Vitamin D

What it is

Most vitamin D is made by your skin when it’s exposed to UV light from the sun. Smaller amounts come from food. Your liver and kidneys convert it into forms the body uses. The blood test measures 25-hydroxy-vitamin D, the form that reflects how much is available.

Why it matters for training decisions

Vitamin D’s best-known job is regulating calcium and supporting bone health. A 2018 review of vitamin D in athletes notes that it may also play a role in muscle recovery and immune function. However, studies in athletes haven’t consistently shown the same link with bone health seen in non-athletes, possibly because exercise itself strengthens bone.

The same review warns that many athletes take vitamin D supplements, sometimes in very high doses, and that more isn’t automatically better. It also suggests that screening people with no symptoms or risk factors may lead to unnecessary supplementation.

Limits of the test

healthdirect notes that the “normal range” for vitamin D in the general population isn’t fully defined, and different laboratories may use different ranges. In Australia, most people get enough vitamin D through sun exposure, but people who are mostly indoors or covered up, or who have darker skin, may need more sun exposure to make enough. How much sun you need also depends on the season, where you live and the time of day. Balance this against skin cancer risk, and talk to your doctor before testing or supplementing.

How P247 uses it

If you turn on AI features, you can scan a blood test. P247 reads vitamin D and its reference range, tracks it across tests and adds a plain-English summary for training. It isn’t a diagnosis.

This glossary is general information to help you understand your training data. It isn't medical advice, diagnosis or treatment. For injury, illness, medication, blood test results or any health concern, speak to a qualified health professional.

← Back to the glossary