What is vitamin D?

Vitamin D is a fat-soluble vitamin with an important role in aiding the absorption of calcium, magnesium and phosphates. It also contributes to bone and musculoskeletal health. Vitamin D is acquired by the body in two different ways; dietary vitamin D is consumed in food and supplements and is in the form of vitamin D2 from plant sources and D3 from animal sources. Vitamin D3 is also produced by the skin in response to exposure to sunlight, which is the primary source of vitamin D for the body, making up around 80-90% of the total vitamin D. In the UK, the sun is only powerful enough to stimulate vitamin D production in the skin between around April and September. Due to the fact that this is the primary source of vitamin D in the body, it is common for vitamin D deficiency to occur in many parts of the UK during the winter months without supplements. Vitamin D deficiency can result in weakness in bones and muscles and has been associated with asthma in children and cognitive impairment in adults. Excess vitamin D through supplementation can lead to hypercalcemia.

Why take the test?

This test measures the levels of vitamin D in the blood. It is typically used to investigate vitamin D deficiency or excessive supplementation. Vitamin D deficiency can be the result of insufficient intake and production or problems absorbing the vitamin.