To answer this question properly, we need to understand that Vitamin D is a type of vitamin, rather than the vitamin itself.
Vitamin D is used when we talk about Vitamins D3 and D2, which are slightly different from one another.
The main difference between the two is that Vitamin D2 comes from plant sources and Vitamin D3 comes from animal sources (e.g. cod liver oil, egg yolks).
Vitamin D3 is also created in your body when sunlight hits your skin, which is why the NHS advises Brits to take vitamin D supplements during the winter months.
If you buy Vitamin D or a multivitamin with Vitamin D included, the nutritional table on its packaging will let you know whether you’re getting Vitamin D2 or D3, so if you need one, in particular, this is where you’ll find the information you need.