Can vitamin d stop COVID-19? large trial tests high doses
NCT ID NCT04536298
First seen Jun 26, 2026 · Last updated Jun 26, 2026
Summary
This large study tested whether high-dose vitamin D3 supplements could help people recently diagnosed with COVID-19 avoid severe illness and also prevent the virus from spreading to their household members. Over 2,000 participants across the U.S. and Mongolia took either vitamin D or a placebo for 4 weeks. The goal was to see if vitamin D reduces healthcare visits and infections in close contacts.
What this could mean
Our plain-language read of the trial. This is informational only, not medical advice or a prediction.
- Active substance
- vitamin D3 (cholecalciferol) dietary supplement
- What this could lead to
- If it works, this could point toward a simple, low-cost way to reduce COVID-19 severity and prevent household spread.
- What could go wrong
- This is a completed Phase 3 trial, but vitamin D's effect on COVID-19 has been mixed in other studies. High doses may cause side effects like kidney stones.
This is an AI summary of the original study and may miss details. Read our disclaimer.
Study facts
What this study's own registry entry says, in plain language.
- Phase
-
Phase 3
Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.
- Participants
-
2,024 people
The number who actually took part.
- Started
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Dec 2020
- Finished
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Jul 2024
- Lead sponsor
-
Other sponsor
The registry's catch-all category, for sponsors it does not file as a company, a government agency, or a research network.
Who can take part
This study's own entry requirements. Only the study team can say for certain whether you qualify.
- Ages
-
18 years and older
- Sex
-
Anyone
- Healthy volunteers
-
Accepted
You do not need to have the condition being studied to take part.
Show the full entry requirements Hide the full entry requirements
Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.
Inclusion/exclusion criteria for INDEX CASES: Inclusion criteria 1. Adults aged 18 years or older who are newly diagnosed with COVID-19 infection within 7 days of testing. 2. Ability and willingness to understand and provide informed consent. Exclusion criteria 1. Known current pregnancy. 2. Current hospitalization. 3. Unable to complete online questionnaires or adhere to study requirements. 4. Consume more than 1000 IU per day of vitamin D from all supplemental sources combined (individual vitamin D supplements, calcium plus vitamin D supplements, medications with vitamin D \[e.g., Fosamax Plus D\], and multivitamins) in the past 4 weeks. 5. Use of prescription vitamin D treatments (Calcitriol \[Rocaltrol, Calcitrol, Vectical, Calcijex\] or Paricalcitol \[Zemplar\]). 6. Consume supplements with more than 1200 mg calcium per day. 7. Known diagnosis of hypercalcemia or a condition associated with vitamin D hypersensitivity. 8. Prior diagnosis of cancer \*AND\* currently undergoing radiation, chemotherapy, or immunotherapy. 9. Kidney failure or dialysis; severe liver disease or cirrhosis. 10. Any parathyroid conditions. 11. Use of medications for seizures or epilepsy. Examples: Carbamazepine (Carbatrol, Tegretol), Phenytoin (Dilantin, Phenytek), Valproic acid (Depakene), Oxcarbazepine (Oxtellar, Trileptal), Phenobarbital, Topiramate (Topamax). 12. Use of digoxin. 13. Inability to receive an overnight express mail shipment of study pills at a home address. 14. Participation in other COVID-19 trials. Inclusion/exclusion criteria for HOUSEHOLD CONTACTS: Inclusion criteria: 1. Persons aged 18 years or older who live in the same household with an index individual and have been identified as the closest household contact within the same household (limited to 1 per household). 2. Persons aged 18 years or older who live in household with someone who tested positive for COVID-19 within past 7 days but not participating in VIVID. 3. Ability and willingness to understand and provide informed consent. Exclusion criteria: 1. Known current pregnancy. 2. History of SARS-CoV-2 infection. 3. Receipt of a SARS-CoV-2 vaccination or monoclonal antibody. 4. Unable to complete online questionnaires or adhere to study requirements. 5. Consume more than 1000 IU per day of vitamin D from all supplemental sources combined (individual vitamin D supplements, calcium plus vitamin D supplements, medications with vitamin D \[e.g., Fosamax Plus D\], and multivitamins) in the past 4 weeks. 6. Use of prescription vitamin D treatments (Calcitriol \[Rocaltrol, Calcitrol, Vectical, Calcijex\] or Paricalcitol \[Zemplar\]). 7. Consume supplements with more than 1200 mg calcium per day. 8. Known diagnosis of hypercalcemia or a condition associated with vitamin D hypersensitivity. 9. Prior diagnosis of cancer \*AND\* currently undergoing radiation, chemotherapy, or immunotherapy. 10. Kidney failure or dialysis; severe liver disease or cirrhosis. 11. Any parathyroid condition. 12. Use of medications for seizures or epilepsy. Examples: Carbamazepine (Carbatrol, Tegretol), Phenytoin (Dilantin, Phenytek), Valproic acid (Depakene), Oxcarbazepine (Oxtellar, Trileptal), Phenobarbital, Topiramate (Topamax). 13. Use of digoxin. 14. Inability to receive an overnight express mail shipment of study pills at a home address. 15. Participation in other COVID-19 trials.
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Conditions
The condition(s) this trial relates to.
As listed by the trial registrant
The condition terms exactly as the trial's registrant entered them.
Contacts and locations
Locations
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Brigham and Women's Hospital
Boston, Massachusetts, 02215, United States
More trials for these conditions
Other studies related to the condition(s) this trial covers.
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- Can lung ultrasound reveal COVID-19's signature in the lungs?
- When the immune system Can't fight back: tracking three respiratory viruses
- The household maze: how does COVID-19 move between family members?
- Can an oral drug stop COVID-19 from turning deadly?
- Can COVID-19 rapid tests slip into HIV and TB clinics without disrupting care?