In PD it was thought to delay progression but after a careful study it does not look like this is true. It most likely does not get across the blood brain barrier. It is still good for other disease processes such as heart disease, perhaps cancer, and others. I should first start with vitamins in general. A well balanced multivitamin is important in normal aging and any chronic illness.
Good nutrition can be harder to come by and a good vitamin is protective for nutritional deficits.
The other supplement is calcium. A glass of milk has 300mg so you can start to estimate how much you get in food. It is a powerful antioxidant, boosts energy, and the immune system. There is a controlled double blind clinical trial being done right now to answer this question. It can be found in any health food store.