Vitamin D

Not a botanical (vitamin) · supplement

Evidence tier: moderate

In plain terms

Vitamin D is made in the skin from sunlight and found in a small number of foods, such as oily fish, egg yolks and fortified foods. In a large trial of healthy midlife and older adults not selected for low levels, extra vitamin D did not lower the risk of fractures.

How it works

Vitamin D is converted in the liver to 25(OH)D and in the kidney to the active hormone calcitriol, which increases calcium and phosphate absorption from the gut and keeps bone mineralised.

What the evidence says

Essential for calcium absorption and healthy bones, teeth and muscles; deficiency causes rickets and osteomalacia (NIH ODS, NHS). Intake advice is official and clear: UK 10 mcg a day in autumn and winter for everyone, year round for at risk groups; US RDA 15 to 20 mcg. The extras people buy it for did not hold up in large trials: in VITAL 2,000 IU a day did not reduce fractures, an evidence review found with moderate certainty that it does not prevent falls in community dwelling older adults, trials did not show it prevents or treats depression (NIH ODS), and a 2025 meta analysis found no significant reduction in acute respiratory infections (OR 0.94, 0.88 to 1.00, PMID 39993397). Graded moderate for its core role of preventing low status, not for any symptom.

Dose and timing

10 mcg (400 IU) a day in the UK; 15 mcg (600 IU) a day in the US to age 70 and 20 mcg (800 IU) over 70. Upper limit 100 mcg (4,000 IU) a day for adults.

D3 is preferred over D2 because it raises and holds blood levels better. Take with a meal containing some fat. Do not exceed 100 mcg (4,000 IU) a day unless a doctor advises. With thiazide diuretics, kidney disease or hyperparathyroidism, check with a doctor first. [NIH ODS; NHS]

Dose by form

• tablet or capsule: UK adults 10 mcg (400 IU) a day in autumn and winter, year round if rarely outdoors, in a care home, covering most skin or with dark skin [NHS]; US RDA 15 mcg (600 IU) a day to age 70, 20 mcg (800 IU) over 70 [NIH ODS]
• drops (babies and young children): Breastfed babies from birth to 1 year 8.5 to 10 mcg a day; children 1 to 4 years 10 mcg a day; not needed on more than 500 ml of formula a day [NHS]

Preparation forms

• tablet
• capsule
• softgel
• liquid

Safety

Pregnancy: safe

Breastfeeding: safe

Active compounds: cholecalciferol (D3), ergocalciferol (D2)

Remedies using Vitamin D · Browse by body system · Check it against what you take

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.