The supplement industry is a 122 billion dollar behemoth, and it’s growing. We can debate the scientific validity of supplements back and forth for hours, and days, but how much do we know about the basics?
As kids, Hulk Hogan told us to “take our vitamins.”
But what is a vitamin, anyway?
In a previous post, we took a look at the B vitamins in nutrition and health. But let’s take a step back for a more basic topic and actually look at what a vitamin is, and isn’t.
In order to be defined as a vitamin, a molecule must meet four criteria.
- A vitamin must be an organic compound, very simply this means it must contain at least one carbon atom.
- Vitamins must be vital to life, i.e. without it a person could not survive.
- Vitamins are required in limited amounts, this definition is the most woolly as there is no hard definition of limited.
- Finally, vitamins cannot be synthesized by a person in sufficient quantities, i.e. they must come from the diet.
Let’s look at a few common nutrients to see if they tick all the boxes.
What are vitamins?
Is iron a vitamin?
We’ll start with iron. Whilst it ticks the latter three points, iron falls at the first hurdle as it doesn’t contain a carbon atom. A compound containing both iron and carbon (such as iron carbonate) passes this check, but then fails on the vital to life aspect, as whilst iron is vital to life, iron carbonate is not.
Is glucose a vitamin?
OK, let’s pick something a bit more complex. Glucose is a simple carbohydrate, is definitely vital to life, and since it contains six carbon atoms it passes that point as well. But it falls down on the other two points, firstly because it can be synthesized in the body from the longer complex carbohydrates and fats that we eat, and secondly because it is required in large amounts to provide energy.
Vitamin C – the uniquely human vitamin
Let’s try one more example, ascorbic acid or Vitamin C, a very famous vitamin indeed. Containing six carbon atoms it passes the first point, it is defiantly vital to life as it plays a key role in tissue maintenance and repair. Indeed, diseases such as scurvy, characterized by breakdown of the bodies tissues, rapidly appear in the absence of ascorbic acid.
The exact amount required isn’t known but estimates range from 60-100 mg per day, with little to know benefit from exceeding this amount, so we can definitely say it’s required in limited amounts. Finally, ascorbic acid cannot be synthesized directly by humans, rather we must obtain it from food (citrus fruits and tomatoes are especially rich) or via supplements. It ticks all the boxes and so is classed as a vitamin. Interestingly, most plants and animals on the planet can synthesize ascorbic acid, whereas humans and a few other species can’t. So, whilst ascorbic acid is a vitamin for us, it isn’t for most other species.
You may have noted that above I said ascorbic acid was the most common form of vitamin C. This is important as vitamins are classified based on function, not exact structure. So for example sodium ascorbate is also classified as vitamin C.
The thirteen vitamins
There are currently thirteen recognized vitamins. Vitamin A, D, E and K (all fat soluble) and 8 types of B vitamins, plus vitamin C (all water soluble).
The functions of these vitamins is very diverse, for example vitamin C is important in tissue repair, whereas vitamin D, which we’ve written a good bit about lately, is important for regulating bone mineral metabolism.
So, there you have it, a simple set of criteria for determining what is, and what is not, a vitamin.
While it’s pretty easy to simply consult the list of thirteen recognized vitamins, it’s nice to know a little more about why a vitamin is called a vitamin, and why we supplement with the nutrients we do.