- During the COVID-19 pandemic, medical scientists have been closely examining the effects of vitamin D deficiency.
- Meta-analyses of data from 45 studies have shown a significant correlation between vitamin D deficiency and more severe symptoms, complications and death from COVID-19.
- Although laboratory studies on the relationship between vitamin D deficiency and COVID-19 are still in progress, previous studies have shown vitamin D supplementation to be protective against other acute respiratory tract infections in people who are vitamin D deficient.
Medical scientists investigating the association between vitamin deficiency and illness in humans have long known that adequate levels of vitamin D must be maintained for health. During the early days of the COVID-19 pandemic, there were observations that people with vitamin D deficiency may be at greater risk for suffering complications and death.1 Recently, the scientific community has begun to take a closer look.2
Within the last month, three health organizations in the United Kingdom published reports advising people to make sure they maintain adequate levels of vitamin D, either through controlled sun exposure or vitamin D supplements. While cautioning that more research is needed, the Scientific Advisory Commission on Nutrition, the National Institute for Health and Care Excellence and the Royal Society discussed the health benefits of vitamin D.3
Study Found Correlation Between Vitamin D Deficiency and COVID-19 Mortality
Recently, researchers in Dallas, Texas analyzed data sets from ten European countries and found a strong correlation between severe vitamin D deficiency and death rate per million from COVID-19. Looking at data from the U.K., Ireland, France, Germany, Belgium, the Netherlands, Denmark, Finland, Norway and Estonia, the researchers concluded that the “correlation coefficient of 0.76 indicates that approximately 58% of COVID-19 mortality can be explained by severe deficiency in vitamin D.4
This study has not yet been peer reviewed, but the authors report the correlation was strong enough for them to recommend “universal screening for Vitamin D deficiency, and further investigation of vitamin D supplementation in randomized control studies, which may lead to possible treatment or prevention of COVID-19.”5
According to Adrian Martineau, PhD, professor of respiratory infection and immunity at Barts and The London School of Medicine and Dentistry, Queen Mary University of London, although there have been no laboratory studies specifically evaluating the effects of vitamin D on the immune response to the SARS-CoV-2 virus, studies have looked at the role of vitamin D levels in other respiratory viral infections. According to Dr. Martineau, those studies have shown that vitamin D metabolites “augment innate antiviral immune responses while simultaneously dampening down inflammation, which has been highlighted as a major problem in covid-19.”6 He added:
This combination of actions makes vitamin D an interesting candidate both as a potential tool in covid-19 prevention and as an adjunct to other therapies for people who already have the disease.
While some observational studies suggest that there may be an association between low vitamin D levels and higher rates of COVID-19 infection, others have found no correlation between vitamin D supplementation and risk for or severity of COVID-19.7
Evidence for Link Between Vitamin D Deficiency and Respiratory Infections
The link between vitamin D deficiency and severity of symptoms during respiratory infections has been well documented. As more public health agencies begin to look at the potential benefits of vitamin D supplementation to treat or alleviate symptoms of COVID-19, previously published evidence for a link between vitamin D levels and other respiratory illnesses is being re-examined.
In 2017, a systematic review and meta-analysis of data on 10,933 patients from 25 randomized, controlled trials concluded that vitamin D supplementation was strongly protective against acute respiratory tract infection among all participants.8 This meta-analysis has garnered a lot of attention recently. According to the British Medical Journal, the article has been accessed on line more than 300,000 times since the beginning of the pandemic.9
This same analysis by Martineau et al., as well as three others that also reported a protective effect of vitamin D supplementation, were reviewed for the World Health Organization (WHO).10 In their commentary, the authors noted that in the 45 studies included in the various analyses, a consistent benefit was shown for vitamin D supplementation for preventing respiratory tract infection. Three showed a particular benefit in children younger than 16 years of age; two of the three reported that the protective effect was only seen with single daily doses but not with a bolus, or loading dose.
One of the reviews suggested that doses of 800 IU or less were protective, but higher doses were not. Noting that vitamin D deficiencies are common worldwide, reviewers concluded that further studies are needed to evaluate different doses and intervals of supplementation, as well as to determine whether there is any additional benefit to be had once vitamin D levels have been normalized.
Health Benefits of Vitamin D
An essential nutrient, vitamin D plays an important role in keeping a number of the body’s systems healthy. Besides promoting healthy bones and teeth, vitamin D also supports immune, brain and nervous system health, regulates insulin levels, supports lung and cardiovascular function.
Vitamin D is more accurately described as a prohormone, a precursor to a hormone, rather than a true vitamin solely obtained from food. Vitamin D is primarily generated in the human body through exposure to sunlight, though it also can be acquired through certain foods such as oily fish, red meat, egg yolks and fortified milk and juices.11
Explaining vitamin D’s critical effects on the immune system, Habib Sadeghi, DO states:
As an immunomodulator, it’s central to regulating the body’s immune response by interacting with immune cells that produce vitamin D-activating enzymes. In this way, vitamin D ensures the immune system remains in balance and reacts appropriately to various threats.12
Dr. Sadeghi adds that vitamin D also is known to have potent antimicrobial properties and was historically used successfully to treat infectious diseases, including tuberculosis and leprosy, before the introduction of antibiotics.
Causes of Vitamin D Deficiency
Several factors can contribute to decreased vitamin D levels. Both the increased levels of melanin in darker skin and the use of sunscreen, for example, can hamper the absorption of ultraviolet radiation B (UVB) rays from the sun necessary for the skin to produce vitamin D. Similarly, those who live at northern latitudes, those who work night shifts or are otherwise unable to get adequate sun exposure, and some babies who are exclusively breastfed may also develop vitamin D deficiency.13
However, too much vitamin D can cause toxicity, usually resulting from overuse of supplements, which can lead to dehydration, increased thirst, vomiting, abdominal cramps and mental confusion.14
Vitamin D deficiency is more common among people who smoke, as well as among those who are obese or have diabetes and high blood pressure—all chronic health conditions that have been associated with increased risks for COVID-19 complications and death. Some have speculated that during the winter months of 2020, with many people sheltering indoors, the chances of developing vitamin D deficiency were increased.15
There are currently 28 registered human clinical trials underway to evaluate the potential relationship between vitamin D and COVID-19. Results of those studies are expected to clarify whether supplemental vitamin D might have a positive role to play in the management of COVID-19 patients with low vitamin D levels.16
1 Kubala J. Can Vitamin D Lower Your Risk of Covid-19? HealthLine Mar. 26, 2020.
2 Landsverk G. Vitamin D May Be A Good Defense Against The Coronavirus, According To Several New Reports. Here’s What You Need To Know. Insider July 7, 2020.
4 Robertson S. More Evidence On Vitamin D Deficiency And Death Rates From COVID-19. News-Medical.Net July 2, 2020.
5 Pugach IZ, Pugach S. Strong Correlation Between Prevalence Of Severe Vitamin D Deficiency And Population Mortality Rate From COVID-19 In Europe. medRxiv June 24, 2020.
6 Torgesen I. Covid-19: Public Health Agencies Review Whether Vitamin D Supplements Could Reduce Risk. BMJ June 19, 2020.
7 McCall B. Medical Societies Advise on Vitamin D in Midst of COVID-19. Medscape July 10, 2020.
8 Martineau AR et al. Vitamin D Supplementation To Prevent Acute Respiratory Tract Infections: Systematic Review And Meta-Analysis Of Individual Participant Data. BMJ Feb. 15, 2017.
9 See Footnote 6.
10 Aponte R, Palacios C. Vitamin D For Prevention Of Respiratory Tract Infections. World Health Organization June, 2017.
11 Ware M. What Are The Health Benefits Of Vitamin D? Medical News Today Nov. 7, 2019.
12 Astorino DM. Can Vitamin D Help Keep You Safe From COVID-19? A Doctor Breaks It Down. Microsoft News June 2, 2020.
13 See Footnote 11.
14 Gaze DC. Does Vitamin D Ward Off Coronavirus? Don’t Reach For The Supplements Yet. The Conversation June 25, 2020.