Vitamin D is a very important vitamin. It is formed mainly in the skin and then used by every cell in the body.
Correct levels of vitamin D are important for the immune system to work properly.
Ninety per cent of vitamin D is made from sunlight exposure directly on to the skin (not through glass).
Only about 10 per cent of vitamin D comes from food sources such as oily fish, fortified milk and egg yolks.
Your doctor can order a blood test.
This often makes it hard to get enough sun to make vitamin D. It is therefore recommended that you take extra vitamin D in the form of a supplement; this will benefit both you and your baby.
People who are vitamin D deficient are at risk of having softer bones that are prone to breaking. Muscles can be weak and sore in severe deficiency.
Children with very low vitamin D levels can develop rickets. This can be serious. Because the bones don’t form normally the child can be short and the legs bowed. Sometimes the calcium level in the blood can be very low and this can lead to the child having seizures (fits).
from WA dept of Health