Vitamin D helps you absorb calcium and keeps bones and muscles working. Skin makes it from sunlight, so needs from pills depend a lot on season and latitude.
These are doses tested in research, not personal advice. Some exceed the upper limit because they were short courses or given under medical care.
Strong evidenceStrong: meta-analyses of randomised trials or a large trial, with results that agree.Based on 1 randomised trial, 1 review or position paper.How grades workNo benefit or harm found
Prevent cancer or heart disease in healthy older adults
50 µg a day
VITAL gave 2000 IU (50 µg) a day to 25,871 adults for about 5 years. It did not lower cancer or major cardiovascular events compared with placebo. Later meta-analyses saw lower cancer deaths, but not fewer cancers.
Moderate evidenceModerate: smaller trials, mixed results or official guidance.Based on 1 meta-analysis.How grades work
Fewer respiratory infections (colds, flu)
10-25 µg a day
Meta-analysis of randomised trials: overall the protective effect was small. Daily doses of 400 to 1000 IU (10 to 25 µg) showed the clearest benefit (odds ratio 0.70), while large monthly or weekly bolus doses did not.
These targets come from named organisations, not from EFSA or the NIH. They are listed so you can see the case for a higher intake, with the source behind each one.
Moderate evidenceModerate: smaller trials, mixed results or official guidance.Based on 1 official reference.How grades workMedical or scientific body
Linus Pauling Institute: Daily supplement for healthy adults
50 µg a day
The Linus Pauling Institute recommends that generally healthy adults take 2,000 IU (50 µg) of supplemental vitamin D a day, more than three times the EFSA adequate intake of 15 µg. It is a research institute's recommendation, not an official reference value.
Strong evidenceStrong: meta-analyses of randomised trials or a large trial, with results that agree.Based on 1 official reference.How grades workMedical or scientific body
Endocrine Society: Who should take extra vitamin D
The 2024 guideline suggests extra vitamin D above the official intake only for people aged 75 and over, in pregnancy, for high-risk prediabetes, and for children and teenagers. It suggests against extra vitamin D for healthy adults under 75, and against routine blood testing. It also says the best dose is unclear from the trials.
Moderate evidenceModerate: smaller trials, mixed results or official guidance.Based on 1 official reference, 1 study.How grades workBased on a blood level
The Society no longer endorses its earlier blood targets of 30 ng/ml for "sufficiency" or 20 to 30 ng/ml for "insufficiency", because trials do not show a level that predicts who benefits from supplements. The NIH describes 20 ng/ml (50 nmol/l) and above as adequate for nearly everyone.
Why: D3 raises blood vitamin D more than D2 when given as large weekly or monthly doses. With daily doses the two were similar. D3 is also the form your skin makes.
Alternatives: D2 is fine for vegans if no vegan D3 (from lichen) is available. Take it with a meal that contains fat.
CalciumStrong evidenceStrong: meta-analyses of randomised trials or a large trial, with results that agree.Based on 1 official reference.How grades work
Vitamin D is needed to absorb calcium in the gut. Calcium supplements work best when your vitamin D intake is adequate.
Often sold together. A meta-analysis of 8 trials (971 people) found vitamin K plus vitamin D raised bone density a little more than no treatment, especially with K2 under 500 µg a day. The effect was small.
Oily fish (salmon, herring, mackerel), egg yolks, fortified milk and spreads, UV-exposed mushrooms.
Interactions
Usually taken with calcium for bones. Take with a meal containing fat for better absorption. High doses with thiazide diuretics can raise blood calcium.
Safety
Too much over months can raise blood calcium (nausea, kidney stones). Stay under the safe limit unless a doctor treats a measured deficiency.
Pregnant, breastfeeding, on medication, or managing a health condition? Check with a doctor or pharmacist before starting a supplement.