Some Northern hemisphere studies have suggested there may be a link between people’s vitamin D levels and COVID-19 outcomes, but, Spotlight reports, leading local experts say there is little evidence to support this.
“For people to be sufficient (in vitamin D) is extremely important, but it’s a completely different issue than (potentially) using vitamin D as a short-term treatment (for COVID-19),” says Professor Marjanne Senekal, professor in nutrition science in the department of human biology at the University of Cape Town. “Whether we want to correct deficiencies or whether deficiencies have played some other role in this situation, (for) the evidence at this stage people are using what they have which is looking at the vitamin D status of patients retrospectively,” she says.
According to Senekal, there is no evidence to make a recommendation that any amount of vitamin D could treat or prevent COVID-19.
A recent article published in the Lancet medical journal states that there is a growing body of “circumstantial evidence” to link outcomes of COVID-19 infection and vitamin D status. Much of this is however contradicted by a large UK Biobank study published in May in which the authors concluded that their findings “do not support a potential link between vitamin D concentrations and risk of COVID-19 infection, nor that vitamin D concentration may explain ethnic differences in COVID-19 infection”.
“Most of this data comes from the Northern hemisphere,” Professor Robin Wood, director of the Desmond Tutu HIV Centre is quoted in Spotlight as saying, and while the concept of pigmented skin in temperate zones might increase vitamin D deficiency, it cannot be interpreted as a full explanation for COVID-19 outcomes.
Sharing more insights into some epidemiological data, Wood says that Finland has the lowest incidence levels of the Scandinavian countries and it’s also the most aggressive on food fortification. “Another one is Belgium (which has) the highest incidence rates in Europe. When I looked up their vitamin D status, there was a paper from a few years ago that showed 44% of Belgium (persons) in the study were deficient,” he says. But Wood calls this “cherry picking”, meaning that data could be chosen to fit a hypothesis that vitamin D could be linked to COVID-19 outcomes.
Wood emphasises that while there is a large amount of circumstantial evidence as suggested by the Lancet article, it’s not strong enough to suggest any causation.
Senekal stresses that vitamin D is no “magic bullet” in the prevention or treatment of disease. Although vitamin D sufficiency is important, she says it is only one factor in what she calls a “complex soup” of genetic and dietary factors, and physical activity, nutritional status, age and overall health that determine a person’s susceptibility to disease.
Spotlight says both Senekal and Wood caution against taking too much vitamin D through supplementation, as this can be harmful to the body and has no proven preventative effect against disease.
In 2017 a review study published in the BMJ suggested that vitamin D supplementation protected against acute respiratory infections. The study comprised of data from over 11 300 participants from 25 randomised trials. It found that supplementation was particularly effective in reducing the risk of infection for persons with lower baseline levels – in other words, people who were deficient. What the study defines as an acute respiratory infection is not clear-cut. Researchers write that definitions were “diverse, and virological, microbiological or radiological confirmation was obtained for the minority of events”.
While the findings may make vitamin D seem like a potential prevention method for COVID-19, Wood cautions on the study’s grouping together of all respiratory diseases. “It doesn’t surprise me that they could show a benefit if they put all the endpoints, all respiratory disease together, but it doesn’t change the real understanding of the role of vitamin D,” he says. “There are other studies which don’t show benefit, so it shouldn’t be jumped onto to say that therefore COVID-19 is going to be cured by giving vitamin D to everybody.”
Senekal says the study confirms the underlying issue with deficiency and reiterates the importance of sufficiency at all times.
Full Spotlight report
The Lancet article
Nutrition Today article
BMJ review study