A blood test can be done to check vitamin D3 levels. 30 to 50 ng/ml (70 – 125 nmol/L) is the normal range. Less than 15 ng/ml (38 nmol/L) is far too low, and over 100 ng/ml (250 nmol/L) constitutes hypervitaminosis which is also dangerous.

Most commercially available vitamin D3 is not vegan since it is usually made from lanolin fat from sheep’s wool. Vegan vitamin D2 is made from vegan sources like yeast and mushrooms and has been available but there is some debate on the virtues of D2 over D3. Many say vitamin D3 is more easily used than vitamin D2. Luckily now vegan vitamin D3 is available too.

Supplementation can be oral or by injection. If the values are very low, injections may be best.