High-Dose Vitamin D3 Does Not Reduce Acute COVID-19 Severity But May Hold Promise for Long COVID

Long COVID-19 continues to burden US adults, with an estimated 17 million individuals currently experiencing long COVID, and roughly 8% of individuals report having ever faced the condition. Meanwhile, vitamin D deficiency remains highly prevalent in the US, with an overall deficiency rate of approximately 41.6% when defined as serum 25-hydroxyvitamin D [25(OH)D] concentrations of 20 ng/mL or less, with the highest rates among Black non-Hispanic and Hispanic adults.^1,2

Given the theoretical immunologic rationale for vitamin D in modulating infection severity, investigators have long sought to determine whether supplementation could meaningfully alter COVID-19 outcomes.^1-3

Trial Design and Methods

The parallel 2-group, double-blinded, cluster-randomized, placebo-controlled Vitamin D for COVID-19 (VIVID) trial (NCT04536298), published in The Journal of Nutrition, represents one of the largest and most rigorous randomized controlled trials to date evaluating this question. The trial enrolled adults in the US and Mongolia from December 2020 through September 2022, including participants with newly diagnosed SARS-CoV-2 infection (n = 1747) that were randomly assigned with up to 1 cohabiting household contact (n = 277) to receive either oral vitamin D₃ (cholecalciferol) supplementation, involving a loading dose of 9600 IU per day for 2 days followed by 3200 IU per day for 4 weeks, or placebo. The primary outcome was at least 1 health care visit, including hospitalization or death, within 4 weeks.^4,5

The trial population had a median age of 38 years and was 65.6% female, and nearly 45% of participants entering the study were already vitamin D deficient or insufficient (25(OH)D <20 ng/mL).⁵

Key Findings

Despite the high burden of vitamin D deficiency at baseline, the 4-week cumulative incidence of health care utilization did not differ significantly between the vitamin D₃ and placebo groups (28% vs 29%; OR, 0.97; 95% CI, 0.75-1.24). Similarly, no significant differences were found in disease severity scores or in new SARS-CoV-2 infections among household contacts.⁵

In the vitamin D group, approximately 21% of individuals reported at least 1 persistent symptom compared with 25% in the placebo group—a difference of borderline statistical significance (OR, 0.78; 95% CI, 0.59-1.03).^5,6

While not meeting conventional thresholds for significance, this trend is notable given the mechanistic plausibility, as vitamin D modulates both innate and adaptive immunity by enhancing antimicrobial defense mechanisms and reducing excessive inflammatory responses. These same anti-inflammatory pathways are implicated in the persistent cytokine dysregulation hypothesized to drive long COVID symptoms, such as fatigue, brain fog, and dyspnea.^5,6

Pharmacist Implications

Pharmacists are uniquely positioned to counsel patients on vitamin D supplementation in the context of COVID-19 and long COVID. Given the high prevalence of vitamin D deficiency in the US population, pharmacists conducting medication therapy management should routinely assess vitamin D status and reinforce the importance of screening.³

Since the VIVID trial used a high loading dose regimen that is not currently guideline-recommended for routine COVID-19 treatment, pharmacists should counsel patients that self-initiating high-dose vitamin D₃ supplementation based on this single trial is premature. No safety signals were observed in the VIVID trial at the doses tested, but supraphysiologic dosing carries a risk of toxicity and should be medically supervised.⁵

Additionally, as long COVID remains a condition with no approved pharmacologic treatments, pharmacists can play a pivotal role in helping patients navigate evidence-based supportive care strategies while setting realistic expectations about supplements whose efficacy data remain preliminary.

“There’s been tremendous interest in whether vitamin D supplements can be of benefit in COVID, and this is one of the largest and most rigorous randomized trials on the subject,” JoAnn Manson, MD, DrPH, senior author from the Mass General Brigham Department of Medicine, said in a news release. “While we didn’t find that high-dose vitamin D reduced COVID severity or hospitalizations, we observed a promising signal for long COVID that merits additional research.”⁷

REFERENCES

1. Long COVID household pulse survey. CDC. Updated March 21, 2024. Published March 16, 2026. https://www.cdc.gov/nchs/covid19/pulse/long-covid.htm

2. Tracking long COVID. CDC. Updated March 9, 2026. Accessed March 16, 2026. https://www.cdc.gov/long-covid/php/surveillance/index.html

3. Forrest K, Stuhldreher W. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011;31(1):48-54. doi:10.1016/j.nutres.2010.12.001

4. Vitamin D for COVID-19 Trial (VIVID). ClinicalTrials.gov. Updated September 24, 2025. Accessed March 16, 2026. https://clinicaltrials.gov/study/NCT04536298

5. Ganmaa D, Cook K, Khudyakov P, et al. A randomized trial of vitamin D supplementation and COVID-19 clinical outcomes and long COVID: the VIVID Trial. J Nutr. Published online March 12, 2026. doi:10.1016/j.tjnut.2026.101398

6. Caliman-Sturdza OA, Gheorghita RE, Soldanescu I. Vitamin D and COVID-19: clinical evidence and immunological insights. Life (Basel). 2025;15(5):733. doi:10.3390/life15050733

7. Trial finds vitamin D supplements don’t reduce covid severity but could reduce long COVID risk. News release. EurekAlert. March 12, 2026. Accessed March 16, 2026. https://www.eurekalert.org/news-releases/1119304