Your body needs 13 essential vitamins that you can get from eating a variety of foods. Because these vitamins each have a different role in the body, vitamin deficiencies can have a number of health effects, depending on which vitamin (or vitamins) you are lacking.
You can develop a deficiency due to low vitamin intake, and several medical conditions can predispose you to vitamin deficiency. Vitamin deficiencies can be detected with blood tests. And they can be corrected with oral (by mouth) or injected vitamin supplements.