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NutrientVitamin D
Vitamin D is a fat-soluble vitamin that your body mainly makes from sunlight. It helps the body absorb calcium and is important for strong bones, muscles and the immune system.
Vitamin D at a glance
WorksYes, for bones when deficientStrong
PossiblyMuscle strength and immunityPreliminary
SafeYes, within the recommended doseStrong
DoseOften 10 to 20 micrograms per day
106 studies17 answersupdated aug 2026
Evidence per claim
Important for strong bones
View evidence →Supplements help mainly when deficient
View evidence →May reduce falls in older adults
View evidence →Sunlight is the main natural source
View evidence →Practical use
For whom
People at higher risk of deficiency: older adults, people who get little sun, a darker skin or covering clothing, and the winter months.
Not for whom
High doses without a confirmed deficiency add little and can be harmful in excess. Routine high dosing is not needed.
Usual dose
Often 10 to 20 micrograms (400 to 800 IU) per day; with a confirmed deficiency sometimes more on a doctor advice.
Key caveats
More is not better; very high doses can be harmful. The effect on bones is clearest in people with a deficiency, together with enough calcium.
What we know, and don't
Known
Important for calcium absorption and strong bones
Supplements help most when a deficiency is confirmed
Sunlight is the main natural source
Not yet
Whether extra vitamin D helps healthy people without a deficiency
The best dose for immune or muscle effects
Whether it prevents cardiovascular disease or cancer
Common misconceptions
"Everyone should take high doses of vitamin D."
False. Mainly useful with a confirmed deficiency; more is not better.Strong evidence
"Vitamin D prevents cancer and heart disease."
Not shown. Large trials do not show this clearly.Strong evidence
"You get enough from food in winter."
Incomplete. Food contains little; sun and supplements are the main sources.Moderate evidence
How Vitamin D connects
Effects
Conditions
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