Vitamins are essential nutrients, which means that they are needed by the body, but not produced in the body. As a result, people need to get vitamins in food or from other sources in order to get enough. There are 13 vitamins, though some chemicals that were formerly included among the B vitamins were later determined to be a different type of nutrient, which is why the B vitamins skip B4, B8, B10,and B11. The current list consists of vitamin A, 8 types of B vitamins, C through E, and vitamin K. A, D, E, and K are stored in the body’s fat cells; the remainder are water-soluble and get passed in urine, meaning they are needed more frequently.
Doctors have long—as far back as ancient Egypt—recognized that certain foods treated certain ailments, but before the development of organic chemistry they were at a loss to explain why. For example, in 1747, a Scottish doctor discovered that citrus prevented and treated a disease called scurvy, what we now know as vitamin C deficiency. In 1881, a Russian surgeon found that experimental animals fed an artificial milk made out of the known proteins, fats, salts, and sugars, in the right proportions, died, whereas animals fed milk thrived; he concluded that there was some other, unknown nutrient. In the 20th century, these nutrients were chemically isolated and named vitamins.
Thanks to an improved understanding of vitamins, and nutrition in general, vitamin-deficiency diseases, such as rickets, scurvy, and beriberi, are virtually unknown in the developed world today. However, the mindset that if something is god, more is better has led to a market for vitamin supplements. While some people have medical conditions that interfere with vitamin absorption, most people in the West get sufficient amounts of most vitamins from their diets, and vitamin pills do little more for those people than give them costly and sometimes colorful urine.
However, it is possible to overdose on vitamins. This is particularly true of vitamins A, D, E, and K, which don’t get flushed out in urine, but all vitamins can be harmful if taken in excess, and in some cases this can cause permanent damage.