Most people know that vitamins are necessary for good health. However, the reasons for this necessity aren't always so clear. Here are a few of the reasons it's good to make sure vitamin intake is sufficient. Vitamins are nutrients that cannot be produced by the body. This sets them apart from other nutrients, like certain amino acids, that the body can make on its own. They are also in a different category than minerals. Since every species has a different set of substances it can make, what counts as a vitamin for one type of creature may not fall into that category for another. Thirteen substances are currently recognized as vitamins in humans. The reason nutrients like vitamins are required for health is that they are used in various biochemical processes. Deficiencies will slow or shut down the system the particular nutrient is needed for. Disease results when a deficiency becomes extreme. Many nutrients are just as necessary as vitamins for human functioning. These other substances, however, can be made by the human body and therefore do not qualify as vitamins. It is possible to become deficient in non-vitamin nutrients. This results from a variety of causes. Disease states can prevent the body from being able to complete the process of nutrient creation, malnutrition can deprive a person of the necessary building blocks or age can cause a slowdown of the necessary processes. Vitamin deficiency is usually unrelated to disease since the body doesn't produce these nutrients anyway. Instead, malnutrition is the most common cause. Even with a calorie-rich diet, people can suffer great deficiencies of necessary nutrients. It is quite possible to suffer from obesity and malnutrition at the same time. For these reasons, taking vitamin supplements is commonly recommended. A good multivitamin will ensure that you do not become deficient in essential vitamins. Some supplements also include minerals or amino acids to help cover deficits in these other vital substances. It can be a bad idea to take megadoses of vitamins and other supplements. This is because some nutrients are toxic in extreme amounts. For a person who is in generally good health, a standard dose multivitamin and mineral supplement is all that's needed to protect from deficiency.