Does vitamin D ward off coronavirus? Don’t reach for the supplements yet

It has been suggested that taking vitamin D may protect people from getting COVID-19. But should we be using supplements to ward off the virus? We need to separate fact from fiction.

Vitamin D is essential for maintaining overall health, especially for bones, teeth and muscle. It regulates the body’s stores of calcium and phosphate and helps us maintain a healthy immune system. While we can get vitamin D from oily fish, egg yolks, red meat and supplemented foods in our diet, the vast majority of vitamin D in the body is produced in the skin due to sunlight exposure.

Vitamin D concentrations are lower in people with obesity, those with high blood pressure or diabetes and in those who smoke. It can be stored in fat cells, thus reducing the circulating concentration in the blood. Poor diet in those with heart disease and a sedentary lifestyle away from sunlight contribute to lower blood concentrations of the vitamin, while smoking affects vitamin D and calcium regulation.

These conditions are associated with increased risk of COVID-19 and the more severe forms of the disease. It has therefore been proposed that people with low vitamin D are at higher risk of infection or have worse outcomes with COVID-19.

Northern hemisphere

Between October and April, most of Western Europe and the northern states of North America lie too far north to have enough sunlight to provide adequate production of vitamin D in the skin. Many people in these places are at risk of becoming deficient during these six-months unless they get increased levels of the vitamin from their diet or supplements.

At the start of the pandemic, the northern hemisphere was emerging from the winter months of 2019-20. Also, with the lockdown, many people were isolating or shielding inside with very little exposure to natural sunlight. This will have had a negative effect on vitamin D concentration, making some people deficient and thus compromising immune system function.

Italy, Spain, the UK, China and some parts of North America all have a high proportion of the population with vitamin D deficiency. These countries also have significantly higher numbers of COVID-19 deaths. Other countries in the same region such as Norway, Denmark and Finland have lower COVID-19 mortality rates, but higher levels of vitamin D in the population as supplementation and fortification of food in these countries is common.

It has also been highlighted that people from Black, Asian and minority ethnic (BAME) backgrounds make up a large proportion of patients with severe COVID-19 requiring intensive care in the UK. Low concentration of vitamin D in BAME people in the northern hemisphere may contribute to a greater risk, however, infants and children of all ethnic backgrounds who are often vitamin D deficient don’t have a greater risk of COVID-19.

Further data analysis, specifically looking at ethnicity and vitamin D in COVID-19, would be needed to draw firm conclusions, and the discrimination faced by these populations cannot be overlooked.

Treating COVID-19?

Researchers have combined literature searches with statistical cross-sectional studies to assess the effect of vitamin D level on COVID-19.

Some suggest there is no evidence to support vitamin D dosing in preventing COVID-19 while others have produced evidence for supporting the use of supplements. What is apparent is that we need more dedicated studies to assess any relationship between vitamin D and COVID-19.

Currently, 28 trials have been registered relating to vitamin D and COVID-19. The reporting of these findings will better guide the management of patients presenting with low concentrations of vitamin D.

Although vitamin D is beneficial to health, it should be noted that too much can be toxic and can cause dehydration, increased thirst, vomiting, abdominal cramps and mental confusion.

There have been reports that taking very large doses (so-called “megadoses”) of vitamin D supplements will prevent COVID-19 infection. This is simply not true. There is no scientific evidence to support large doses of vitamin D being protective enough to outweigh the toxic effects.

We do not yet have a full clear picture of the relationship between vitamin D and COVID-19, but if your blood concentrations are found to be low, or you are shielding out of direct sunlight, it’s never a bad idea to see your doctor about taking supplements – just don’t take too many.

Dr David C. Gaze is affiliated with The Association for Clinical Biochemistry and Laboratory Medicine; The American Association of Clinical Chemistry; Royal Society of Medicine; Pathological Society of Great Britain & Ireland; European Society of Pathology.