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Vd7.5
Vitamin D3 Research
Probably helps
1,001 peer-reviewed studies
Showing the 991 most recent of 1001 studies.
All 1010 database studies by type: RCT 857 · Meta-Analysis 73 · Review 36 · Systematic Review 27 · Observational 10 · other 4 · Case Study 3
What the evidence says
Probably helps
Vitamin D3 helped in about half (7/12) of the studies that measured an effect — promising, but not unanimous.
Most evidence is from high-quality meta-analyses and randomised trials published 1994–2026 with a typical study size of 3,919 participants.
Based on 986 studies · 68 meta-analyses · 839 RCTs · 501,145 total participants
Confidence
High confidence
What the studies found
7helped4unclear1didn't help· 974 more without graded effect data
By outcome
Bone healthSupports bone mineral density and skeletal strength · 8-12 weeks
Probably helps960 studies
Therapeutic & clinical
Too few graded studies166 studies
Women's healthMay help manage menopausal symptoms like hot flashes and mood changes · 4-8 weeks · PCOS meta-analysis: may help follicle development and cycle regularity. A dysmenorrhoea meta-analysis found less period pain · 4-8 weeks · May help reduce menstrual discomfort and PMS symptoms · 1-3 cycles · Once untrustworthy trials were removed, a 2024 Cochrane review found the effect on pre-eclampsia, gestational diabetes and preterm birth very uncertain. It may lower severe bleeding after birth, from one trial · Ongoing
Depression & moodSmall reduction in depressive symptoms in pooled trials, at very low certainty · 4-8 weeks
Too few graded studies22 studies
Longevity & agingIn a Cochrane meta-analysis of RCTs, vitamin D3 modestly lowered mortality in older adults, and with calcium it lowers hip fracture. Vitamin D alone does not prevent fractures · 12+ weeks
Too few graded studies16 studies
Cognitive function
Too few graded studies12 studies
Joint pain & arthritis
Too few graded studies11 studies
Skin health
Too few graded studies10 studies
RecoveryBetter muscle recovery and reduced inflammation · 4-8 weeks
Too few graded studies9 studies
Cholesterol & lipids
Too few graded studies8 studies
Lean body mass & muscle growthSupports muscle protein synthesis and bone mineral density · 8-12 weeks
Too few graded studies7 studies
Men's vitalityNo cited trial measured testosterone or symptoms in men · 8-12 weeks
Too few graded studies6 studies
Fertility & reproductiveIn women with PCOS, randomised trials found more dominant follicles and higher ovulation rates with vitamin D, which are steps toward conception rather than measured pregnancies. · 4-12 weeks
Too few graded studies6 studies
Endurance & exercise performance
Too few graded studies5 studies
Neuroprotection & brain aging
Too few graded studies4 studies
Liver health
Too few graded studies4 studies
Energy & fatigue
Too few graded studies3 studies
Anxiety & stress
Too few graded studies2 studies
Migraine & headache
Too few graded studies2 studies
By the numbers
Pulled from 68 studies with measurable effects
Likely real effects
67%
across studies
People studied
501k
typical study: 3919 people
Strongest designs
907
68 pooled, 839 randomised
Showed benefit
58%
7/12 studies
How long studies ran
1–4 weeks
3
1–3 months
2
3+ months
6
Populations Studied
General population3
Adults3
Women with PCOS3
Adults with vitamin D deficiency2
Steady research
282 studies in the last 5 years · Latest meta-analysis: 2026
199420102026
1Type 2 diabetes incidenceRCTCited 18×n=22,220 · very large study2025
In plain English: Vitamin D supplementation did not reduce T2D in older US adults, but a modest reduction was observed when meta-analyzed with prior trials.
Tobias DK et al. · Nature communications (2025)
No clear effect
← WorseNo effectBetter →
Ancillary analysis of VITAL: 22,220 adults without T2D randomized to vitamin D3 2000 IU/day or placebo, with a meta-analysis of 3 additional trials.
T2D incidence (cases/1000py) at median follow-up of 5.3 y was 3.98 for vitamin D and 4.37 for placebo (hazard ratio [HR] = 0.91; 95% confidence interval [CI] = 0.76, 1.09).
Results did not differ by age, sex, BMI, or baseline 25-hydroxyvitamin D, and vitamin D had no effect on glycemic traits at 2 years.
2Hip fracture incidenceMeta-AnalysisCited 22×n=12,620 · very large study2023
In plain English: Daily oral supplementation 800 IU of vitamin D3 plus 1200 mg of calcium reduces hip fracture and non-vertebral fracture in older people.
Manoj P et al. · International journal of older people nursing (2023)
Large benefitCombination product. Contains: vitamin D3, calcium
← WorseNo effectBetter →
Likely real
The meta-analysis of seven RCTs on vitamin D3 plus calcium supplementation and hip fracture (n = 12,620) identified odds ratio (OR) of 0.75; 95% Confidence interval (CI): 0.64, 0.87; p = .0003.
800 IU vitamin D3 plus 1200 mg calcium reduced hip fracture (OR 0.69, 95% CI 0.58-0.82), while 800 IU plus 1000 mg calcium did not (OR 1.08, 95% CI 0.74-1.56).
A meta-analysis of the seven RCTs to identify the incidence of non-vertebral fracture gave the OR of 0.80; 95% CI: 0.72, 0.89; p < .0001.
In plain English: Our meta-analysis suggests a definitive and significant association between the protective role of vitamin D and COVID-19 incidence and ICU admission.
Sartini M et al. · Nutrients (2024)
Vitamin D supplementation had a protective effect against COVID-19 incidence in RCTs (OR 0.403, 95% CI 0.218-0.747).
Protective effect against COVID-19 incidence in analytical studies (OR 0.592, 95% CI 0.476-0.736).
Protective effect against ICU admission (OR 0.317, 95% CI 0.147-0.680).
4Pain intensity in dysmenorrheaMeta-AnalysisCited 1×n=687 · large study2024
In plain English: In conclusion, although substantial heterogeneity persists, vitamin D supplementation decreased pain intensity in patients with dysmenorrhea, especially in those with primary dysmenorrhoea.
Lin KC et al. · Nutrients (2024)
TSA revealed that the current RCTs provide sufficient information.
In subgroup analyses, vitamin D supplement reduced primary dysmenorrhoea pain but not secondary dysmenorrhoea pain.
In conclusion, although substantial heterogeneity persists, vitamin D supplementation decreased pain intensity in patients with dysmenorrhea, especially in those with primary dysmenorrhoea.
5Serum vitamin D repletionMeta-AnalysisCited 3×n=542 · large study2024
In plain English: Limited direct evidence supports a switch from daily to weekly cholecalciferol dosing; however, weekly supplementation was not demonstrably worse at repleting levels and decreased a patient's daily pill burden.
Bortolussi-Courval É et al. · Basic & clinical pharmacology & toxicology (2024)
Eight trials involving 542 patients with hypovitaminosis D. Weekly and daily cholecalciferol were not significantly different in correcting it (OR 1.5, 95% CI 0.3-6.9, I2 = 85.3%).
Most studies were at risk of bias, and the different doses being compared increased the heterogeneity.
Limited direct evidence supports a switch from daily to weekly cholecalciferol dosing; however, weekly supplementation was not demonstrably worse at repleting levels and decreased a patient's daily pill burden.
6Acute respiratory tract infection riskMeta-AnalysisCited 1,302×n=11,321 · very large study2017
In plain English: Vitamin D supplementation reduced the risk of acute respiratory tract infection, with stronger effects in those with profound deficiency.
Martineau AR et al. · BMJ (2017)
Noticeable benefit
← WorseNo effectBetter →
25 RCTs, 11 321 participants aged 0 to 95 years. Vitamin D reduced acute respiratory tract infection overall (adjusted OR 0.88, 95% CI 0.81 to 0.96).
Protection was seen with daily or weekly dosing (OR 0.81) but not with bolus doses (OR 0.97, 0.86 to 1.10).
With daily or weekly dosing, effects were stronger when baseline 25(OH)D was below 25 nmol/L (OR 0.30, 0.17 to 0.53) than at or above it (OR 0.75).
7Depression by vitamin D status (observational)Meta-AnalysisCited 576×n=31,424 · very large study2013
In plain English: Our analyses are consistent with the hypothesis that low vitamin D concentration is associated with depression, and highlight the need for randomised controlled trials of vitamin D for the prevention and treatment of depression to determine whether this association is causal.
Anglin RE et al. · British Journal of Psychiatry (2013)
One case-control study, ten cross-sectional studies and three cohort studies with a total of 31 424 participants. No supplementation trial was pooled.
Lower vitamin D levels were found in people with depression compared with controls (SMD = 0.60, 95% CI 0.23-0.97).
The cohort studies showed a significantly increased hazard ratio of depression for the lowest v. highest vitamin D categories (HR = 2.21, 95% CI 1.40-3.49).
8Follicular developmentMeta-AnalysisCited 70×n=502 · large study2017
In plain English: Evidence from available RCTs suggests vitamin D supplementation may be beneficial for follicular development and menstrual cycle regulation in patients with PCOS.
Fang F et al. · Complementary therapies in clinical practice (2017)
Huge harm
← WorseNo effectBetter →
Vitamin D supplementation had significant effect on the improvement of follicular development with a higher number of dominant follicles (OR, 2.34; 95% CI, 1.39 to 3.92).
Differences in regular menstrual cycles were also observed when metformin plus vitamin D was compared with metformin alone (OR, 1.85; 95% CI, 1.01 to 3.39).
Evidence from available RCTs suggests vitamin D supplementation may be beneficial for follicular development and menstrual cycle regulation in patients with PCOS.