We use essential cookies (authentication, your saved goals/stack) by default. With your permission we’ll also enable privacy-respecting analytics (Vercel Web Analytics, anonymous load-time metrics) and error-replay diagnostics (Sentry — DOM snapshots only when an error fires) so we can fix bugs faster. Learn more about cookies
Vd7.5
Vitamin D3 Research
Probably helps
975 peer-reviewed studies
What the evidence says
Probably helps
Vitamin D3 helped in about half (17/28) 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 687 participants.
Based on 970 studies · 69 meta-analyses · 838 RCTs · 560,168 total participants
Confidence
High confidence
What the studies found
17helped9unclear2didn't help· 942 more without graded effect data
By outcome
Bone healthSupports bone mineral density and skeletal strength · 8-12 weeks
Probably helps943 studies
Therapeutic & clinical
Probably helps156 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 / observational5 studies
Neuroprotection & brain aging
Mostly mechanism / observational4 studies
Liver health
Mostly mechanism / observational4 studies
Anxiety & stress
Too few graded studies2 studies
Energy & fatigue
Too few graded studies2 studies
Migraine & headache
Too few graded studies2 studies
By the numbers
Pulled from 76 studies with measurable effects
Likely real effects
64%
across studies
People studied
560k
typical study: 687 people
Strongest designs
907
69 pooled, 838 randomised
Showed benefit
61%
17/28 studies
How long studies ran
1–4 weeks
3
1–3 months
2
3+ months
7
Populations Studied
General population5
Adults with vitamin D deficiency2
Individuals with vitamin D deficiency2
Adults2
Steady research
255 studies in the last 5 years · Latest meta-analysis: 2026
197720012026
1Type 2 diabetes incidenceMeta-Analysisn=5,205 · 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 →
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.
2COVID-19 infection riskMeta-Analysisn=25,000 · very large study2024
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).
3Pain intensity in dysmenorrheaMeta-Analysisn=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.
4Serum vitamin D repletionMeta-Analysisn=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)
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.
5Acute respiratory tract infection riskMeta-Analysisn=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 →
12% reduction in respiratory infections overall
70% reduction in severely deficient individuals
Daily/weekly dosing more effective than large boluses
7Follicular developmentMeta-Analysisn=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.