- We did not find enough, good-quality evidence to judge whether vitamin D is an effective or safe treatment for adults with COVID-19.
- We need more research on this topic. Future research should focus on well-designed studies with robust methods.
- We identified 21 studies on this topic that are ongoing. We will update this review when more evidence becomes available.
What is the link between vitamin D and COVID-19?
Some studies have shown that people who are in hospital with severe COVID-19 also have low levels of vitamin D (vitamin D deficiency). However, the risk factors for developing severe COVID-19 are the same as those for developing vitamin D deficiency, so it is difficult to tell if vitamin D deficiency itself is a risk factor for severe COVID-19. Risk factors include general ill-health, a poor diet, and pre-existing health conditions, such as diabetes, and liver and kidney disease.
Vitamin D is important for healthy bones, teeth and muscles. It helps to regulate blood sugar, the heart and blood vessels, and the lungs and airways. It also has a role in boosting the body’s immune system. These are areas affected by COVID-19, so giving vitamin D to people with COVID-19 might help them to recover more quickly or have the disease less severely.
What did we want to find out?
We wanted to find out the effects of giving vitamin D to adults with confirmed COVID-19 on the following:
- death from any cause;
- improvement or worsening of the patient’s condition;
- unwanted effects; and
- quality of life.
What did we do?
We searched for studies that assessed the use of vitamin D as a treatment for adults with confirmed COVID-19 compared with a placebo (sham treatment) or another treatment. Vitamin D could be given in any form and in any dose.
We compared and summarised their results, and rated our confidence in the evidence, based on factors such as study methods and sizes.
What did we find?
We found three studies with 356 participants. One study took place in Brazil, and the other two in Spain. Two studies had participants with severe COVID-19 and one had participants with mild COVID-19 or with no symptoms. All the participants tested positive for COVID-19 with a laboratory test called ‘PCR’, which is currently the most accurate test available.
The studies gave their participants different doses of vitamin D. They used different timings from each other, from one large dose in one study to several smaller doses over 14 days in another study. Only two studies said that their participants were vitamin D-deficient. The other study did not say anything about their participants’ vitamin D status.
Deaths from any cause
We do not know whether vitamin D helps to prevent death from COVID-19. Two studies (in participants with severe COVID-19) provided evidence about deaths from any cause. One reported no deaths in the 50 participants who had received vitamin D, but two deaths in the 26 participants who received the hospital’s usual COVID-19 treatment. The other study reported nine deaths in 119 participants who had been given vitamin D and six deaths in the 118 participants given placebo. These studies were too different from each other to allow us to draw any conclusions.
Vitamin D may reduce the need for patients to be put on a ventilator to help them breathe, but the evidence is uncertain. One study (in participants with severe COVID-19) reported that nine out of 119 participants given vitamin D had to be put on a ventilator and 17 out of 118 given a placebo needed a ventilator.
We do not know whether vitamin D causes unwanted effects. Only one study (in participants with severe COVID-19) reported data on unwanted effects in a way that we could use. It found that one participant out of 119 vomited shortly after being given vitamin D.
Quality of life
None of the studies reported quality of life.
What are the limitations of the evidence?
Our confidence in the evidence is very limited because the studies gave different doses of vitamin D at different times from each other, did not all report participants’ vitamin D status, and did not measure and record their results using consistent methods.
We found little evidence on unwanted effects and none on quality of life.
How up to date is this evidence?
The evidence is up to date to 11 March 2021.
There is currently insufficient evidence to determine the benefits and harms of vitamin D supplementation as a treatment of COVID-19. The evidence for the effectiveness of vitamin D supplementation for the treatment of COVID-19 is very uncertain. Moreover, we found only limited safety information, and were concerned about consistency in measurement and recording of these outcomes.
There was substantial clinical and methodological heterogeneity of included studies, mainly because of different supplementation strategies, formulations, vitamin D status of participants, and reported outcomes.
There is an urgent need for well-designed and adequately powered randomised controlled trials (RCTs) with an appropriate randomisation procedure, comparability of study arms and preferably double-blinding. We identified 21 ongoing and three completed studies without published results, which indicates that these needs will be addressed and that our findings are subject to change in the future. Due to the living approach of this work, we will update the review periodically.
The role of vitamin D supplementation as a treatment for COVID-19 has been a subject of considerable discussion. A thorough understanding of the current evidence regarding the effectiveness and safety of vitamin D supplementation for COVID-19 based on randomised controlled trials is required.
To assess whether vitamin D supplementation is effective and safe for the treatment of COVID-19 in comparison to an active comparator, placebo, or standard of care alone, and to maintain the currency of the evidence, using a living systematic review approach.
We searched the Cochrane COVID-19 Study Register, Web of Science and the WHO COVID-19 Global literature on coronavirus disease to identify completed and ongoing studies without language restrictions to 11 March 2021.
We followed standard Cochrane methodology. We included randomised controlled trials (RCTs) evaluating vitamin D supplementation for people with COVID-19, irrespective of disease severity, age, gender or ethnicity.
We excluded studies investigating preventive effects, or studies including populations with other coronavirus diseases (severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS)).
We followed standard Cochrane methodology.
To assess bias in included studies, we used the Cochrane risk of bias tool (ROB 2) for RCTs. We rated the certainty of evidence using the GRADE approach for the following prioritised outcome categories: individuals with moderate or severe COVID-19: all-cause mortality, clinical status, quality of life, adverse events, serious adverse events, and for individuals with asymptomatic or mild disease: all-cause mortality, development of severe clinical COVID-19 symptoms, quality of life, adverse events, serious adverse events.
We identified three RCTs with 356 participants, of whom 183 received vitamin D. In accordance with the World Health Organization (WHO) clinical progression scale, two studies investigated participants with moderate or severe disease, and one study individuals with mild or asymptomatic disease. The control groups consisted of placebo treatment or standard of care alone.
Effectiveness of vitamin D supplementation for people with COVID-19 and moderate to severe disease
We included two studies with 313 participants. Due to substantial clinical and methodological diversity of both studies, we were not able to pool data. Vitamin D status was unknown in one study, whereas the other study reported data for vitamin D deficient participants. One study administered multiple doses of oral calcifediol at days 1, 3 and 7, whereas the other study gave a single high dose of oral cholecalciferol at baseline. We assessed one study with low risk of bias for effectiveness outcomes, and the other with some concerns about randomisation and selective reporting.
All-cause mortality at hospital discharge (313 participants)
We found two studies reporting data for this outcome. One study reported no deaths when treated with vitamin D out of 50 participants, compared to two deaths out of 26 participants in the control group (Risk ratio (RR) 0.11, 95% confidence interval (CI) 0.01 to 2.13). The other study reported nine deaths out of 119 individuals in the vitamin D group, whereas six participants out of 118 died in the placebo group (RR 1.49, 95% CI 0.55 to 4.04]. We are very uncertain whether vitamin D has an effect on all-cause mortality at hospital discharge (very low-certainty evidence).
Clinical status assessed by the need for invasive mechanical ventilation (237 participants)
We found one study reporting data for this outcome. Nine out of 119 participants needed invasive mechanical ventilation when treated with vitamin D, compared to 17 out of 118 participants in the placebo group (RR 0.52, 95% CI 0.24 to 1.13). Vitamin D supplementation may decrease need for invasive mechanical ventilation, but the evidence is uncertain (low-certainty evidence).
Quality of life
We did not find data for quality of life.
Safety of vitamin D supplementation for people with COVID-19 and moderate to severe disease
We did not include data from one study, because assessment of serious adverse events was not described and we are concerned that data might have been inconsistently measured. This study reported vomiting in one out of 119 participants immediately after vitamin D intake (RR 2.98, 95% CI 0.12 to 72.30). We are very uncertain whether vitamin D supplementation is associated with higher risk for adverse events (very low-certainty).
Effectiveness and safety of vitamin D supplementation for people with COVID-19 and asymptomatic or mild disease
We found one study including 40 individuals, which did not report our prioritised outcomes, but instead data for viral clearance, inflammatory markers, and vitamin D serum levels. The authors reported no events of hypercalcaemia, but recording and assessment of further adverse events remains unclear. Authors administered oral cholecalciferol in daily doses for at least 14 days, and continued with weekly doses if vitamin D blood levels were > 50 ng/mL.