MARSHALL BRAIN, HowStuffWorks.com | Posted: Monday, October 29, 2007 12:00 am
Humans need certain vitamins to survive. But what, exactly, is a vitamin? Why do you need vitamin C or A or B every day?
A vitamin is a small molecule your body must have to carry out a certain chemical reaction. In some cases your body has no way to create vitamin molecules itself. In other cases, your body has a way to make a vitamin molecule, but may not make enough. When your body does not make a vitamin, or does not make enough of a vitamin, the vitamin molecules must come in through the food you eat. The human body is known to need at least 13 different vitamin molecules.
For example, your body needs vitamin C, also known as ascorbic acid. It is a very simple molecule containing six carbon atoms, eight hydrogen atoms and six oxygen atoms. Your body needs this molecule for several reasons, but most importantly because of collagen. When your body produces collagen, it performs a chain of chemical reactions. The vitamin C molecule is an essential part of the chain. Since collagen is used in everything from skin to blood vessels, you can see how important vitamin C is. Without it your blood vessels weaken, your teeth start to fall out and you eventually fall apart and die from a lack of collagen. All because of one missing molecule.
Vitamin D is another important simple molecule. We actually have the ability to produce vitamin D in our skin, but to do it we have to have regular exposure to the sun's ultraviolet rays. Without enough sun exposure people get different ailments depending on their age. In children, a lack of the vitamin D molecule causes rickets, which softens the bones and causes them to deform or break easily.
Why do we need to "take" these molecules? While the human body is equipped to create its own vitamin D, our lifestyles have changed. Ages ago, people lived outdoors and got sun exposure every day. Modern humans often spend days at a time indoors, especially in winter, with little or no sun exposure. To prevent rickets we add vitamin D to milk and other foods just in case a child isn't getting enough naturally.
The case of vitamin C is even more interesting. Dogs have no need for citrus fruits. They, like most animals, produce their own vitamin C molecules inside their bodies. Human beings, like many other ape species, lost this ability because of genetic damage that occurred somewhere in the evolutionary chain. Apparently, at some point during the evolutionary process, the vitamin C gene was damaged. We inherited this damaged gene. Because of this humans must get vitamin C from food.