Vitamin D is a nutrient that is essential for healthy bones and teeth. There are two forms of vitamin D that are important for nutrition: vitamin D2 and vitamin D3. Vitamin D2 mainly comes from fortified foods like breakfast cereals, milk, and other dairy items. Vitamin D3 is made by your own body when you are exposed to sunlight. It is also found in some foods, including eggs and fatty fish, such as salmon, tuna, and mackerel.

In your bloodstream, vitamin D2 and vitamin D3 are changed into a form of vitamin D called 25 hydroxyvitamin D, also known as 25(OH)D. A vitamin D blood test measures the level of 25(OH)D in your blood. Abnormal levels of vitamin D can indicate bone disorders, nutrition problems, organ damage, or other medical conditions.

Other names: 25-hydroxyvitamin D, 25(OH)D

A vitamin D test is used to screen for or monitor bone disorders. It is also sometimes used to check vitamin D levels in people with chronic illnesses such as asthma, psoriasis, and certain autoimmune diseases.

Your health care provider may have ordered a vitamin D test if you have symptoms of a vitamin D deficiency (not enough vitamin D). These symptoms include:

• Bone weakness
• Bone softness
• Bone malformation (in children)
• Fractures

The test may be ordered if you are at a higher risk for a vitamin D deficiency. Risk factors include:

• Osteoporosis or other bone disorder
• Previous gastric bypass surgery
• Age; vitamin D deficiency is more common in older adults.
• Obesity
• Lack of exposure to sunlight
• Having a darker complexion
• Difficulty absorbing fat in your diet

In addition, breastfed babies may be at a higher risk if they aren't taking vitamin D supplements.

If your results show a deficiency in vitamin D, it may mean you are:

• Not getting enough exposure to sunlight
• Not getting enough vitamin D in your diet
• Having trouble absorbing vitamin D in your food

A low result may also mean your body is having trouble using the vitamin as it should, and may indicate kidney or liver disease.

If your results show you have an excess of (too much) vitamin D, it is most likely due to taking too many vitamin pills or other supplements. Too much vitamin D can cause damage to your organs and blood vessels.

To learn what your results mean, talk to your health care provider.

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