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
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.
Front-line immune cells intercept viruses more effectively at first contact.
Lower intensity, fewer flares, and longer stretches of relief.
Breathe easier and sneeze less during pollen season.
Less of that heavy, worn-out feeling that makes simple tasks feel like a chore.
Closes the deficiency gap most people don't know they have.
Restores a nutrient the immune system burns through faster during active TB.
Your immune barriers intercept more viruses before they take hold.
Gets you to sufficient levels before delivery.
Stronger legs and steadier balance keep you upright on uneven ground.
Fewer rescue inhaler puffs, fewer nighttime wake-ups, fewer scary episodes.
Fills the gap before your baby can build their own stores from sunlight.
Fewer hip, spine, forearm, and other fractures from weakened bones.
Fills the nutritional gaps that slow a child's growth curve.
Children lay down more bone mass during the years that matter most.
Keeps mineral packed tightly into hip, spine, and whole-body bone.
Builds thicker walls and a denser internal framework so bones resist fracture.
Across long studies, fewer new cancer cases show up at any site.
Genuine satiety replaces the constant urge to snack or overeat.
Tips the internal balance from wanting to rest toward wanting to move.
You naturally gravitate toward more fiber, better fats, and less junk.
| Outcome | Effect | Evidence | Dose | Weeks | Rank |
|---|---|---|---|---|---|
| Lower COVID infection risk Large effect, needs confirmation | | 4 meta-analyses n=1270k Meta-analyzed | 400–100000 IU | 26–39 wk | — |
| Reduce everyday pain intensity Likely strong benefit | | 7 meta-analyses n=37k Meta-analyzed | 140–300000 IU | 31–276 wk | #3/55 |
| Ease seasonal allergy symptoms Likely strong benefit | | 2 meta-analyses n=1.3k Meta-analyzed | 400–60000 IU | 4–12 wk | #1/7 |
| Reduce everyday fatigue Large effect, needs confirmation | | 3 meta-analyses n=465 Meta-analyzed | 40–100000 IU | 24 wk | #7/44 |
| Raise vitamin D levels Proven benefit | | 51 meta-analyses n=70k Meta-analyzed | 5–600000 IU | 0–156 wk | #1/2 |
| Replenish immune fuel during TB treatment Proven benefit | | 51 meta-analyses n=70k Meta-analyzed | 5–600000 IU | 0–156 wk | #1/2 |
| Catch fewer colds and infections Proven benefit | | 6 meta-analyses n=34k Meta-analyzed | 800–200000 IU | 26–52 wk | #5/17 |
| Raise key nutrient levels in pregnancy Likely benefit | | 5 RCTs n=2.8k | 20–150000 IU | 4–26 wk | — |
| Reduce falls in older adults Likely modest benefit | | 5 meta-analyses n=183k Meta-analyzed | 300–4800 IU | 52–104 wk | #2/5 |
| Improve asthma control Proven modest benefit | | 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 | | 3 RCTs n=305 | 20–150000 IU | 4–26 wk | — |
| Lower fracture risk in older adults Probably doesn't help | | 7 meta-analyses n=193k Meta-analyzed | 300–4000 IU | 104–276 wk | #3/3 |
| Increase height growth in children Probably doesn't help | | 2 meta-analyses n=1.9k Meta-analyzed | 200–300000 IU | — | — |
| Build stronger bones in growing kids Probably doesn't help | | 1 RCT n=665 | 1000–2800 IU | — | — |
| Build and maintain bone density Doesn't appear to help | | 2 meta-analyses n=610 Meta-analyzed | 800–2000 IU | 104 wk | — |
| Strengthen bone structure Probably doesn't help | | 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 | | 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
Drug interactions
Co-studied with
Supplements that share evidence with vitamin d
-
Calcium 32 shared outcomes · d=0.25 -
Omega3 13 shared outcomes · d=0.04 -
Magnesium 10 shared outcomes · d=0.59 - Calciumcarbonate 8 shared outcomes · d=0.33
-
Riboflavin 5 shared outcomes · d=0.46 -
Vitaminb6 5 shared outcomes · d=0.46 -
Vitaminb12 5 shared outcomes · d=0.46 -
Inositol 5 shared outcomes · d=0.46 -
Probiotics 5 shared outcomes · d=0.46 -
Zinc 5 shared outcomes · d=0.46 -
Carotene 5 shared outcomes · d=0.46 -
Iron 5 shared outcomes · d=0.46 -
Iodine 5 shared outcomes · d=0.46 -
Vitaminb9 5 shared outcomes · d=0.46 -
Mineral 4 shared outcomes · d=0.33 - Mediumchaintriglycerides 3 shared outcomes · d=0.56
-
Cocoa 3 shared outcomes · d=0.56 - Xylitol 3 shared outcomes · d=0.56
-
Methylsulfonylmethane 3 shared outcomes · d=0.56 -
Flaxseedoil 3 shared outcomes · d=0.56 -
Vitamind 2 shared outcomes · d=0.00
Frequently asked
Common questions
Is vitamin D3 better than D2?
When should you take vitamin D?
How much vitamin D do most studies use?
Does vitamin D help bones?
Related
More evidence for Vitamin D
Ranking
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Evidence brief
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Evidence brief
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Ingredient evidence
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