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 summary

Evidence summary

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.

Lower COVID infection risk Large effect, needs confirmation

Front-line immune cells intercept viruses more effectively at first contact.

4 meta-analyses n=1270k 400–100000 IU 26–39 wk
Reduce everyday pain intensity Likely strong benefit

Lower intensity, fewer flares, and longer stretches of relief.

7 meta-analyses n=37k 140–300000 IU 31–276 wk #3/55
Ease seasonal allergy symptoms Likely strong benefit

Breathe easier and sneeze less during pollen season.

2 meta-analyses n=1.3k 400–60000 IU 4–12 wk #1/7
Reduce everyday fatigue Large effect, needs confirmation

Less of that heavy, worn-out feeling that makes simple tasks feel like a chore.

3 meta-analyses n=465 40–100000 IU 24 wk #7/44
Raise vitamin D levels Proven benefit

Closes the deficiency gap most people don't know they have.

51 meta-analyses n=70k 5–600000 IU 0–156 wk #1/2
Replenish immune fuel during TB treatment Proven benefit

Restores a nutrient the immune system burns through faster during active TB.

51 meta-analyses n=70k 5–600000 IU 0–156 wk #1/2
Catch fewer colds and infections Proven benefit

Your immune barriers intercept more viruses before they take hold.

6 meta-analyses n=34k 800–200000 IU 26–52 wk #5/17
Raise key nutrient levels in pregnancy Likely benefit

Gets you to sufficient levels before delivery.

5 RCTs n=2.8k 20–150000 IU 4–26 wk
Reduce falls in older adults Likely modest benefit

Stronger legs and steadier balance keep you upright on uneven ground.

5 meta-analyses n=183k 300–4800 IU 52–104 wk #2/5
Improve asthma control Proven modest benefit

Fewer rescue inhaler puffs, fewer nighttime wake-ups, fewer scary episodes.

6 meta-analyses n=4.6k 125–4000 mcg 12–48 wk #1/6
Build stronger nutrient stores in babies Faint early signal

Fills the gap before your baby can build their own stores from sunlight.

3 RCTs n=305 20–150000 IU 4–26 wk
Lower fracture risk in older adults Probably doesn't help

Fewer hip, spine, forearm, and other fractures from weakened bones.

7 meta-analyses n=193k 300–4000 IU 104–276 wk #3/3
Increase height growth in children Probably doesn't help

Fills the nutritional gaps that slow a child's growth curve.

2 meta-analyses n=1.9k 200–300000 IU
Build stronger bones in growing kids Probably doesn't help

Children lay down more bone mass during the years that matter most.

1 RCT n=665 1000–2800 IU
Build and maintain bone density Doesn't appear to help

Keeps mineral packed tightly into hip, spine, and whole-body bone.

2 meta-analyses n=610 800–2000 IU 104 wk
Strengthen bone structure Probably doesn't help

Builds thicker walls and a denser internal framework so bones resist fracture.

1 RCT n=574 2000 IU 104 wk
Lower the chance of any cancer diagnosis Not enough research

Across long studies, fewer new cancer cases show up at any site.

1 RCT n=5.1k 100000–200000 IU
Feel full longer and crave less Not enough research

Genuine satiety replaces the constant urge to snack or overeat.

1 RCT n=77 25 mcg 13 wk
Boost willingness to exercise Not enough research

Tips the internal balance from wanting to rest toward wanting to move.

1 RCT n=77 25 mcg 13 wk
Improve overall diet quality Not enough research

You naturally gravitate toward more fiber, better fats, and less junk.

1 RCT n=77 25 mcg 13 wk
Move more easily with aging Slight negative signal

Stand, walk, turn, and handle stairs with less effort and more confidence.

4 meta-analyses n=3.2k 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

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.

Track vitamin d in the app

Log doses, check interactions, compare it to alternatives — all backed by the same evidence base.

One email when we launch. No spam, no selling.

Want personalized recommendations?

Show me what works for me