Research, evidence, and sources
What this page is for
The vitamin D fact sheet explains what skin does in the sun. It does not say that a supplement improves time outside, and this page does not show vitamin D products for that purpose.
What the reviewed sources say
“Your body makes vitamin D when your bare skin is exposed to the sun.”
The body makes vitamin D when bare skin is in the sun. Clouds, smog, older age, and darker skin reduce how much the skin makes. Skin does not make vitamin D from sunlight that comes through a window.
Ultraviolet light from sunshine can cause skin cancer, so the fact sheet says to limit time in the sun. Sunscreen with an SPF of 15 or more is recommended for more than a few minutes outside. Sunscreen also limits vitamin D production. You cannot get too much vitamin D from sunshine, because skin limits the amount it makes. High blood levels almost always come from supplements, and those high levels can be harmful.
People who rarely put skin in the sun are among the groups that may have trouble getting enough vitamin D. That is a reason someone might talk with a clinician about diet or a blood test. It is not a finding that a vitamin D bottle belongs with a day outside. Bone health later in life is a separate page.
Vitamin D — Consumer Fact Sheet NIH Office of Dietary Supplements. Updated 2022-11-08. Retrieved 2026-10-07.
How to compare a label
“The nutrition label for a dietary supplement is called a “Supplement Facts” panel.”
Start with the Supplement Facts panel. The FDA’s labeling guide uses that name for a dietary supplement’s nutrition label.
Read the ingredient name, the amount per serving, and the serving size. A blend that lists several ingredients is a different product from a bottle that is only one of them. The price on a retailer card is the package price, not a price per serving, and a sale ribbon is not a checked comparison price.
- Dosage unit converterConvert grams, milligrams, and micrograms. IU converts only when the vitamin form is known.
- Price per servingSee what one serving costs from the container price and the servings on the label.
- Cost per labeled amountSee what a labeled amount of an ingredient costs. A second product is optional.
- Daily nutrient targetsPublished folate, magnesium, and vitamin A figures for a life stage.
Dietary Supplement Labeling Guide: Chapter IV. Nutrition Labeling U.S. Food and Drug Administration. Retrieved 2026-10-05.
Vitamin D and bone strength later in life
Labels you can open
These lists match a published ingredient. Opening one is not a suggestion that the ingredient meets this goal.
Sources
- Vitamin D — Consumer Fact Sheet NIH Office of Dietary Supplements. Updated 2022-11-08. Retrieved 2026-10-07.
- Dietary Supplement Labeling Guide: Chapter IV. Nutrition Labeling U.S. Food and Drug Administration. Retrieved 2026-10-05.