Vitamin D Blood Test

What is vitamin D?

Vitamin D helps your body absorb calcium and maintain strong bones throughout your entire life. Your body produces vitamin D when the sun’s UV rays contact your skin. Other good sources of the vitamin include fish, eggs, and fortified dairy products. It is also available as a dietary supplement.

Vitamin D must go through several processes in your body before your body can use it. The first transformation occurs in the liver. Here, your body converts vitamin D to a chemical known as 25-hydroxyvitamin D, also called calcidiol.


What is the vitamin D blood test?

The 25-hydroxy vitamin D test is the best way to monitor vitamin D levels. The amount of 25-hydroxyvitamin D in your blood is a good indication of how much vitamin D your body has. The test can determine if your vitamin D levels are too high or too low.

The test is also known as the 25-OH vitamin D test and the calcidiol 25-hydroxycholecalcifoerol test. It can be an important indicator of osteoporosis (bone weakness) and rickets (bone malformation).


What function does Vitamin D serve in the body?

Vitamin D helps maintain healthy bones by promoting absorption of calcium and phosphorus, two key minerals needed for bones. Healthy bones reduce the incidence of fractures. Vitamin D is also required to maintain muscle strength, which helps prevent falls.

It is known that most cells express the Vitamin D receptor and about 3% of the human genome is directly or indirectly regulated by the vitamin D endocrine system. Vitamin D has a regulatory role for gene and receptors in cells.


Vitamin D levels are associated with:

  • Immune system activity
  • Prevention of certain cancers (e.g. colorectal cancer)
  • Cardiovascular disease prevention
  • Osteoarthritis
  • Fetus development
  • Risk for preeclampsia
  • Insulin resistance


Who is at high risk of having low levels of vitamin D?

  • people who do not get much exposure to the sun
  • older adults
  • people with obesity
  • babies who are breastfed only (formula is usually fortified with vitamin D)
  • people who have had gastric bypass surgery
  • people who have a disease that affects the intestines and makes it difficult for the body to absorb nutrients, such as Crohn’s disease


Symptoms of Vitamin D deficiency that you can identify yourself:

  • Fatigue
  • Fall sick easily
  • Bone/back pain
  • Digestion issues
  • Hair loss
  • Moody
  • Poor wound healing
  • Poor concentration


If your vitamin D levels are low and you are having symptoms of bone pain, a doctor may recommend a Bone DEXA scan to check bone density. Doctors use this painless scan to evaluate a person’s bone health.


Low blood levels of vitamin D usually mean one (or more) of the following:

  • you aren’t eating a balanced, complete diet
  • your intestines aren’t absorbing the vitamin properly
  • you’re not spending enough time outside to absorb adequate vitamin D levels through sun exposure


High vitamin D blood levels generally result from taking too many vitamin pills and other nutritional supplements. High doses of vitamin D can result in a condition called hypervitaminosis D. Hypervitaminosis is a rare but serious condition that could put you at risk for liver or kidney problems.


High levels are rarely due to consuming too much of the vitamin through foods or sun exposure.