Vitamin D3
Cholecalciferol
The 'sunshine' hormone-vitamin for bone and immunity.
Evidence tier
Strong
Research weight
Citations
16 verified / 16
Classification
Vitamin
❝
What the evidence says. Graded strong for correcting deficiency — bone density, falls and fractures in deficient or older adults — not for already-replete people, where large trials (VITAL) show little benefit for heart disease or cancer. Most valuable when blood levels are genuinely low. (Strong evidence: Multiple high-quality RCTs / meta-analyses with consistent effects.)
What is Vitamin D3?
Vitamin D3 (Cholecalciferol) is a vitamin used for bone health. NutriDex grades the human evidence as Strong. Vitamin D regulates calcium absorption and bone mineralization and modulates immune function. Deficiency is widespread, especially in northern latitudes and darker skin. Correcting deficiency clearly benefits bone density and reduces fracture risk (with calcium). Broad supplementation in already-replete people shows little benefit for cardiovascular disease or cancer (VITAL trial), so it is most valuable when blood levels are low. Possible small reduction in respiratory infections.
Purported Benefits
✓Bone health
✓Immune support
✓Mood (if deficient)
✓Muscle function
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Fracture / bone healthBenefit mainly when correcting deficiency (with calcium); VITAL found no fracture reduction in replete adults. | Mixed | ↔ mixed · small | 3 |
| Respiratory infection preventionMeta-analysis of 37 RCTs found modest protection (OR 0.92), concentrated at daily 400-1000 IU. | Moderate | ↑ benefit · small | 2 |
| Type 2 diabetes progression (prediabetes)IPD meta-analysis found ~15% lower progression to diabetes in prediabetic adults. | Moderate | ↑ benefit · small | 2 |
| Depression / moodMeta-analysis of 20 RCTs found moderate symptom reduction (SMD -0.36); benefit likely greatest if deficient. | Moderate | ↑ benefit · small | 1 |
| Falls / muscle functionDaily 800-1000 IU reduced falls (RR 0.85) in deficient elderly, but high-dose intermittent dosing may increase falls. | Moderate | ↔ mixed · small | 2 |
| Cardiovascular disease / cancer incidenceVITAL RCT (25,871 replete adults) found no reduction in CVD or cancer over ~5 years. | Strong | — no effect · negligible | 1 |
| Autoimmune disease preventionVITAL secondary analysis found 22% fewer autoimmune diagnoses (HR 0.78), a single trial needing confirmation. | Preliminary | ↑ benefit · small | 1 |
Dosing & Compounds
Typical Dose
1,000–2,000 IU/day maintenance; higher to correct deficiency under testing.
Active Compounds
Safety & Cautions
Tolerable upper limit ~4,000 IU/day for most adults; toxicity (hypercalcemia) occurs with chronic very high intake (>10,000 IU/day). Use caution and clinician oversight in sarcoidosis or other granulomatous disease and with thiazide diuretics — both raise calcium. Prefer a steady daily dose: large infrequent 'bolus' dosing has been linked to more falls and, in a 2024 meta-analysis, a signal of increased hip-fracture risk in women. Educational only — always check with your doctor or pharmacist before combining Vitamin D3 with any medicine.
Key Studies ★ 16 studies
Meta-analysis
Pittas 2023 (IPD meta-analysis)
✓ PubMed
Individual-participant meta-analysis of 3 RCTs (4,190 adults with prediabetes) found vitamin D reduced progression to type 2 diabetes by 15% (3-year absolute risk reduction ~3.3%).
Meta-analysis
Han 2024 (meta-analysis)
✓ PubMed
Meta-analysis of 7 RCTs (71,899 healthy older adults) found vitamin D did not reduce overall fracture incidence (RR 1.03), with a signal of increased hip fracture risk in women (RR 1.34).
Meta-analysis
Kuznia 2023 (depression meta-analysis)
✓ PubMed
Meta-analysis of 20 RCTs found vitamin D supplementation produced a moderate, statistically significant reduction in depressive symptom scores (SMD -0.36, 95% CI -0.52 to -0.20).
Meta-analysis
Zhang 2024 (systematic review/meta-analysis)
✓ Full text
Meta-analysis of 11 RCTs (5,221 adults with prediabetes) found vitamin D supplementation reduced progression to type 2 diabetes by about 10% and increased regression to normoglycemia.
network meta-analysis
Wu 2024 (network meta-analysis)
✓ PubMed
Network meta-analysis of 35 RCTs (~58,937 older adults) found vitamin D 800-1000 IU/day lowered fall risk versus placebo (RR 0.85, 95% CI 0.74-0.95), with a 22% reduction for daily dosing (RR 0.78), benefit concentrated in vitamin D-deficient individuals.
meta-analysis
2024 COVID-19 mortality meta-analysis
✓ PubMed
Meta-analysis of 14 RCTs found vitamin D supplementation did not reduce mortality in patients with moderate/severe COVID-19 (OR 1.16, 95% CI 0.84-1.59), with no benefit regardless of dose or baseline vitamin D status.
Meta-analysis
Jolliffe 2021 (meta-analysis)
✓ PubMed
Meta-analysis of 37 RCTs (~46,000 participants) found vitamin D modestly reduced acute respiratory infection risk (OR 0.92), with benefit concentrated at daily doses of 400-1000 IU for up to 12 months.
Meta-analysis
Guo 2022 (systematic review/meta-analysis)
✓ PubMed
Meta-analysis of 12 RCTs (72,669 participants) found vitamin D did not reduce overall cancer mortality (RR 0.96) though it was associated with lower lung cancer mortality (RR 0.63).
meta-analysis
Keum 2022 (British Journal of Cancer meta-analysis)
✓ PubMed
Meta-analysis of RCTs found daily (but not infrequent large-bolus) vitamin D supplementation reduced total cancer mortality by 13% (RR 0.87, 95% CI 0.78-0.96), while having no effect on total cancer incidence (RR 0.99).
Meta-analysis
Martineau 2017 meta-analysis
✓ PubMed
Modest protection against acute respiratory infections.
Guideline
Demay 2024 (Endocrine Society guideline)
✓ PubMed
Endocrine Society guideline concludes healthy adults aged 18-74 do not benefit from vitamin D above the RDA or from routine 25(OH)D testing, but recommends empiric supplementation for children, pregnancy, adults >75, and high-risk prediabetes.
Guideline
Endocrine Society Guideline (Demay/Shah et al.) 2024
✓ PubMed
Authoritative society guideline (systematic review of 151 studies): recommends against routine empiric vitamin D or 25(OH)D screening in healthy adults 19-74; identifies benefit only in specific groups - high-certainty very small mortality reduction in adults >75, reduced respiratory infections in children, and moderate-certainty reduced progression to diabetes in prediabetes. Warns high-dose intermittent dosing may increase falls.
randomized controlled trial
Hahn 2022 (VITAL RCT)
✓ PubMed
In the VITAL RCT (25,871 older adults, 2000 IU/day for a median 5.3 years), vitamin D supplementation reduced incident autoimmune disease by 22% (HR 0.78, 95% CI 0.61-0.99) versus placebo.
RCT
LeBoff et al. (VITAL fractures) 2022
✓ PubMed
Large RCT (n=25,871, 2000 IU/day, median 5.3 yr) in generally healthy adults not selected for deficiency: vitamin D3 did NOT reduce total fractures (HR 0.98, 95% CI 0.89-1.08), nonvertebral (HR 0.97), or hip fractures (HR 1.01); no effect modification by baseline 25(OH)D.
RCT
VITAL 2019
✓ PubMed
No reduction in CVD or cancer in replete adults over 5 years.
Study
Bischoff-Ferrari 2009
✓ PubMed
Higher-dose D reduced fracture risk in older adults.