Because disease is caused by vitamin deficiency, supplements can prevent these conditions. Just as an example, a deficiency in Vitamin A can cause cells to abnormally develop in the esophagus and mouth. But, people who are at risk for developing oral cancers, like those who smoke and drink, cannot necessarily prevent these cancers by taking supplements of Vitamin A. Or, people with deficiencies in Vitamin B12 are at a higher risk for developing stomach cancer, but may not be able to properly absorb the B12 vitamins due to problems with the gut.

Deficiency is indicated by having low levels of certain vitamins. When a person follows a balanced diet, a true vitamin deficiency is very unlikely. Many people take a Vitamin D supplement, because their bloodwork shows low levels, but it is unclear whether or not blood levels can accurately measure how much Vitamin D is stored in the body. A typical healthy diet and adequate sun exposure can usually provide plenty of Vitamin D to the average person.

People assume that vitamins are safe because they are not medicines. This is one of the more dangerous myths surrounding vitamin supplementation. Too much of a good thing can lead to serious problems. Vitamin overdosing is not uncommon. Although vitamins in recommended doses are generally considered to be safe, caution must be used when “superdoses” are recommended.

Vitamin toxicity, especially with Vitamin A, can be very dangerous. This toxicity is especially dangerous in children, because there is a possibility that bones can grow abnormally, the brain can swell and liver damage can occur. Certain vitamins may be more likely to cause toxicity, particularly the fat-soluble vitamins of A, D and K, which are stored in the body and difficult to excrete. Water soluble vitamins, like Vitamin C, are less likely to cause toxicity because they are easier to excrete and cause less stress on the kidney and liver.

Vitamins are “all-natural”. Just because something is all-natural doesn’t mean it is good for you. Vitamins are often considered to be natural because they are not specifically drugs or medicines, but they are derived through chemical synthesis processes, much like the way drugs are produced. Certain drugs, such as penicillin, was initially created from a natural fungus and chemically derived, but considered to be one of the safest drugs available—with the exception of the allergic reaction for some people.