Every cell in your body needs vitamin A. This nutrient regulates the growth and division of your cells and it helps your body produce white blood cells when you need to fight an illness or infection. It plays a role in remodeling bone and it keeps the cells that line your body's interior surfaces healthy. Smokers should avoid high-dose supplements of beta-carotene, according to Harvard School of Public Health, because it may increase their risk of lung cancer, but getting the recommended amount through food is healthy and safe.