Natures Aid Vitamin D 10ug is important in helping the body absorb & use calcium from food & supplements. It aids in bone & tooth formation & supports muscle & nerve function & studies have shown that vitamin D helps to prevent osteoporosis. Nutritionists categorise vitamins by the materials that a vitamin will dissolve in. There are two categories: water-soluble & fat-soluble vitamins. Fat-soluble vitamins A, D, E & K are stored in the fat tissues of the body for a few days to up to six months. If you get too much of a fat-soluble vitamin, it can be stored in your liver & may sometimes cause health problems. Vitamin D is a fat-soluble vitamin. Some people take mega-doses of fat-soluble vitamins, which can lead to toxicity. Eating a normal diet of foods rich in these vitamins won't cause a problem. Remember, you only need small amounts of any vitamin. Some health problems can make it hard for a person's body to absorb these vitamins. If you have a chronic health condition, ask your doctor about whether your vitamin absorption will be affected.