Effect of moderate or high versus low dose daily vitamin D on COVID-19 incidence: A double-blind, parallel-group randomized clinical trial

Meltzer et al., Clinical Nutrition, doi:10.1016/j.clnu.2026.106722 (results released 12/10/2025), NCT04868903, Dec 2025
ProphylaxisRCT · 1,475 patients · USA · Dec 2020 – May 2023
Vitamin D for COVID-19
Meltzer et al. Clinical Nutrition · December 2025 · NCT04868903
Fewer cases and symptomatic cases
Not statistically significant · p = 0.091 (Fewer cases) and p = 0.06 (symptomatic cases)

Vitamin D for COVID-19

8th treatment shown to reduce risk in October 2020, now with p < 0.0000000001 from 138 studies, recognized in 18 countries.
Lower risk for mortality, ICU, hospitalization, progression, recovery, cases, and viral clearance.

No treatment is 100% effective.
Protocols combine treatments.

6,700+ studies · 220+ treatments

c19early.org
Meta-analysis
RCT 923 adults in the USA showing lower COVID-19 incidence with 4,000 IU/day vitamin D compared with 400 IU/day (aHR 0.62, p=0.045), but no significant benefit with 10,000 IU/day (aHR 0.99). The prespecified pooled comparison of 4,000/10,000 IU/day versus 400 IU/day was not significant (aHR 0.73, p=0.10) - combining the two arms diluted the efficacy seen with 4,000 IU. The 4,000 IU benefit is consistent in magnitude across time-varying models (aHR 0.52-0.54), the fully immunized subgroup (0.56, p=0.021), and the post-registration subset. Notably, participants were largely replete at baseline (mean 35.9 ng/mL) so this is not a deficiency-correction finding.
Results are consistent with the a priori expectation of efficacy at 4,000 IU but worse results with 10,000 IU, although the paper's pooling of these arms results in a loss of significance.
A priori, 4,000 IU/day is expected to be the most effective of the doses tested. 400 IU is below the RDA and raises 25(OH)D by ~5 ng/mL, not enough to move many deficient people to sufficiency. The IOM/National Academies UL for adults is 4,000 IU/day which reliably produces levels in the 40-50 ng/mL range without a hypercalcemia signal. 10,000 IU is 2.5x the UL, and several mechanisms may produce worse results with excessive dosage:
CYP24A1 induction - high vitamin D exposure activates feedback degradation pathways, reducing effective VDR signaling.
FGF23 elevation - chronic high intake suppresses CYP27B1-mediated activation of vitamin D and promotes CYP24A1-mediated catabolism.
Metabolic resistance - chronic excessive exposure may induce compensatory responses beyond the above (PTH suppression reducing CYP27B1 activity, CYP2R1 downregulation limiting 25-hydroxylation, CYP3A4-mediated catabolism, C3-epimerization, and VDR-level desensitization), reducing effective intracellular signaling.
Immune over-tolerization - excessive VDR activation may promote regulatory and anti-inflammatory immune states at the potential cost of reduced pathogen clearance.
Susceptible subpopulations - potential increased harm for susceptible subpopulations including CYP24A1 or SLC34A1 loss-of-function carriers, granulomatous disease, and primary hyperparathyroidism.
Calcium/phosphate dysregulation - excess downstream mineral effects can create adverse outcomes.
VDR-independent off-target effects - at very high concentrations, lipid-soluble vitamin D metabolites may lose receptor specificity and trigger non-canonical pathways, cellular toxicity, and oxidative stress.
Skeletal remodeling effects - excess calcitriol signaling may increase RANKL-mediated osteoclast activity and suppress PTH-dependent remodeling, potentially contributing to bone loss.
Authors make incorrect claims in the abstract and conclusion:
They claim "moderate or high versus low dose vitamin D supplementation did not decrease COVID-19 risk" - however moderate dose and both arms pooled show lower risk, and statistical significance was reached for the moderate dose. Authors could say: "results matched a priori expectations with significantly lower COVID-19 incidence for 4,000 IU and no significant difference for 10,000 IU".
They claim "COVID-19 was not reported less for pooled moderate or high versus low dose" - aOR 0.37 and aOR 0.62 are both less. Authors could say: "among seroconverting patients, symptomatic COVID-19 was reported less for pooled moderate or high versus low dose and moderate versus low dose, without reaching statistical significance."
The terminology in the discussion is more accurate, however the conclusion repeats an incorrect statement.
This is the 40th of 41 COVID-19 RCTs for vitamin D, which collectively show efficacy with p=0.00000049.
This is the 135th of 138 COVID-19 controlled studies for vitamin D, which collectively show efficacy with p<0.0000000001.
Standard of Care (SOC) for COVID-19 in the study country, the USA, is very poor with very low average efficacy for approved treatments1. Only expensive, high-profit treatments were approved for early treatment. Low-cost treatments were excluded, reducing the probability of early treatment due to access and cost barriers, and eliminating complementary and synergistic benefits seen with many low-cost treatments.
Important missing comments or errors? Let us know.
risk of case, 27.0% lower, HR 0.73, p = 0.09, treatment 461, control 462, adjusted per study, 4,000 IU and 10,000 IU vs. 400 IU, multivariable, Cox proportional hazards.
risk of case, 38.0% lower, HR 0.62, p = 0.04, treatment 299, control 300, adjusted per study, 4,000 IU vs. 400 IU, multivariable, Cox proportional hazards.
risk of case, 1.0% lower, HR 0.99, p = 0.98, treatment 162, control 162, adjusted per study, 10,000 IU vs. 400 IU, multivariable, Cox proportional hazards.
risk of symptomatic case, 63.0% lower, OR 0.37, p = 0.06, treatment 36, control 50, symptomatic COVID-19 among seroconverters, 4,000 IU vs. 400 IU, RR approximated with OR.
risk of symptomatic case, 38.0% lower, OR 0.62, p = 0.26, treatment 58, control 72, symptomatic COVID-19 among seroconverters, pooled 4,000 IU and 10,000 IU vs 400 IU, RR approximated with OR.
Effect extraction follows pre-specified rules prioritizing more serious outcomes. Submit updates
Meltzer et al., 10 Dec 2025, Double Blind Randomized Controlled Trial, USA, peer-reviewed, 11 authors, study period 5 December, 2020 - 23 May, 2023, dosage 4,000IU daily, trial NCT04868903 (history). Contact: dmeltzer@bsd.uchicago.edu.
$0 $500 $1,000+ Efficacy vs. cost for COVID-19 treatment protocols c19early.org October 2026 USA Angola Colombia Kenya Mozambique Myanmar South Africa Peru Philippines Vietnam Japan Argentina Nepal Iran Bangladesh Ethiopia Ghana Germany Mexico South Korea United Kingdom Saudi Arabia Algeria Morocco Yemen Poland Uzbekistan India China Venezuela DR Congo Madagascar Thailand Uganda Egypt Nigeria Taiwan Fiji Zambia Bosnia-Herzegovina Jordan Georgia Switzerland Dominican Republic Bolivia Côte d'Ivoire Eritrea Togo Bulgaria Greece Slovakia Iceland New Zealand Trinidad and Tobago Mongolia Czechia Belarus Israel Haiti North Macedonia Hong Kong Qatar Panama Serbia USA favored high-profit treatments.The average efficacy of treatments was very low.High-cost protocols reduce early treatment, andforgo complementary/synergistic benefits. More effective More expensive 75% 50% 25% ≤0%
$0 $500 $1,000+ Efficacy vs. cost for COVID-19treatment protocols worldwide c19early.org October 2026 USA Angola Colombia Kenya Mozambique Myanmar South Africa Peru Philippines Vietnam Japan Argentina Nepal Iran Bangladesh Ethiopia Ghana Germany Mexico South Korea United Kingdom Saudi Arabia Algeria Morocco Yemen Poland Uzbekistan India China Venezuela DR Congo Madagascar Thailand Uganda Egypt Taiwan Fiji Zambia Jordan Georgia Switzerland Dominican Rep. Bolivia Côte d'Ivoire Eritrea Togo Sri Lanka Bulgaria Greece Slovakia New Zealand Trinidad and Tobago Mongolia Czechia Belarus Israel North Macedonia Hong Kong Qatar Panama Serbia USA favored high-profit treatments.The average efficacy was very low.High-cost protocols reduce early treatment,and forgo complementary/synergistic benefits. More effective More expensive 75% 50% 25% ≤0%
Abstract: HHS Public Access Author manuscript Clin Nutr. Author manuscript; available in PMC 2026 July 23. Published in final edited form as: Clin Nutr. ; 64: 106722. doi:10.1016/j.clnu.2026.106722. Effect of moderate or high versus low dose daily vitamin D on COVID-19 incidence: a double-blind, parallel-group randomized clinical trial David O. Meltzer, MD, PhD a,* , James N. Moy, MD b , Andrew W. Schram, MD, MBA a , Alexandra Tate, PhD a , Max J. Hyman, BA a , John F. Cursio, PhD c , Tamara Vokes, MD a , Kiang-Teck J. Yeo, PhD d , Micah Prochaska, MD, MSc a , Joshua J. Jacobs, MD e , Julian Solway, MD a a Department of Medicine, The University of Chicago, Chicago, IL, USA b Department of Internal Medicine, Rush Medical College, Chicago, IL, USA c Department of Public Health Sciences, The University of Chicago, Chicago, IL, USA d Department of Pathology, The University of Chicago, Chicago, IL, USA e Department of Orthopaedic Surgery, Rush Medical College, Chicago, IL, USA Abstract Background &amp; aims: Vitamin D affects immune function and is associated with lower COVID-19 risk in observational studies. However, randomized clinical trials vary in whether they find vitamin D supplementation affects COVID-19 risk. The objective of this trial was to determine whether moderate or high dose vitamin D (4,000 or 10,000 IU/day) versus low dose vitamin D (400 IU/day) affects COVID-19 risk. Methods: We conducted a double-blind, parallel-group randomized trial (clinicaltrials.gov, NCT0486890) enrolling participants from December 5, 2020 to May 23, 2023 who chose between * Corresponding Author (dmeltzer@bsd.uchicago.edu). Author contributions James N. Moy: Conceptualization, Investigation, Project Administration, Resources, Supervision, Writing - Review &amp; Editing. Andrew W. Schram: Investigation, Project Administration, Supervision, Writing - Review &amp; Editing. David O. Meltzer: Conceptualization, Data Curation, Formal Analysis, Funding Acquisition, Investigation, Methodology, Project Administration, Resources, Software, Supervision, Validation, Visualization, Writing - Original Draft Preparation, Writing - Review &amp; Editing. Alexandra Tate: Investigation, Project Administration, Supervision, Writing - Review &amp; Editing. John F. Cursio: Formal Analysis, Methodology, Software, Writing - Review &amp; Editing. Max J. Hyman: Data Curation, Formal Analysis, Methodology, Software, Validation, Visualization, Writing - Original Draft Preparation, Writing - Review &amp; Editing. Tamara Vokes: Investigation, Writing - Review &amp; Editing. Micah Prochaska: Investigation, Project Administration, Writing - Review &amp; Editing. Kiang-Teck J. Yeo: Resources, Writing - Review &amp; Editing. Joshua J. Jacobs: Funding Acquisition, Investigation, Writing - Review &amp; Editing. Julian Solway: Funding Acquisition, Investigation, Writing - Review &amp; Editing. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Competing interests The authors have declared that no competing interests exist. study branches..
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Please send us corrections, updates, or comments. c19early involves the extraction of 200,000+ datapoints from thousands of papers. Community updates help ensure high accuracy. Treatments and other interventions are complementary. All practical, effective, and safe means should be used based on risk/benefit analysis. No treatment or intervention is 100% available and effective for all current and future variants. We do not provide medical advice. Before taking any medication, consult a qualified physician who can provide personalized advice and details of risks and benefits based on your medical history and situation. IMA and WCH provide treatment protocols.
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