Vitamin D3
Strong EvidenceThe sunshine vitamin — 1 in 5 UK adults are deficient, rising to 1 in 3 in winter.
Not medical advice
Nutripedia summarises published peer-reviewed research. This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before taking any supplement.
Vitamin D3 (cholecalciferol) is a fat-soluble secosteroid hormone essential for calcium absorption, bone mineralisation, and immune regulation. UK latitude (>52°N) means cutaneous synthesis is negligible October–March. NDNS data shows 18% of UK adults are deficient (25[OH]D <25 nmol/L), rising to 31% in winter and 57% among South Asian populations. D3 is significantly more bioavailable than D2 — a meta-analysis of 24 studies found D3 raises 25(OH)D by 15.69 nmol/L more than D2. SACN recommends 10 mcg daily for all UK adults year-round.
Strong evidence for bone health when combined with calcium (6% fracture reduction, 16% hip fracture reduction across 6 trials, n=49,282). Vitamin D alone does not prevent fractures. Modest immune benefit: meta-analysis of 43 RCTs confirms reduced acute respiratory infections (OR 0.92). The VITAL trial (n=25,871, 2,000 IU/day, 5.3 years) found no reduction in cancer incidence or CVD events, but a 25% reduction in cancer deaths after excluding the first 2 years. NHS recommends supplementation for all UK adults in autumn/winter.
Bone Health & Fracture Risk
6 studies · 49,282 participants
Serum 25(OH)D Correction
24 studies · 3,600 participants
Acute Respiratory Infections
43 studies · 48,488 participants
What the evidence shows
Research indicates Vitamin D3's role in bone health is well-established, with emerging evidence for immune function and potential benefits in reducing cancer mortality and depressive symptoms, though some areas require further robust investigation.
Vitamin D3 supplementation showed protective effects on bone mineral density at the lumbar spine, femoral neck, and total hip.
Kazemian et al. 2023, meta-analysis
Strong evidence indicates vitamin D3 supplementation reduced total cancer mortality (OR 0.90; 95% CI 0.87–0.92).
Petrelli et al. 2024, systematic-review
Vitamin D exerts dual immunological effects: enhancing innate immunity via upregulation of antimicrobial peptides while promoting immune tolerance by shifting T-helper balance toward anti-inflammatory Th2 responses.
Athanassiou et al. 2022, systematic-review
Vitamin D supplementation safely reduced the risk of acute respiratory infections overall, with greatest protection observed with daily doses of 400–1,000 IU for up to 12 months in children aged 1–16 years.
Jolliffe et al. 2021, meta-analysis
Vitamin D supplementation at 2,000 IU/day or above appears to reduce depressive symptoms in adults, with stronger effects in those diagnosed with major depressive disorder, though overall evidence certainty was rated very low.
Mikola et al. 2023, meta-analysis
The Evidence
14 peer-reviewed papers, updated 3 weeks ago
7 meta-analyses · 3 systematic reviews · 2 RCTs · 2 regulatory documents
Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines
Grant WB, Wimalawansa SJ, Pludowski P et al.
Nutrients
Serum 25(OH)D above 30 ng/mL substantially reduces risks of multiple diseases and mortality compared to levels below 20 ng/mL. The authors recommend daily supplementation of 2,000 IU for general disease prevention and 4,000–6,000 IU to achieve optimal protective serum levels of 40–70 ng/mL.
Vitamin D — Health Professional Fact Sheet
NIH Office of Dietary Supplements
NIH Office of Dietary Supplements
The NIH ODS recommends an RDA of 600 IU/day (ages 1–70) and 800 IU/day (>70 years), with a UL of 4,000 IU/day for adults. Serum 25(OH)D below 30 nmol/L indicates deficiency; 50 nmol/L is considered adequate. Consistent evidence supports bone health benefits; evidence for cancer, CVD, and other outcomes remains inconclusive.
Vitamin D3 and cancer risk in healthy subjects: An umbrella review of systematic review and meta-analysis
Petrelli F, Deda R, Borgonovo K et al.
Clinical Nutrition ESPEN
Strong evidence indicates vitamin D3 supplementation reduced total cancer mortality (OR 0.90; 95% CI 0.87–0.92). Sufficient vitamin D3 status was associated with potential prevention of head and neck, breast, colorectal, lung, renal cell, and thyroid cancers, supporting routine vitamin D assessment in preventive healthcare.
Scientific opinion on the tolerable upper intake level for vitamin D, including the derivation of a conversion factor for calcidiol monohydrate
Turck D, Bohn T, Castenmiller J et al.
EFSA Journal
The EFSA NDA Panel maintains a tolerable upper intake level of 100 µg/day (4,000 IU) vitamin D equivalents for adults and adolescents, with persistent hypercalciuria as the critical adverse effect. A conversion factor of 2.5 is established for calcidiol monohydrate labelling purposes.
Vitamin D supplementation and major cardiovascular events: D-Health randomised controlled trial
Thompson B, Waterhouse M, English DR et al.
BMJ
Monthly high-dose vitamin D3 (60,000 IU) was associated with a modest reduction in major cardiovascular events (HR 0.91) versus placebo in older adults, driven primarily by lower rates of myocardial infarction and coronary revascularisation. The absolute risk difference was small and confidence intervals were consistent with a null finding.
Vitamin D Supplementation and Its Impact on Mortality and Cardiovascular Outcomes: Systematic Review and Meta-Analysis of 80 Randomized Clinical Trials
Ruiz-Garcia A, Pallares-Carratala V, Turegano-Yedro M et al.
Nutrients
Across 80 RCTs, vitamin D supplementation was associated with a modest reduction in all-cause mortality (OR 0.95) but showed no statistically significant reduction in cardiovascular-specific mortality or morbidity. The authors conclude that further high-quality trials are required before firm clinical recommendations can be made.
Global and regional prevalence of vitamin D deficiency in population-based studies from 2000 to 2022: A pooled analysis of 7.9 million participants
Cui A, Zhang T, Xiao P et al.
Frontiers in Nutrition
Globally, 15.7% of people had severe vitamin D deficiency (25(OH)D <30 nmol/L) and 47.9% had levels below 50 nmol/L. Deficiency was more prevalent in females, high-latitude regions, winter months, and lower-middle-income countries, indicating a substantial global public health burden requiring intervention.
Efficacy of vitamin D3 supplementation on cancer mortality: Systematic review and individual patient data meta-analysis of randomised controlled trials
Kuznia S, Zhu A, Akutsu T et al.
Ageing Research Reviews
Daily vitamin D3 supplementation reduced cancer mortality by 12% compared to placebo; bolus dosing showed no significant benefit. Subgroup analyses favoured adults aged 70 and older and those initiating supplementation before cancer diagnosis. The overall pooled effect across all 14 RCTs did not reach statistical significance.
Effect of supplemental vitamin D3 on bone mineral density: a systematic review and meta-analysis
Kazemian E, Pourali A, Sedaghat F et al.
Nutrition Reviews
Vitamin D3 supplementation showed protective effects on BMD at the lumbar spine, femoral neck, and total hip. Dose-response relationships varied by skeletal site; BMD at the forearm was not improved. Results support targeted supplementation for bone health but highlight the importance of site-specific assessment.
The effect of vitamin D supplementation on depressive symptoms in adults: A systematic review and meta-analysis of randomized controlled trials
Mikola T, Marx W, Lane MM et al.
Critical Reviews in Food Science and Nutrition
Analysis of 41 RCTs (n=53,235) found that vitamin D supplementation at 2,000 IU/day or above appears to reduce depressive symptoms in adults, with stronger effects in those diagnosed with major depressive disorder. Overall evidence certainty was rated very low due to high heterogeneity and risk of bias.
Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults
LeBoff MS, Chou SH, Ratliff KA et al.
New England Journal of Medicine
Among 25,871 generally healthy adults not selected for vitamin D deficiency or osteoporosis, daily vitamin D3 2000 IU did not significantly reduce risk of total, non-vertebral, or hip fractures compared to placebo over a median 5.3 years of follow-up.
The Immunomodulatory Properties of Vitamin D
Athanassiou L, Mavragani CP, Koutsilieris M
Mediterranean Journal of Rheumatology
Vitamin D exerts dual immunological effects: enhancing innate immunity via upregulation of antimicrobial peptides (cathelicidin, defensins) while promoting immune tolerance by shifting T-helper balance toward anti-inflammatory Th2 responses. Deficiency is consistently associated with greater disease severity in autoimmune and inflammatory conditions.
Effect of Vitamin D Supplementation on Risk of Fractures and Falls According to Dosage and Interval: A Meta-Analysis
Kong SH, Jang HN, Kim JH et al.
Endocrinology and Metabolism
Daily vitamin D supplementation at 800–1,000 IU was associated with significantly lower risks of osteoporotic fracture and falls. Higher or lower doses and intermittent dosing regimens did not demonstrate equivalent benefit. Patients with pre-existing vitamin D deficiency showed the greatest risk reduction for falls.
Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials
Jolliffe DA, Camargo CA Jr, Sluyter JD et al.
Lancet Diabetes & Endocrinology
Vitamin D supplementation safely reduced risk of acute respiratory infections overall (OR 0.92) across 46 RCTs with 75,541 participants. Greatest protection was observed with daily doses of 400–1,000 IU for up to 12 months in children aged 1–16 years. Bolus dosing provided no significant benefit.
Evidence Database
Click any row to explore the studies behind each health outcome. Grades reflect the volume and quality of published research, not a recommendation.
| Grade | Health Outcome | |
|---|---|---|
| A | Bone Health & Fracture Risk6 studies | |
| A | Serum 25(OH)D Correction24 studies | |
| B | Acute Respiratory Infections43 studies | |
| B | Cancer Mortality3 studies | |
| C | Depression & Mood20 studies |
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What it is
Vitamin D3 (cholecalciferol) is a fat-soluble secosteroid hormone vital for several bodily functions, including calcium absorption, bone mineralisation, and immune system regulation. In the UK, due to its northern latitude, the synthesis of vitamin D in the skin from sunlight is negligible during the autumn and winter months (October to March). National data indicates that a significant proportion of UK adults have insufficient vitamin D levels, with deficiency rates rising considerably in winter and among specific population groups, such as those with darker skin tones. Vitamin D3 is generally considered more effective at raising and maintaining blood vitamin D levels compared to vitamin D2. The Scientific Advisory Committee on Nutrition (SACN) recommends a daily intake of 10 micrograms (400 International Units) of vitamin D for all UK adults year-round.
How it works
Vitamin D, once absorbed or synthesised, is metabolised into its active form, calcitriol. This active form plays a crucial role in regulating calcium and phosphate levels in the body, which are essential for maintaining healthy bones and teeth. It facilitates the absorption of calcium from the gut and its deposition into bone tissue. Beyond bone health, vitamin D also has significant immunomodulatory properties. It enhances innate immunity by upregulating antimicrobial peptides, such as cathelicidin, which help the body fight off infections. Simultaneously, it promotes immune tolerance by influencing the balance of T-helper cells towards anti-inflammatory responses, which can be beneficial in managing inflammatory conditions.
General Information
Dosage (Evidence-Reported)
These figures reflect what clinical studies used — not personalised recommendations.
Safety Notes
- Toxicity at serum 25(OH)D >375 nmol/L — almost always from supplement overuse, not sun
- Primary toxicity risk is hypercalcaemia: nausea, vomiting, kidney stones, cardiac arrhythmias
- Do not exceed 100 mcg (4,000 IU)/day without medical supervision
- 7 major drug interactions — notably thiazide diuretics, digoxin, and antiepileptic drugs
- Vitamin D alone (without calcium) shows no fracture protection in RCTs
- Contraindicated in hypercalcaemia, sarcoidosis, and severe renal impairment
Key Benefits
- Essential for calcium absorption and bone mineralisation — prevents rickets and osteomalacia
- Supports innate immunity via cathelicidin and defensin upregulation
- Modestly reduces acute respiratory infection risk (Lancet D&E, 43 RCTs)
- May reduce cancer mortality by 12–13% (3 meta-analyses, not incidence)
- Reduces depressive symptoms (SMD: −0.36, 20 RCTs) — stronger for short-term use
- Associated with 1.42x lower dementia risk when sufficient (23 prospective studies)
Quick Facts
Legal food supplement (UK). No prescription required. EFSA authorised health claim: contributes to normal absorption/utilisation of calcium and phosphorus, normal blood calcium levels, maintenance of normal bones, muscle function, teeth, and immune system function. SACN 10 mcg/day recommendation for all UK adults.
Frequently Asked Questions
Nutripedia is an educational resource. Content is sourced from peer-reviewed studies and does not constitute medical advice. Consult a healthcare professional before starting any supplement.