Wed | Dec 1, 2021

Michael Abrahams | COVID-19 and the relevance of vitamin D

Published:Tuesday | November 23, 2021 | 12:06 AM

Vitamin D has long been recognised for its importance in calcium and bone health and preventing rickets, a condition in children that causes poor bone growth and can lead to deformities. However, since the turn of the century, research has found...

Vitamin D has long been recognised for its importance in calcium and bone health and preventing rickets, a condition in children that causes poor bone growth and can lead to deformities. However, since the turn of the century, research has found that vitamin D is crucial for the efficient functioning of the immune system, as it influences immune cells, has anti-inflammatory and antiviral activity, and exerts a protective effect on blood vessels.

Vitamin D has also been found to regulate gene expression, influencing more than 2,500 genes, and in doing so, is of value in fighting some of our most serious maladies, including cancer, diabetes mellitus, acute respiratory tract infections and autoimmune diseases.

For example, a recent observational study found that women who consume higher levels of vitamin D have a reduced risk of developing early-onset colorectal cancer. The link between vitamin D levels and colorectal cancer risk has been observed for years, and studies are still ongoing. Another recent prospective, population-based study of men found lower vitamin D levels to be associated with increased all-cause mortality. In other words, those with low vitamin D levels did not live as long as those with normal ones.

This month, the Council for Responsible Nutrition’s Vitamin D & Me! Education initiative released a report that highlighted 13 meta-analyses (examinations of data from a number of independent studies of the same subject) including over three million participants. They concluded that “higher blood levels of vitamin D are correlated with lower incidence or severity of COVID-19 in most of the research”. One meta-analysis found that the odds of getting infected with SARS-CoV-2, the virus that causes COVID-19, increased by 3.3 times in individuals with vitamin D deficiency, and the probability of developing severe COVID-19 disease over five times higher in persons who are deficient in vitamin D.


Evidence that vitamin D status affects the risk of COVID-19 comes primarily from observational studies. Observational studies, however, are vulnerable to two statistical issues: ‘confounding’ and ‘reverse causation’, and these must be taken into consideration when interpreting data from these studies on vitamin D and COVID-19. Regarding confounding, this occurs when other variables can influence the outcome. For example, being elderly and having a chronic disease can not only affect a person’s vitamin D level, but also their risk of contracting COVID-19. Reverse causation occurs when the outcome being evaluated affects the variable under investigation. In this case, it is possible that severe COVID-19 might reduce vitamin D levels.

On the other hand, the gold standard in research is a randomised controlled trial. In such a trial, involving vitamin D supplementation, for example, the population receiving the vitamin would be chosen at random from an eligible population, and a control group also chosen at random from the same eligible population. Subsequently, the outcomes from the two groups would be compared. Studies such as these yield more objective results.

However, in the paper ‘Evidence Regarding Vitamin D and Risk of COVID-19 and Its Severity’, published in the journal Nature, its authors claim, “The evidence to date generally satisfies Hill’s criteria for causality in a biological system, namely, strength of association, consistency, temporality, biological gradient, plausibility (e.g., mechanisms), and coherence, although experimental verification is lacking. Thus, the evidence seems strong enough that people and physicians can use or recommend vitamin D supplements to prevent or treat COVID-19 in light of their safety and wide therapeutic window.”


In the absence of large randomised clinical trials, which are very expensive and take a long time to complete, health authorities are unlikely to recommend vitamin D supplementation as public health policy. However, based on the research so far, it may be of value. The body uses sunlight to make vitamin D, and there is a lot of sunlight in Jamaica. On the other hand, most of the populace is of black African descent, and dark-skinned people are more prone to deficiency of the vitamin due to the presence of increased melanin in their skin. The pigment absorbs the ultraviolet radiation from the sun and, hence, decreases the amount of vitamin D manufactured when compared with lighter-skinned individuals. Also, many of us spend little time outdoors in direct sunlight. In addition, only a few foods, such as fatty fish, contain significant amounts of the vitamin.

So, vitamin D supplementation and checking your vitamin D level may be a good idea, certainly one whose potential benefits outweigh its risks. And there are risks, for although vitamin D is important for our bodies, it is possible to take too much and experience effects from its toxicity.

There is also no evidence that good vitamin D levels alone will protect you from COVID-19. Vaccination, public health measures, and having a healthy lifestyle, including exercising, consuming a healthy diet, losing excess weight, and stress management, are also of vital importance. We need all the help we can get to fight this wretched plague.

Michael Abrahams is an obstetrician and gynaecologist, social commentator and human-rights advocate. Send feedback to and, or follow him on Twitter @mikeyabrahams.