An Immune System Supercharger

Vitamin D appears to help prevent many illnesses, including COVID

By Adam Meyer Published Nov 14, 2022 17:06:34 IST
An Immune System Supercharger illustrations by James Steinberg

Since the early 20th century when vitamin supplements first became available, people have generally focused on a single, specific benefit attributed to each vitamin. ­Vitamin A, for instance, could optimize your eyesight. B vitamins could give you extra energy. Vitamin E could make your skin glow. Thanks to Linus Pauling, vitamin C supplements were popular in the 1970s and 1980s for helping to ward off colds (a theory since debunked by numerous studies). Despite the fact that each vitamin actually delivers a range of benefits, it’s often one characteristic that gets all the attention. And thanks to the ­­COVID-19 pandemic, the public’s recent focus has been on vitamin D and its immune system benefits.

A 2020 study published in the Journal of Clinical Endocrinology & Metabolism (JCEM) found that more than 80 per cent of people hospitalized for ­COVID-19 had low vitamin D levels. And according to a 2020 report published in, an estimated 490 million Indians are vitamin D deficient, which—based on information from the JCEM study—could make them more susceptible to the virus. Before vaccines against the novel coronavirus became available, people started downing vitamin D supplements, hoping to prevent ­COVID illness.

More research appears to confirm the connection. A January 2022 peer-reviewed meta-analysis published in the journal Reviews in Endocrine and Metabolic Disorders noted that several studies have suggested a significant association between vitamin D deficiency and an individual’s ­COVID-19 susceptibility and severity. Research done before the pandemic had found that vitamin D plays a role in minimizing the risk of respiratory infections and is associated with reduced potential for blood clots, which the researchers of the 2022 review stated “are a common and major cause of death among patients with ­COVID-19.”

What scientists still don’t know for sure is whether the increased likelihood of getting severe ­COVID-19 is directly caused by low vitamin D blood levels—or whether having low vitamin D levels just leads to poorer health overall. And the big question: Can taking vitamin D supplements help people avoid getting ­COVID-19?

William Schaffner, MD, professor of preventive medicine and infectious diseases at the Vanderbilt University School of Medicine, says, “Vitamin D deficiency is associated with ­COVID-19 severity, but research doesn’t show it’s the cause specifically.” He adds: “Your best bet is to assume that vitamin D helps prevent ­COVID-19 and reduces the severity of symptoms, or at least is a healthy and safe option for strengthening your immune system to fight off disease.”

Fatty fish (salmon, tuna, mackerel) and fortified dairy products are the main dietary sources of the vitamin. The body also synthesizes vitamin D from sunlight, but indoor life and strong sunblock reduce that source of the vitamin too. People who have chronic illnesses, elderly people, and people with darker skin are at particular risk of being deficient.

All these are examples of why many medical experts recommend vita-min D supplements. Supplementing with vitamin D can have many other benefits, including helping the body absorb calcium from the digestive tract in order to build healthy bones. Other, lesser-known health effects include:

  • Vitamin D may be associated with a lower incidence of several urologic problems in adults, such as urinary tract infections and overactive bladder, as well as prostate and bladder cancers.
  • Low levels of vitamin D have been linked with neurodegenerative diseases, such as Alzheimer’s disease and multiple sclerosis.
  • Low levels of vitamin D3 have been linked to increased inflammation and irritation in the digestive tract.

If you’re considering a vitamin D supplement, it’s important to consult your doctor before you start. Deena Adimoolam, MD, an endocrinologist at Summit Health in New Jersey, says, “I recommend patients get checked for vitamin D deficiency, and supplement if levels are low.” A blood level of at least 30 nanograms per millilitre is considered optimal.

Another reason to see your doctor first is to learn how to use your supplement properly. Vitamin D is fat-soluble, meaning it’s best absorbed when it’s consumed with a meal that contains some fat. You’ll also want your doctor to advise you on how much of the vitamin to take, as the necessary dosage can vary from person to person.

For generally healthy adults 19 to 70 years old, the National Institutes of Health recommends 600 international units (IU) of vitamin D per day. For adults over age 70, the recommendation increases to 800 IU. For people with certain medical conditions—such as gastrointestinal disorders that affect nutrient absorption—a doctor may recommend a higher dose. Very high doses (60,000 IU per day for several months) have been shown to cause toxicity, so it’s always wise to check with your physician about your specific needs.

It’s unlikely that vitamin D deficiency is the only cause of severe ­COVID-19 and other respiratory illnesses, but making sure that your diet contains the vitamins and nutrients your body needs should be part of your overall wellness routine.

Other important practices to support your immunity are to get the ­COVID vaccine and boosters, reduce stress, exercise regularly and make sure to get enough sleep. All these steps will help keep your immune system in good shape to fight off whatever you’re exposed to.


—With inputs by Ishani Nandi
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