Amid the constant focus on seeking relief from the deadly pandemic, the role of Vitamin D has been gaining momentum in the absence of a Covid-19 cure.
According to BBC and the Guardian, the government of England has announced that more than 2.5 million vulnerable people will be offered free vitamin D supplements this winter.
Although it would be too farfetched to say as of yet that higher level of vitamin D will protect from Covid-19, some recent studies have suggested a link between low vitamin D levels and a higher risk of catching the disease.
Adrian Martineau, who studies respiratory infections and immunity at Queen Mary University of London, told Live Science, "These studies don't prove that vitamin D deficiency causes increased Covid-19 risk, rather it's suggestive and it's enough to justify doing further research to find out whether or not there is a true cause-effect relationship."
The database ClinicalTrials.gov lists about 30 such studies of vitamin D and Covid, according to The Scientist.
A study published on 3 September in JAMA Network Open, the researchers examined the relationship between likely vitamin D levels and Covid-19 risk in 489 people who took a Covid-19 test at the University of Chicago Medicine between March 3 and April 10 and whose vitamin D levels had been measured within the previous year. They found that the risk of Covid-19 infection in people with vitamin D deficiency was nearly two times higher than in people with sufficient levels of the vitamin. Another study, published on 27 October in The Journal of Clinical Endocrinology & Metabolism, found that hospitalized Covid-19 patients had higher rates of vitamin D deficiency than a control group of patients who didn't have Covid-19 but whose vitamin D status was measured pre-pandemic.
Dr David Meltzer, researcher who led the study at University of Chicago, agreed that none of it proves that vitamin D deficiency is causing Covid-19.
Meltzer said, referring to his study and to other associations between vitamin D and Covid risk, "It may be that people who are sicker in general are more likely to have low vitamin D levels."
Vitamin D, often referred to as the sunshine vitamin, can be obtained from sunlight exposure during the period of late March to the end of September. The body creates vitamin D from direct sunlight on the skin when outdoors, but in winter (between October and early March) people do not get enough vitamin D from sunlight.
Because of the Covid-19 pandemic and lockdown measures most people are keeping inside than usual, leading to a higher risk of a vitamin D deficiency.
How Can Vitamin D Be Protective?
A review of research by the UK National Institute of Health and Care Excellence (NICE) suggests there is no evidence to support taking vitamin D supplements to specifically prevent or treat coronavirus but it may have some broader health benefits during the pandemic to keep people as nutritionally fit as possible.
Some researchers have suggested that vitamin D deficiency might be linked with poorer outcomes if someone catches coronavirus. But other underlying risk factors, such as heart disease, are common in these patients too, making it hard to draw conclusions.
Moreover Vitamin D has been shown to boost the immune system's response to viruses and dampen its inflammatory response.
According to a meta-analysis by Martineau, vitamin D supplementation reduced the risk of acute respiratory tract infections in general compared with a placebo. However, the meta-analysis did not include studies about Covid-19.
An earlier study published on 6 May in the journal Aging Clinical and Experimental Research found that, the lower the average vitamin D levels, the higher the rate of coronavirus cases and deaths were.
Additionally, there's an overlap between the groups of people with higher risk of vitamin D deficiency. Such as older people and people with darker skin, and those at higher risk for Covid-19. "People put two and two together and thought, 'Well, this is quite a striking coincidence, if it is indeed a coincidence," Martineau said.
Nevertheless, not all studies have suggested a protective effect. A study published on 7 May in the journal Diabetes & Metabolic Syndrome found no statistically significant association between vitamin D levels and Covid-19 risk once the researchers took into account other factors that could affect Covid-19 risk.
Should we start taking vitamin D?
Public Health England recommends vitamin D throughout the year for those who are not often outdoors, live in a care home, people with dark skin or people who usually wear clothes that cover up most of your skin when outside.
Britons were advised to take 10 micrograms of vitamin D a day between October and early March by the Public Health England (PHE).
In the US, the daily recommended vitamin D intake is 600 international units (IUs) for adults up to age 70 and 800 IUs for adults 71 and up, according to the National Institutes of Health Office of Dietary of Dietary Supplements.
According to Adrian Martineau, people can consider taking supplements only if they aren't already meeting current guidelines for vitamin D intake from food. He, however, does not recommend people to start taking higher doses of the vitamin in the absence of more data about how dosage and Covid-19 risk are related.