Vitamin D

Vitamin D

Best for

Lower COVID infection risk

Large effect, needs confirmation · 400–100000 IU/day for 26–39 weeks · 2 meta-analyses , n=1269.8k

139 papers · 21 claims · 196 outcomes scored · 11 positive

Evidence overview

Evidence overview Likely strong benefit

Vitamin D shows likely strong benefit for reducing everyday pain intensity and easing seasonal allergy symptoms, while broader outcome results remain mixed.

  • Across 7 studies (n=36,567), vitamin D reduced everyday pain intensity, the largest signal among listed outcomes.1
  • Research spans 139 papers and 196 outcomes, including strong signals for seasonal allergy symptoms.
  • Vitamin D works best when deficiency is present; bone and fracture results stay underwhelming in sufficient adults.1

Outcomes

What vitamin d actually does, by outcome

Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.

Outcome Effect Evidence Dose Weeks Rank
Lower COVID infection risk Large effect, needs confirmation
large
4 meta-analyses n=1270k Meta-analyzed 400–100000 IU 26–39 wk
Reduce everyday pain intensity Likely strong benefit
large
7 meta-analyses n=37k Meta-analyzed 140–300000 IU 31–276 wk #3/55
Ease seasonal allergy symptoms Likely strong benefit
large
2 meta-analyses n=1.3k Meta-analyzed 400–60000 IU 4–12 wk #1/7
Reduce everyday fatigue Large effect, needs confirmation
large
3 meta-analyses n=465 Meta-analyzed 40–100000 IU 24 wk #7/44
Raise vitamin D levels Proven benefit
moderate
51 meta-analyses n=70k Meta-analyzed 5–600000 IU 0–156 wk #1/2
Replenish immune fuel during TB treatment Proven benefit
moderate
51 meta-analyses n=70k Meta-analyzed 5–600000 IU 0–156 wk #1/2
Catch fewer colds and infections Proven benefit
moderate
6 meta-analyses n=34k Meta-analyzed 800–200000 IU 26–52 wk #5/17
Raise key nutrient levels in pregnancy Likely benefit
moderate
5 RCTs n=2.8k 20–150000 IU 4–26 wk
Reduce falls in older adults Likely modest benefit
small
5 meta-analyses n=183k Meta-analyzed 300–4800 IU 52–104 wk #2/5
Improve asthma control Proven modest benefit
small
6 meta-analyses n=4.6k Meta-analyzed 125–4000 mcg 12–48 wk #1/6
Build stronger nutrient stores in babies Faint early signal
small
3 RCTs n=305 20–150000 IU 4–26 wk
Lower fracture risk in older adults Probably doesn't help
small
7 meta-analyses n=193k Meta-analyzed 300–4000 IU 104–276 wk #3/3
Increase height growth in children Probably doesn't help
trivial
2 meta-analyses n=1.9k Meta-analyzed 200–300000 IU
Build stronger bones in growing kids Probably doesn't help
trivial
1 RCT n=665 1000–2800 IU
Build and maintain bone density Doesn't appear to help
trivial
2 meta-analyses n=610 Meta-analyzed 800–2000 IU 104 wk
Strengthen bone structure Probably doesn't help
trivial
1 RCT n=574 2000 IU 104 wk
Lower the chance of any cancer diagnosis Not enough research
1 RCT n=5.1k 100000–200000 IU
Feel full longer and crave less Not enough research
1 RCT n=77 25 mcg 13 wk
Boost willingness to exercise Not enough research
1 RCT n=77 25 mcg 13 wk
Improve overall diet quality Not enough research
1 RCT n=77 25 mcg 13 wk
Move more easily with aging Slight negative signal
trivial
4 meta-analyses n=3.2k Meta-analyzed 1000–100000 IU 12–104 wk

Forms & standardisation

Vitamin D3, or cholecalciferol, has the strongest trial coverage and raises 25(OH)D more reliably than D2 in head-to-head research.2 If you want the best-supported label, look for cholecalciferol and check whether the dose is listed in IU, not just a vague "vitamin D" claim.2 Softgels, drops, and tablets all work, so the form matters less than the actual dose and the D3 versus D2 choice.

Risk profile

Adverse events and known drug interactions

Safety events

hypercalcaemia severe
nephrolithiasis severe
postpartum haemorrhage severe
Serious adverse events (aggregate) severe
serious adverse events severe
pancreatitis severe
nephrocalcinosis severe
first fall with hospitalization severe

Drug interactions

Phenobarbital major decreases concentration
Tacrolimus major decreases concentration
Sirolimus major decreases concentration
Rifampin major decreases concentration
Phenytoin major decreases concentration
Carbamazepine major decreases concentration
Hydrochlorothiazide major increases toxicity
Primidone major decreases concentration
Warfarin major increases effect
Atorvastatin major decreases effect

Co-studied with

Supplements that share evidence with vitamin d

Frequently asked

Common questions

Is vitamin D3 better than D2?

Yes, vitamin D3 usually raises blood 25(OH)D more reliably than D2, based on head-to-head trials and meta-analysis. If your goal is to correct a low level, D3 is the better-studied pick.2

When should you take vitamin D?

Take it every day at a time you can stick with, and taking it with a meal that contains fat is a practical choice because vitamin D is fat-soluble.1 The big win is consistency, not timing hacks.

How much vitamin D do most studies use?

Many of the stronger studies sit around 800 to 4,000 IU/day, and the median effective dose in your evidence set for raising blood levels is about 4,500 IU/day.12 Some deficiency-repletion studies use much larger short-term doses, but those belong in a lab-guided plan.

Does vitamin D help bones?

It reliably raises vitamin D levels, but bone density and fracture results stay mixed and often disappoint when people are already sufficient.1 That makes vitamin D a good fix for deficiency, not a magic bone-builder.

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