Zinc is included in most single tablet over-the-counter daily vitamin and mineral supplements. Preparations include zinc oxide, zinc acetate, and zinc gluconate. It is believed to possess antioxidant properties, which may protect against accelerated aging of the skin and muscles of the body; studies differ as to its effectiveness. Zinc also helps speed up the healing process after an injury. It is also suspected of being beneficial to the body's immune system. Indeed, zinc deficiency may have effects on virtually all parts of the human immune system.