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Vd7.5
Vitamin D3 Research
Probably helps
971 peer-reviewed studies
What the evidence says
Probably helps
Vitamin D3 helped in about half (18/30) of the studies that measured an effect — promising, but not unanimous.
Most evidence is from high-quality meta-analyses and randomised trials published 1977–2026 with a typical study size of 871 participants.
Based on 970 studies · 70 meta-analyses · 844 RCTs · 566,413 total participants
Confidence
High confidence
What the studies found
18helped10unclear2didn't help· 940 more without graded effect data
By outcome
Bone healthSupports bone mineral density and skeletal strength · 8-12 weeks
Probably helps943 studies
Therapeutic & clinical
Mixed evidence154 studies
Women's healthMay help manage menopausal symptoms like hot flashes and mood changes · 4-8 weeks · Supports healthy estrogen metabolism and hormonal equilibrium · 4-8 weeks · May help reduce menstrual discomfort and PMS symptoms · 1-3 cycles · Provides essential nutrients for healthy pregnancy · Ongoing
Fertility & reproductiveMay support reproductive health and fertility markers · 4-12 weeks
Mostly mechanism / observational6 studies
Endurance & exercise performance
Mostly mechanism / observational5 studies
Neuroprotection & brain aging
Mostly mechanism / observational4 studies
Liver health
Mostly mechanism / observational4 studies
Energy & fatigue
Too few graded studies2 studies
Migraine & headache
Too few graded studies2 studies
By the numbers
Pulled from 79 studies with measurable effects
Likely real effects
67%
across studies
People studied
566k
typical study: 871 people
Strongest designs
914
70 pooled, 844 randomised
Showed benefit
60%
18/30 studies
How long studies ran
1–4 weeks
3
1–3 months
2
3+ months
8
Populations Studied
General population5
Women with PCOS3
Adults with vitamin D deficiency2
Individuals with vitamin D deficiency2
Steady research
251 studies in the last 5 years · Latest meta-analysis: 2026
197720012026
1Type 2 diabetes incidenceMeta-AnalysisCited 9×n=5,205 · very large study2025
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 →
Mean body mass index (BMI) was 27.5 kg/m2 (SD = 5.3), with 51% female and 17% Black race/ethnicity.
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).
In conclusion, Vitamin D supplementation did not reduce T2D in older US adults, but a modest reduction was observed when meta-analyzed with prior trials.
2Hip fracture incidenceMeta-AnalysisCited 21×n=5,676 · very large study2023
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 benefit
← 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.
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.
A meta-analysis of three RCTs on femoral neck bone mineral density (BMD) (n = 483) gave a mean difference of 1.21; 95% CI: -0.79, 3.20; p = .24.
4Pain intensity in dysmenorrheaMeta-AnalysisCited 1×n=687 · large study2024
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 2×n=542 · large study2024
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)
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.