Vitamin D

What vitamin D does

Your liver converts vitamin D from sun, food or supplements into 25-hydroxyvitamin D, the main circulating form, and your kidneys turn some of that into the active hormone. It helps your gut absorb calcium and phosphate, which bones need. Severe deficiency causes soft, painful bones (osteomalacia) in adults and muscle weakness.

Who is more likely to run low

• Older adults, whose skin makes less vitamin D.
• People with limited sun exposure or darker skin.
• People with obesity or a history of gastric bypass.
• People with conditions that impair fat absorption, such as Crohn's or celiac disease.
• People with kidney or liver disease, or who take certain medicines.

How to read a level

The NIH Office of Dietary Supplements summarizes National Academies thresholds: below 12 ng/mL (30 nmol/L) is a risk of deficiency, 12 to 20 ng/mL may be inadequate for some people, 20 ng/mL (50 nmol/L) or above is enough for most, and above 50 ng/mL (125 nmol/L) is linked to possible harm.

You may see 30 ng/mL quoted as a target. The Endocrine Society used that figure in 2011 but no longer endorses it; its 2024 guideline found no trial evidence for any specific target level.

Should you be tested?

The U.S. Preventive Services Task Force found insufficient evidence to recommend screening adults without symptoms. The Endocrine Society's 2024 guideline suggests against routine testing in healthy adults, while supporting testing when there is a specific reason, such as low calcium or a bone disorder.

That guideline does suggest empiric supplementation for adults 75 and older and for people with high-risk prediabetes, alongside lifestyle change.

What supplements can and cannot do

In the large VITAL trial, 2,000 IU of vitamin D3 daily did not reduce fractures, heart attacks, strokes or overall cancer rates in generally healthy adults. Supplements are useful for correcting deficiency, but more is not better: excess intake can raise calcium and cause nausea, weakness and kidney problems.

At HealifyMD

If vitamin D testing is appropriate for you, your HealifyMD clinician can include it in your lab work and discuss the result alongside your bone, muscle and overall health. Labs are priced separately from treatment.

Getting a meaningful result

Vitamin D levels change with the seasons, so a test in late winter often reads lower than one in late summer. If you are tracking a deficiency, testing at a similar time of year and at the same lab makes comparisons fairer. Tell your clinician about all supplements, including multivitamins and fortified foods, so the total dose is clear.