Oysters are very low in calories, and provide a good source of Vitamins D & B12, as well as Iron, Copper, Manganese and Zinc. These nutrients are associated with the prevention or slowing of of osteoporosis especially in older women. Additionally, Vitamin B12 has been linked to good brain health, which can help against dementia and Alzheimer's disease, both of which are associated with a deficiency in Vitamin B12. Oysters are also a good source of selenium, which the body needs in small quantities.