As the saying goes, “Another day, another dollar.” That’s how people shilling for shady Covid-19 cures must view the pandemic. One day it’s ivermectin, the next it’s hydroxychloroquine or colloidal silver.

No stranger to the Covid-19 sweepstakes is vitamin salesman Joseph Mercola, “The Most Influential Spreader of Coronavirus Misinformation Online,” as the New York Times headline put it in 2021.

“There is simply no question that vitamin D optimization is a crucial component of COVID-19 prevention and treatment,” wrote Mercola in his subscription newsletter in September.

Covid claims have landed Mercola in hot water before. In 2021, the FDA warned him not to suggest that his vitamin D supplements could prevent or treat the virus, and YouTube banned him, in part for spreading misinformation about Covid vaccines.

Screenshot from Dr. Mercola website
Vitamin D prevents and treats Covid-19, says Joseph Mercola. In the best studies, that’s just not true.

Mercola was so sure that vitamin D both prevents and treats Covid-19 that, in September, he wrote that “we do not actually need randomized controlled trials.” Really?

Most of the evidence that Mercola cites comes from observational studies, which follow people and record their health outcomes. Those studies are useful, especially in exploring new hypotheses. But sorting out what causes what can be a real headache.

For example, could vitamin D takers have milder Covid-19 infections because they’re more likely to get vaccinated, have fewer health problems, or have better access to medical care? Researchers try to take those and other “confounders” into account, but they can’t adjust for unknown confounders.

In contrast, randomized controlled trials randomly assign people to either a treatment like vitamin D or a control group. If the treatment outperforms the control, it’s likely that the treatment works.

As it happens, Mercola’s vitamin D article appeared the day before the results of two huge trials were released.

Researchers in the UK and Norway had randomly assigned 40,000 volunteers to take vitamin D or not for six months. Different countries, same result: vitamin D had no impact on Covid-19 risk.

And in three other trials, vitamin D showed no clear benefit in treating Covid-19.

Two more studies are on the way. For now, as the National Institutes of Health says, there is “insufficient evidence” for taking vitamin D to prevent or treat Covid-19.

Of course, it’s important to get enough vitamin D, especially for strong bones. But it would be folly to rely on the vitamin when we already have effective vaccines and treatments.

Please don’t let a misinformation superspreader convince you otherwise.

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