It can be easy to think you get plenty of vitamin D when you live in a country bathed in sunshine, but the reality is more complicated.

Almost one in four Australian adults have vitamin D deficiency. Vitamin D supplements are now one of the most commonly used complementary medicines.

So what is vitamin D? And do you need to take it as a supplement?

It functions like a hormone

Vitamin D is a fat-soluble vitamin that plays a crucial role in maintaining overall health. Unlike most vitamins, it functions more like a hormone in the body, and nearly every cell has a receptor for it.

It exists in several forms, but vitamin D3, also known as cholecalciferol, is the most important. Once in the body, D3 undergoes changes – first in the liver and then in the kidneys – to become its fully active form called calcitriol.

Your body is capable of producing its own vitamin D by converting a cholesterol precursor into it, but that requires exposure to ultraviolet radiation (UVB) on your skin.

You can also get it through diet from a few foods including eggs, oily fish and mushrooms – but it’s unlikely to be as much as you need.

What happens when you don’t get enough vitamin D?

Vitamin D’s best-known role is helping the body use calcium. It promotes the absorption of calcium from the gut, ensuring an adequate level in the blood for building strong........

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