Vitamins are an important part of our diet, but you probably haven’t given a great deal of thought to their chemical structures. This graphic shows chemical structures for all 13 vitamins; though there can be some variability in these structures in sources of the vitamins, these are generally representative. They perform a range of roles in the body; below is a brief discussion, and a look at the evidence for taking vitamin supplements.

First, it’s worth discussing what makes a chemical compound a vitamin. A vitamin is defined as any organic compound that a living organism requires, but which it is not capable of producing itself, or cannot produce in the amounts required by the body. As far as the definition for vitamins goes, this doesn’t include the other essential nutrients that are found in our diet, such as amino acids, fatty acids, carbohydrates and minerals.

Currently, there are 13 recognised vitamins: vitamins A to E, including a range of B vitamins, and vitamin K. The slightly odd gap in lettering between E and K is a consequence of changes in designations of vitamins; for example, vitamin B7, biotin, was previously referred to as vitamin H. The compounds originally designated as vitamins F to J were either redesignated, or subsequent research led to them no longer being classified as vitamins.

Generally, we can stick all of the vitamins into two broad categories. The fat soluble vitamins, vitamins A, D E, and K, can be stored by our bodies in the liver or in fatty tissues. They are stored until they’re required, which consequently means they generally don’t need to be ingested as frequently. Water soluble vitamins, on the other hand, are not stored in the body. As such, they must be a regular part of the diet in order to avoid deficiency. Conversely, the fact that water soluble vitamins aren’t stored in the body makes it harder to overdose on them, which can also have detrimental effects.

Some vitamins are chemically simpler than others; vitamin D, for example, occurs naturally only in the form shown in the graphic. Others, such as vitamin E, can come in the form of a range of structurally similar compounds, with the exact substituents varying. The active form of vitamins in the tissues of mammals can also be marginally altered from the manner in which it occurs in foods.

Vitamins have a wide range of roles within the body, a brief summary of which is given in the graphic above. For example, a number of the B vitamins are important for making red blood cells, and metabolism of a variety of compounds during digestion. Others have uses in more specific parts of the body; for example, vitamin A is important for our eyesight, whilst vitamin K plays a major role in the clotting of blood. Similarly, deficiencies of vitamins can also have effects; a lack of vitamin C can lead to scurvy, the bane of sailors before the role of vitamin C was understood. A lack of vitamin K can cause bleeding problems, which is why newborn babies are given a shot containing the vitamin, preventing bleeding on the brain and the subsequent potential brain damage.

So, should you take vitamin supplements to avoid these deficiencies? If you have a balanced diet, then chances are you’re already getting these vitamins in the required quantities. There are cases where supplements are recommended for those who are at risk of deficiency; however, for the general population, the evidence for taking them might be a little shaky. A review of studies involving a sum total of 400,000 people taking vitamin supplements found that they did little to prevent chronic disease or death, and concluding that if multivitamin supplements have any effect, then it is a very small one.

If you want find out much more about the sources and roles of the various vitamins, check out the links provided below.

The graphic in this article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

References & Further Reading

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