Vitamin D

What it is

• Vitamin D is made in the skin when sunlight's ultraviolet rays strike it.
• In foods and supplements, vitamin D comes in two main forms, D2 and D3.
• Few foods naturally contain vitamin D. Fatty fish and fish liver oils are among the best sources.
• Fortified foods provide most of the vitamin D in American diets.

Source: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗

How it's thought to work

• Vitamin D helps the gut absorb calcium and keeps calcium and phosphate levels in the blood adequate for normal bone formation.
• Vitamin D from sun, food, and supplements is inactive until the body changes it twice, first in the liver and then mainly in the kidney.
• Vitamin D also plays a role in reducing inflammation and in cell growth, nerve and muscle function, immune function, and blood sugar handling.
• Fat in the gut helps vitamin D absorption, but some is absorbed without it.

Source: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗

What people use it for

• Without enough vitamin D, bones can become thin, brittle, or misshapen.
• Enough vitamin D prevents rickets in children and osteomalacia (soft bones) in adults.
• MedlinePlus says vitamin D3 is used as a supplement when the diet does not provide enough vitamin D.

Sources: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗ · MedlinePlus (NIH): Cholecalciferol (Vitamin D3): MedlinePlus Drug Information ↗

What the research has found so far

In trials, vitamin D and calcium may have raised bone density in some postmenopausal women and older men, but effects on falls and fractures are unclear. Trials have generally failed to show that vitamin D supplements reduce cancer rates.

Source: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗

On Vitamin D and aging, PubMed lists 194 trials in people, 760 studies that watched people over time, 603 animal and lab studies. See the counts and searches

Side effects and risks

MedlinePlus lists loss of appetite, weight loss, nausea, vomiting, and constipation as possible side effects. Overdose symptoms may include loss of appetite, weight loss, nausea, vomiting, constipation, and weakness.

Source: MedlinePlus (NIH): Cholecalciferol (Vitamin D3): MedlinePlus Drug Information ↗

Who should be careful, and drug interactions

• Older adults are at higher risk of low vitamin D, partly because skin makes less of it with age.
• MedlinePlus says to tell a doctor if pregnant, planning pregnancy, or breast-feeding.
• People with obesity might need more vitamin D to reach the same blood levels as people of normal weight.
• Black Americans might have a greater risk of falls and fractures with daily vitamin D intakes of 50 mcg (2,000 IU) or more.

Sources: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗ · MedlinePlus (NIH): Cholecalciferol (Vitamin D3): MedlinePlus Drug Information ↗

Approval and legal status

The FDA has approved UV-treated mushroom powder as a food additive that is a source of vitamin D2. Vitamin D3 is available without a prescription, but a doctor may prescribe it for certain conditions. The US requires infant formula to be fortified with 1 to 2.5 mcg of vitamin D per 100 kcal.

Sources: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗ · MedlinePlus (NIH): Cholecalciferol (Vitamin D3): MedlinePlus Drug Information ↗

Amounts used in studies

What studies or labels describe, not a recommendation.

• Recommended daily amounts range from 15 to 20 mcg (600 to 800 IU) for adults.
• One large trial used 50 mcg (2,000 IU) of vitamin D3 a day in adults over 50.
• A trial in older Black women used 60 to 120 mcg (2,400 to 4,800 IU) of vitamin D3 daily.
• The label form of vitamin D3 comes as capsules, gel capsules, gummies, tablets, and liquid drops taken by mouth.

Sources: NIH Office of Dietary Supplements: Vitamin D - Health Professional Fact Sheet ↗ · MedlinePlus (NIH): Cholecalciferol (Vitamin D3): MedlinePlus Drug Information ↗

Roughly what it costs

The 11 products we list that contain Vitamin D cost from $8.59 to $40, as read from the makers' pages. See the products

Questions to ask your doctor

• Is Vitamin D a sensible option for me, given my health and the medicines I take?
• Could Vitamin D interact with any medicine or supplement I already take?
• What side effects should I watch for, and when should I stop or call you?
• Supplements aren't checked by the FDA before sale. Is there a brand or a third-party test seal you would trust?
• How would we tell whether it is helping, and when should we review it?