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Reviewed by the Scan Dose Research Team and Clinical Advisory Board

Vitamin D

STRONG EVIDENCEVitaminLast updated April 5, 2026

SCAN DOSE SUMMARY

Vitamin D is a fat-soluble vitamin that our skin produces from sunlight — but most people don't make enough, especially in winter or with indoor lifestyles. Our research, drawing from 97 RCTs, 38 meta-analyses, and over 1.1 million participants, confirms it supports bone health, immune function, and mood. Deficiency is widespread and linked to increased infection risk, depression, and bone disorders. Vitamin D3 is the recommended supplemental form, as it raises blood levels more effectively than D2.

EVIDENCE GRADES

C-Reactive Protein (CRP) reductionStrong
A
Bone Mineral DensityStrong
A
Fracture Risk ReductionStrong
A
Plasma Vitamin D increaseStrong
A
Parathyroid Hormone regulationModerate
B
Influenza RiskModerate — 2 studies, 2,003 participants
B
Depression SymptomsModerate
B
Blood PressureModerate
B
Insulin SensitivityModerate
B
Upper Respiratory Infection RiskLimited — 15 studies, 18,909 participants, small improvement
C

WHAT IT DOES

  • Supports bone health — Grade A evidence. Essential for calcium absorption and bone mineralization. Prevents rickets and osteomalacia.
  • Reduces inflammation — Grade A evidence for CRP reduction across multiple conditions.
  • Supports immune function — Moderate evidence for reducing influenza and upper respiratory infections, especially in deficient populations.
  • May improve mood/depression — Grade B evidence, particularly in people with low baseline vitamin D levels.
  • Supports metabolic health — Moderate evidence for improvements in insulin sensitivity, blood pressure, and lipid profiles.
  • Does NOT meaningfully improve: Muscle mass, muscle strength, multiple sclerosis symptoms (Grade D for these outcomes).

OPTIMAL DOSAGE

  • General maintenance: 1,000-2,000 IU (25-50 μg) per day for most adults
  • If deficient (blood levels <20 ng/mL): 4,000-5,000 IU daily for 8-12 weeks, then retest
  • RDA (adults 19-70): 600 IU (15 μg) per day — widely considered too low by many researchers
  • RDA (adults >70): 800 IU (20 μg) per day
  • Tolerable Upper Intake Level: 4,000 IU (100 μg) per day — doses up to 10,000 IU not associated with adverse events in studies
  • Best form: Vitamin D3 (cholecalciferol) — raises blood levels more effectively than D2 (ergocalciferol)
  • Timing: Take with a meal containing fat for better absorption (fat-soluble). Long-term, this matters less.
  • With food or empty stomach: With food preferred (fat improves absorption), but the difference is small over time.
  • Target blood level: 30-50 ng/mL (75-125 nmol/L) is generally considered optimal
Scan a supplement containing Vitamin D

DRUG INTERACTIONS

Calcium supplementsSevere

Enhances calcium absorption

Monitor calcium levels. Don't combine high-dose vitamin D with high-dose calcium without medical supervision.

Fish OilModerate

May raise HbA1c

Monitor HbA1c if diabetic and combining both supplements.

CYP3A4 substrate drugs (atorvastatin, sirolimus, tacrolimus, etc.)Minor

Reduces drug levels

Monitor drug efficacy. Effect appears clinically minor.

StrontiumUnknown

Increases strontium absorption

Relevance mainly for strontium ranelate users.

CYP3A4 substrate supplementsUnknown

Reduces supplement levels

Monitor if combining.

SAFETY PROFILE

Side Effects

  • At recommended doses (up to 4,000 IU/day): Well tolerated. Side effects not different from placebo in studies.
  • At excessive doses (50,000+ IU/day for weeks/months): Hypercalcemia (dangerously high calcium levels) → can progress to kidney stones, kidney insufficiency, soft tissue calcification
  • At extreme doses (600,000 IU injection): Kidney injury documented

Drug Interactions

Note on hypercalcemia-related interactions: Toxic levels of vitamin D (causing hypercalcemia) can reduce verapamil effectiveness, induce arrhythmia with digoxin, and worsen with thiazide diuretics. These interactions only occur at toxic doses — not normal supplementation.

Nutrient Depletions (Drugs That Deplete Vitamin D)

  • Antiepileptic drugs (phenobarbital, phenytoin, carbamazepine) — increase vitamin D metabolism, reduce levels, increase fracture risk. Monitor and supplement.
  • Efavirenz — associated with severe vitamin D deficiency
  • Aromatase inhibitors — reduce conversion to active form. May need higher doses (50,000 IU/week under medical supervision)
  • Orlistat — may reduce absorption of fat-soluble vitamins. Take vitamin D 2 hours before or after orlistat.
  • Antineoplastic drugs — associated with lower vitamin D levels
  • Bile acid sequestrants (cholestyramine, colestipol) — may reduce absorption. Take vitamin D 4+ hours before these drugs.

Precautions

  • Pregnancy: Safe. Up to 4,000 IU/day is the UL. Some studies used up to 100,000 IU with no adverse effects on offspring followed for up to 16 years.
  • Breastfeeding: Safe. 4,000 IU/day recommended by some researchers to provide adequate vitamin D to infant via breast milk.
  • Children: Safe at age-appropriate doses (400-1,000 IU depending on age).
  • Chronic kidney disease: Use with caution. People with CKD have difficulty converting vitamin D to its active form and are more likely to be deficient. Supplementation may increase calcium levels and arterial stiffness. Must be monitored by a healthcare provider.
  • Surgery: No specific concerns.

Quality Concerns

Studies show vitamin D supplement content frequently varies from label claims. Dose AI recommends third-party verified products.

WADA Status

Not Prohibited. Not on the 2026 WADA list.

WHO SHOULD BE CAREFUL

QUALITY CONCERNS

Studies show vitamin D supplement content frequently varies from label claims. Dose AI recommends third-party verified products.

HOW SCAN DOSE SCORES THIS

Present in proper dose (1,000-4,000 IU D3):✅ Green flag — essential vitamin, most people benefit from supplementation
Underdosed (<400 IU):⚠️ Yellow flag — below even the conservative RDA
D2 form instead of D3:⚠️ Yellow flag — less effective at raising blood levels
In a proprietary blend:⚠️ Yellow flag — impossible to verify if dose is meaningful
Above 10,000 IU daily without medical supervision:🔴 Red flag — increases hypercalcemia risk
Combined with very high calcium (>1,500mg):⚠️ Yellow flag — monitor for hypercalcemia risk

CLINICAL REFERENCES

1.

Vitamin D reduced risk of acute respiratory infection, with greatest benefit in those with low baseline levels and daily dosing.

Jolliffe DA et al. Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis.. Lancet Diabetes Endocrinol (2021). PMID: 36715304

2.

High-dose vitamin D (4,000 and 10,000 IU/day) for 3 years decreased bone density compared to 400 IU — showing more is NOT always better.

Burt LA et al. Effect of High-Dose Vitamin D Supplementation on Volumetric Bone Density and Bone Strength.. JAMA (2019). PMID: 31405774

3.

Vitamin D supplementation did not significantly reduce risk of cardiovascular disease, cancer, or fractures in vitamin D-sufficient populations.

Autier P et al. Effect of vitamin D supplementation on non-skeletal disorders: a systematic review.. Lancet Diabetes Endocrinol (2017). PMID: 32365423

4.

Vitamin D deficiency is associated with depression, and supplementation may improve mood in deficient individuals.

Penckofer S et al. Vitamin D and Depression: Where is all the Sunshine?. Issues Ment Health Nurs (2010). PMID: 30918187

5.

Target 25(OH)D level of 30-50 ng/mL recommended. Deficiency (<20 ng/mL) requires 50,000 IU weekly for 6-8 weeks followed by maintenance.

Giustina A et al. Consensus statement on vitamin D status assessment and supplementation.. Eur J Endocrinol (2020). PMID: 34607398

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Quality Testing Intelligence

Based on independent third-party laboratory analysis

Category pass rate: ~90% pass rate. One notable failure: Biotics Research at 195% of label (nearly double).

Common failures:
Over-dosing: Biotics Research contained 195% of labeled vitamin D (7,798 IU instead of 4,000 IU)
Under-dosing in multivitamins: Garden of Life Women's Multi only 54.8% vitamin D
Form confusion: D2 (ergocalciferol) vs D3 (cholecalciferol) — D3 is preferred
Form comparison:
Form: Efficacy: Source: Notes
D3 (Cholecalciferol): HIGHEST: Lanolin (animal) or Lichen (vegan): Preferred form. 87% more potent than D2 at raising blood levels.
D2 (Ergocalciferol): LOWER: Mushrooms/yeast: 87% less effective at raising blood levels than D3.
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Reviewed by the Scan Dose Research Team and Clinical Advisory Board | Last updated: April 5, 2026

Not medical advice. Based on published clinical research and systematic reviews.

Safety

Vitamin D: Drug Interactions

Use with caution

Moderate interactions. Monitoring, timing separation, or dose adjustment may be required.

  • Thiazide diuretics (HCTZ)

    Thiazides reduce calcium excretion while vitamin D increases calcium absorption.

    RiskHypercalcemia.
    ActionMonitor serum calcium.

    Source: Clinical standard

  • Steroids (prednisone)

    Corticosteroids reduce vitamin D metabolism and calcium absorption.

    RiskAccelerated bone loss and vitamin D deficiency.
    ActionHigher vitamin D doses may be needed on long-term steroids.

    Source: Clinical standard

  • Orlistat (Alli)

    Reduces fat absorption, including fat-soluble vitamin D.

    RiskVitamin D deficiency.
    ActionSeparate by 2 or more hours. Monitor 25-OH vitamin D.

    Source: FDA label

  • Cholestyramine (bile acid sequestrant)

    Reduces vitamin D absorption.

    RiskDeficiency risk.
    ActionSeparate by 4 or more hours.

    Source: FDA label

Educational information only. This is not medical advice. These statements have not been evaluated by the FDA. Talk to your prescriber before starting, stopping, or combining any supplement with prescription medication.

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