Each month, we parse thousands of new studies to select the most important, review them, and summarize them for our Examine Members. Unsurprisingly, we ended up reviewing a good number of COVID-19 studies. The most studied supplement in the context of this disease is vitamin D. The present article is a short report on landmark studies on COVID-19 and vitamin D published between July 2020 and April 2021.
The takeaway
While there isn’t clear evidence that vitamin D helps fight off COVID-19, this disease does seem less severe in people with adequate vitamin D levels. The benefits of vitamin D are plausible, but keep in mind that, in the past, mechanistic and observational evidence in favor of vitamin D was not always confirmed in clinical trials.[1] Still, one thing is clear:
VITAMIN D IS NOT A REPLACEMENT FOR AN APPROVED COVID-19 VACCINE.

Vitamin D supplementation
A pilot randomized controlled trial found that ICU admission was needed by 50% of the COVID-19 patients not taking vitamin D, but by only 2% of those taking vitamin D.
A cohort study found that COVID-19 patients taking a supplement containing 150 mg of magnesium, 500 μg of B12, and 25 μg (1,000 IU) of D3 were less likely to require supplemental oxygen or ICU support than a control group.
A randomized controlled trial found a lack of benefit of 200,000 IU of vitamin D for those hospitalized due to COVID-19. (This study can’t rule out that vitamin D supplementation could have a preventive effect.)
In a randomized controlled trial, participants with mild or asymptomatic SARS-CoV-2 infections and vitamin d deficiency took placebo or 60,000 IU of vitamin D daily for 7 days, then the same dose for another 7 days, or a single dose if levels were high. The participants who took vitamin D had a notably shorter duration of SARS-CoV-2 infection.
In a retrospective cohort study, participants who received and 80,000 IU intravenous dose one month prior to infection or up to one week after infection were less likely to die than those who didn’t, though all participants received such doses regularly and their vitamin D status wasn’t known.
In a retrospective cohort study, the participants who had been receiving intravenous vitamin D every 2–3 months for the preceding year, but not the participants who received 80,000 IU of oral vitamin D within a few hours of COVID-19 diagnosis, were less likely to develop severe COVID-19 or die than those who had received no vitamin D.
In a retrospective cohort study, people with COVID-19 who received vitamin D upon hospitalization were less likely to die than those who didn’t.
In a prospective cohort study, people who survived were more likely to have been taking vitamin D than those who didn’t.
In a retrospective cohort study of participants with advanced chronic kidney disease, those who had received calcitriol were less likely to develop severe COVID-19 or die than those who didn’t.
Clinical evidence for vitamin D’s benefits is still very preliminary. Typically, many good studies need to be analyzed together for us to be confident that a supplement works. The results of the pilot study look very impressive, but the negative study casts doubt, and the observational studies have significant weaknesses and potential for confounding and bias. We need more good quality trials that provide data in different patient contexts to understand how supplementation can be useful.
Vitamin D levels
A meta-analysis associated vitamin D levels under 30 ng/mL with a 43% increase in odds of COVID-19 infection.
A systematic review and meta-analysis found that, while vitamin D deficiency was not associated with the risk of COVID-19 infection, people who had COVID-19 had lower vitamin D levels than those who did not have COVID-19.
One systematic review found that COVID-19 patients with a poor prognosis had lower levels of vitamin D than those with a good prognosis.
A retrospective cohort study found that people with vitamin D deficiency were more likely to die from COVID-19.
A restrospective cohort study found that vitamin D levels over 40 ng/ml may be the most protective for Black people, whereas level didn't seem to matter for White people.
A retrospective cohort study found a strong, inverse correlation between vitamin D levels and COVID-19 infection rate.
A retrospective cohort study associated higher vitamin D levels with lower mortality: ≥30 ng/mL (≥75 nmol/L) with 9.2% mortality; <30 ng/mL with 25.3% mortality.
Overall, lower vitamin D levels seem correlated with a higher risk of COVID-19 and its complications, but one of the meta-analyses casts some doubt on this. It’s also possible that people with lower vitamin D levels are more susceptible due to worse general nutrition, a higher rate of comorbidities, a higher level of systemic inflammation, or other confounding factors. We’ll learn more in the next few months as we keep reviewing and summarizing studies on this topic for our Members.
Mechanisms
A review reported a notable correlation between lower vitamin D levels and both COVID-19 infection rate and poor COVID-19 outcomes. It hypothesized that vitamin D might reduce the risk of COVID-19 infection and death by improving innate immunity, maintaining cell junctions, modifying gene expression, and acting as an antimicrobial.
A narrative review reported that vitamin D supplementation may benefit patients with COVID-19 by reducing the macrophage-driven hyperinflammatory response in the lungs.
It’s very clear that vitamin D plays a significant role in immune function and regulation, but it’s not so clear how low vitamin D levels need to be for this to be relevant to COVID-19.
General nutrition for COVID-19
A narrative review associated vitamin D deficiency or insufficiency with worse COVID-19 outcomes. It also found that vitamin D supplements enhanced the immune response to COVID when combined with high-dose vitamin C. (But a five-day open-label randomized controlled trial found that high-dose intravenous vitamin C was unlikely to improve COVID-19 outcomes.)
Stay on top of the latest research
Our Examine Membership makes it easy for you to stay on top of the latest research. This article links to just a few our summaries — we publish over 150 across 25 health topics every month.
Try out an Examine Membership for free for 14 days. »
💊 Get unbiased supplement information
Related Articles
- 5 nutrients that could lift your mood
- Can supplemental vitamin D improve sleep?
- Should 1000 IU be the new RDA for vitamin D?
- When should I take Vitamin D?
- Can vitamin D-crease pain?
- Can vitamin D cure depression?
- How can you increase testosterone naturally?
- How much fat do I need to absorb vitamin D?
- Does sunscreen decrease vitamin D?
- Do I need to supplement Vitamin D if I drink fortified milk?
- Do B vitamins increase the risk of getting cancer?
- Does aspartame cause headaches?
- Why do my muscles get sore?
- Is saturated fat bad for your health?
- Does chewing gum offer any health benefits?
- How do I calculate my metabolism?
- Can creatine cause cancer?
- Do artificial sweeteners spike insulin?
- Fact check: does glutamine build muscle?
- Are nitrates from beetroot and processed meats the same thing?
- How do I stay out of "starvation mode?"
- Does creatine benefit elite athletes?
- Is my “slow metabolism” stalling my weight loss?
- Is creatine safe for your kidneys?
- Does eating at night make it more likely to gain weight?
- Is it better to do aerobic exercise fasted?
- Why you shouldn't be always taking antioxidants, especially if you want to build muscle
- Does “low-carb” have an official definition?
- How do I increase insulin sensitivity?
- Does diet soda inhibit fat loss?
- Does vinegar increase metabolism?
- What are the benefits of resistance training?
- Can drinking wine really replace exercise?
- Do you need to detox?
- Can one binge make you fat?
- Can you lose weight by turning down the heater?
- Does creatine cause hair loss?
- Will carbs make me fat?
- How can you assess protein quality?
- Are natural sunscreens effective?
- Does daily weighing help you lose weight?
- How do I get a six-pack?
- What supplement or food changes are recommended for pregnant or expecting women?
- Do herbal aphrodisiacs work?
- Can you be Healthy and Obese?
- Does ashwagandha increase testosterone?
- Can creatine increase your testosterone levels?
- Do I need to cycle ephedrine?
- How does protein affect weight loss?
- Does dairy cause acne?
- Are vitamin C supplements bad for your teeth?
- What should you eat for weight loss?
- Can eating too much protein be bad for you?
- Which supplements can help against colds and the flu?
- Can food have negative calories?
- Which grocery items are affordable and healthy?
- Do I need to load creatine?
- Does vitamin C improve blood sugar control?
- Will eating eggs increase my cholesterol?
- Do I need to cycle caffeine?
- Can autism be helped by gluten-free, casein-free diets?
- Does red meat cause cancer?
- Will lifting weights convert my fat into muscle?
- Does ZMA cause weird dreams?
- Does caffeine counteract creatine?
- How are carbohydrates converted into fat deposits?
- Does eating fat make you fat?
- Is diet soda bad for you?
- How does caffeine work in your brain?
- How important is sleep?
- Is processed meat bad for me?
- Should you supplement with vitamin K?
- What is Adrenal Fatigue?
- Are energy drinks bad for you?
- Does resistance training work for the elderly?
- Are bodybuilding diets healthy?
- Are cast iron pans unsafe?
- How valid is BMI as a measure of health and obesity?
References
- ^ Mahmoud Barbarawi, et al. Vitamin D Supplementation and Cardiovascular Disease Risks in More Than 83 000 Individuals in 21 Randomized Clinical Trials: A Meta-analysis. JAMA Cardiol. (2019)