-brain barrier and reach a sufficiently high concentration in brain tissues. It is almost totally impermeable to large, nonlipid-soluble molecules and to plasma proteins.
Vitamins cross the blood-brain barrier but reach different areas with different efficiencies.
Because free radicals have been implicated in PD, antioxidants should, in principle, reduce the risk of neuron degeneration and dopamine oxidation. In vitro studies support the theory that vitamins C and E suppress oxidative destruction of dopamine. Results, however, are inconsistent. Lifestyle factors could contribute to the inconsistency because lifestyle may play a role in PD that cannot be accounted for. At least one compelling case has been made for vitamin E's protective effect against PD, and that's when it was consumed long-term starting in early adult years.