Scientists agree on the basic hygiene principles to avoid infection as well as on the primary way the virus is transmitted. As for a slew of other preventative or causational factors — the jury’s out.
That includes Vitamin D.
“Recent studies on Vitamin D, they raise an eyebrow. They might be hypothesis-generating, and it’s a good question to ask, but it’s premature to start making claims about vitamin D and COVID-19,” said Isaac Bogoch, an infectious disease specialist based out of Toronto General Hospital.
“We call this ‘speaking beyond the data.’ And that’s what happening with vitamin D.”
Vitamin D is well known for its role in keeping healthy bones, teeth and muscles by promoting the body’s absorption of calcium. A lack of it has its downsides and risks, including bone weakness (osteoporosis) in adults and a similar bone deformity illness, called rickets, in children.
There have long been suggestions that vitamin D boosts the immune system and helps stave off infections, including the common cold. Since the inception of COVID-19, studies have pointed to the vitamin’s possible role in the prevention of infection and how supplementation could improve a person’s outcome.
In theory, there may be some weight to the claims, said Bogoch, but overall the evidence is inconsistent.
“It’s being studied, and rightfully so, but these claims of efficacy are overstating the data based on what we have today,” he said.
“If there were easy answers, we’d find them already.”
What do studies say?
One study at the University of Chicago Medicine reviewed health records of more than 4,300 patients who tested positive for COVID-19 in March and April, of whom 499 had been tested for vitamin D levels in the previous year.
The researchers found that people with vitamin D deficiency at last testing and did not increase doses were 77 per cent more likely to be infected with the virus than those with sufficient levels.
The study has not yet been peer-reviewed, but its lead author, Dr. David Meltzer, suggested to the New York Times that it’s likely people taking vitamin D who contract the virus will have fewer symptoms “because the immune system will be less likely to have an exaggerated inflammatory response.”
Other studies have found that vitamin D deficiency is “prevalent” in severe cases, or that low levels are linked to mortality, or even that higher rates of infection in minority groups in the U.K. and U.S. suggest a role for vitamin D, as they tend to have lower levels of vitamin D.
But it’s hard to parse out vitamin D from all the other risks and factors associated with COVID-19, said Kelly Grindrod, a pharmacist, and professor at the University of Waterloo’s School of Pharmacy.
How susceptible someone is to the virus can be impacted by pre-existing health conditions, like cardiovascular disease, hypertension, diabetes, other respiratory diseases, cancer and kidney disease.
Low levels of vitamin D are also associated with many of these conditions, said Grindrod.
“We might think, if we just got their vitamin D levels up, we wouldn’t be in this position,” she said. “But it may actually be reverse causation, which is that people who have all those conditions have lower vitamin D. That seems to be the thing with COVID as well.”
It’s why randomized control trials, which aim to reduce certain sources of bias when testing the effectiveness of new treatments, are needed, she said.
The research so far stems from “large observational studies,” which have their place, said Grindrod, but can only provide signals and clues.
Almost all of the studies acknowledge that further research is needed.
“There are many other conditions being studied, but so far, vitamin D supplementation hasn’t been panning out,” she said. “Having low vitamin D may be a risk — whether it’s vitamin D alone or something that leads to low vitamin D — but simply supplementing it doesn’t fix the problem.”
Other studies are also of that thinking.
A review of evidence by Britain’s National Insitute for Health and Care Excellence (NICE) suggests there is nothing to support taking vitamin D supplements to prevent or treat COVID-19. The U.K. already recommends increased vitamin D intake during the winter months when sun and time outdoors are limited and bodies are bundled from the cold.
Another analysis from the U.K. Biobank did not support a link between vitamin D concentrations and risk of virus infection, nor that vitamin D levels could explain ethnic differences in getting infected.
“What we have today are studies of dubious quality that either endorse or refute,” said Bogoch. “What we have not seen is high-quality data on this front.”
What you can do
People should be getting appropriate amounts of vitamin D regardless of COVID-19 risk, the experts agree.
Guidance from the Institute of Medicine — backed by Health Canada — says most adults get 600 international units (equivalent to 15 micrograms) of vitamin D from food or supplements daily. If they are aged 71 and older, it’s more like 800.
Health Canada continues to recommend people over the age of 50 take a daily vitamin D supplement of 400 international units as aging leads to reduced dietary intake and the ability to synthesize vitamin D from the sun.
Bogoch cautioned that any changes in supplementation — vitamin D or otherwise — should always be done in consultation with a doctor.
The advice on adequate vitamin D intake “was already there,” Grindrod added.
“Whether it’s going to help you with COVID? Well, there’s a whole lot more that could help protect you from COVID, like, say, washing your hands.”
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