Shedding Sunlight on the Coronavirus Epidemic

What exactly is vitamin D and how does it prevent or reduce COVID-19 infection?

Posted Jun 09, 2020

Have you ever wondered why influenza or “flu” season rages on in autumn and winter, then tapers off with the approach of summer? Does the heightened solar radiation in summer kill the virus before it can spread? Or could it be that in summer people spend more time outdoors where the virus particles are less transmissible? Our common sense musings about the seasonality of the flu have also intrigued medical researchers.

In 1981, an English doctor, R. E. Hope-Simpson, devoted himself to studying influenza pandemics. He noticed that cases of influenza decreased in summer and increased in autumn and winter. In his paper “The role of season in the epidemiology of influenza” he proposed that there was a 'seasonal stimulus' for outbreaks of influenza. Hope-Simpson hypothesized that solar radiation might play a role in reactivating the virus from latent carriers. But his research did not go on to prove this hypothesis. Ultimately Hope-Simpson concluded, “The primary agency mediating seasonal control remains unidentified.”

Today, the world is in the grip of a deadly COVID-19 pandemic, with public health experts like Dr. Anthoy Fauci predicting a resurgence of cases and more fatalities in the fall and winter. Public health strategies that can reduce the risk of COVID-19 infection and death are desperately needed. 

A promising trend of research relates back to what Hope-Simpson called the “seasonal stimulus.” New research is looking at the effects of increased sunshine in preventing COVID-19—not because of the effects of radiation on the virus but because increased sunshine produces more vitamin D in our bodies. (I referred to this trend of research on vitamin D in a previous Psychology Today article.)

So what exactly is vitamin D and how does it prevent or reduce COVID-19 infection? Vitamin D is actually not a vitamin at all; it is a hormone. Ultraviolet rays from the sun—specifically Type B ultraviolet rays—produce vitamin D in the skin. It then undergoes a series of biochemical changes in the body and ultimately stimulates the expression of potent anti-microbial peptides. Vitamin D thus plays an important role in the functioning of the immune system.

A new research study, “Association of Vitamin D Deficiency and Treatment with COVID-19 Incidence,” by the University of Chicago School of Medicine was posted in a preliminary version on May 13, 2020. The study concluded that “Vitamin D deficiency that is not sufficiently treated is associated with COVID-19 risk.” This result supports the idea that having an insufficient vitamin D level increases the risk for COVID-19 and suggests that treatment for vitamin D deficiency can reduce that risk.

How much vitamin D do the researchers recommend to parry the risk of Covid-19? Here’s what they say: “Taking 4000- 5000IU of vitamin D daily may be a reasonable approach for persons without known contraindications to vitamin D supplementation.”

The data in the study “argues strongly for a role of vitamin D deficiency in COVID-19 risk and for expanded population-level vitamin D treatment and testing and assessment of the effects of those interventions. Studies of whether interventions to reduce vitamin D deficiency could reduce COVID-19 incidence should be an important priority, including both broad population interventions and intervention among groups at increased risk of vitamin D deficiency and/or COVID-19." 

A mounting body of research suggests that keeping up the body's vitamin D level—either by getting plenty of sunlight or by taking vitamin D supplements—is a good way to strengthen the immune system. A strong immune system helps in fighting off COVID-19 and other viral respiratory illnesses.

Of course, it’s best to consult a doctor about the correct vitamin D dosage. Some doctors will also recommend taking supplements like magnesium and zinc to balance the immune system. A combination of getting plenty of sunshine in summer and taking vitamin D supplements in the autumn and winter months may be a good strategy to keep safe during the pandemic.