Editor’s Note: Every Wednesday, James Hamblin takes questions from readers about health-related curiosities, concerns, and obsessions. Have one? Email him at email@example.com.
Dear Dr. Hamblin,
I have read that a higher vitamin-D level correlates with better outcomes for other coronaviruses such as SARS and MERS. Could skin color be one of the reasons black Americans and Hispanic Americans are disproportionately affected by COVID-19? Should we be taking vitamin-D supplements? After consulting with my GP, I started taking 1,000 IU of vitamin D, since I’m only leaving the apartment once every two to three weeks. I’m Chinese, and I’ve experienced some aggression since the pandemic began. I’m more afraid of getting stabbed than getting sick. Being indoors all the time, I’m probably not getting enough vitamin D anyway.
Brampton, Ontario, Canada
I think taking that small dose is reasonable to do, given the circumstances.
I don’t often say that. The internet is full of enticing advertisements for dietary supplements that imply they will protect us from the coronavirus. Wellness influencers have recommended elderberry, and QAnon leaders have advised followers to purchase a product called Miracle Mineral Solution. Tom Brady launched a vitamin tonic that, he claims, will protect you from “whatever comes your way.” Even if a product is unlikely to directly hurt you, any false sense of safety can absorb money and attention that could’ve gone to efforts to help people through the pandemic.
But in this opportunistic milieu, vitamin D stands out as a dietary supplement that’s steadily gained actual scientific traction. Most people are unlikely to be helped by it, but many potentially could be.
Taking vitamin D to mitigate the threat of COVID-19 was one of the earliest suggestions to come from virus researchers in China. A lifetime ago, in early February of 2020, Lei Zhang and Yunhui Liu at China Medical University were urgently searching for out-of-the box approaches to fight the novel coronavirus—which, they warned, “may spread worldwide [as a] pandemic.” Based on what was known about other coronaviruses, Zhang and Liu broke down the existing research on all kinds of nutrients and minerals, including iron and omega-3 fatty acids, zinc and flavonoids, to see whether anything might be worth trying.
They found small bits of evidence suggesting possible pathways for some nutrients. Vitamin A, for example, is a retinoid—a class of compounds that has been found to inhibit replication of the measles virus. It can also enhance people’s immune responses, potentially making healthy cells slightly more resistant to viral invasion. Vitamin E appears to have some rudimentary protective effects against similar viruses. Mice with vitamin-E deficiencies are more likely to have heart injury as a result of the coxsackievirus, an RNA virus like the coronavirus.
Perhaps the researchers’ most promising suggestion, though, was vitamin D. D isn’t like other compounds we refer to as “vitamins” (a nomenclature convention we’d be better off without), because it’s not really a nutrient, but a hormone. It doesn’t naturally occur in our food system; instead, foods such as milk and cereal are “fortified” with a synthetic version of vitamin D. And unlike any other “vitamin,” we can make D ourselves. Our own skin manufactures the compound when exposed to sunlight.
Before we built skyscrapers and started spending almost all of our time indoors, people had less of a problem getting enough vitamin D. Now, even though very little sunlight is required to avoid a deficiency, it is common among people who are house-bound or institutionalized in hospitals, nursing homes, or prisons. In their research, Zhang and Liu noted that the coronavirus mostly affected these same populations. So, the researchers posited, “Vitamin D could work as another therapeutic option for the treatment of this novel virus.”
There is a tangle of variables in “could.” Crowded indoor spaces are the most likely environments for viral transmission, and the people in nursing homes are older and more likely than the general population to have chronic conditions (besides or in addition to vitamin-D deficiency) that could make them vulnerable to severe cases of COVID-19. People in prisons generally have limited access to health care.
Even so, other interesting connections have begun to bear out the vitamin-D hypothesis. In April, a small study from the Philippines showed a correlation between vitamin-D levels and better outcomes for patients with the disease. In May, a study led by Vadim Backman, a professor at Northwestern University, found a similar correlation between severe vitamin-D deficiency and death rates among people with COVID-19. His research team found that, in general, people in countries with high COVID-19 mortality rates had lower levels of vitamin D compared with patients in countries that were not as severely affected.
There are also plausible mechanisms to suggest that these correlations might not be entirely due to chance. Vitamin D is most famous for its role in bone health, but it has an important role in the immune system, specifically in the maturation of some white blood cells. Having low levels of vitamin D has long been known to leave people susceptible to various infectious diseases, including upper respiratory tract infections.
In addition to fortifying the immune system, vitamin D might assist in preventing it from becoming overactive. Backman and his team reported that people with adequate vitamin-D levels were less likely to experience a cytokine storm, a misdirected inflammatory response that ultimately kills many people with COVID-19. The researchers posit that vitamin D may decrease this risk by helping to appropriately calibrate the inflammatory response.
Although all of these correlations and mechanisms have not yet borne out in clinical trials (which are underway), some researchers say that in the meantime, the default should be for everyone to take small amounts of vitamin D. Health officials in the United Kingdom have already begun recommending that people do so for the remainder of the pandemic. Rose Kenny, a gerontologist at University of Dublin, told me she believes that all public-health entities should be recommending the same. “I feel very passionately about this,” she said. Given the low risk of harm, even a small benefit would be worthwhile, she said. “It’s a bit of a no-brainer.”
This sounds reasonable, especially considering that everyone is advised to stay at home as much as possible, meaning less exposure to sunlight. But such advice should come with caveats. For one, as with any pre-hormone someone ingests, taking excessive vitamin D can be dangerous. And most people will probably see no benefit from taking vitamin D, unless they’re deficient to begin with. Any benefit would most likely be in mitigating the severity of disease—not preventing it. That means taking vitamin D is no excuse to ease up on social distancing and masks (sorry).
Looking to a supplement to combat COVID-19 also risks distracting from the heart of the problem. It’s true that darker-skinned people are more likely to have a vitamin-D deficiency, in part because melanin in the skin mitigates the absorption of sunlight needed to convert the hormone to its active form. But racial disparities in COVID-19 infections have been far more dramatic than this effect could even potentially account for. Black Americans constitute 13 percent of the United States population, but 24 percent of deaths (where race is known). In England, black people are more than four times more likely to die of COVID-19 than white people are. The differences in disease burden we see around the world will not be explained by any single compound, nor will they be addressed by one.
There are more obvious determinants of who suffers from severe disease. There are racial disparities in testing and access to medical care, as well as class systems that perpetuate chronic health conditions. Immune health is a function of age, chronic disease, nutrition, stress levels, wealth, and status. The precision of one’s immune system is a proxy for all of these things. If vitamin D is a factor in this mix, it would be as one of a thousand pinpricks. Individual dietary compounds might tweak the algorithm of how this disease plays out, but the algorithm itself needs to be rewritten.
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