During the height of the COVID-19 pandemic last year, vitamin D was as hot as loungewear. Sales of the supplement spiked more than 34 percent and a CRN survey found 37 percent of supplement users increased their use of vitamin D.

Some studies suggested vitamin D — already known for its benefits in bone health and lowering risk of Type 1 diabetes and perhaps even cancers of the colon, prostate, esophagus, breast and lymphatic system — could provide an immune boost to prevent infections and COVID-19 complications. A recent study found a lower risk of infection among women who used vitamin D, multivitamins, probiotics and omega-3 fatty acid supplements. Other studies have found the “sunshine vitamin,” like so many other therapies tested against this never-before-seen virus, ineffective against COVID-19.

Now, in what many consider the most definitive test, researchers in Brazil found high doses of vitamin D did not help hospital patients with moderate or severe COVID-19. The study, the first of its kind, was a randomized, double-blind and placebo-controlled clinical trial with 240 volunteers conducted by scientists at the University of São Paulo’s Medical School.

Each volunteer at two local hospitals received antibiotic and anti-inflammatory medications, standard COVD-19 treatments. Then one group received a single 200,000-unit dose of vitamin D3 dissolved in peanut oil. A second group received a peanut-oil placebo. The vitamin D did not help reduce hospitalization stays, nor did it make patients less likely to be admitted to the intensive care unit or require intubation.

Now the researchers will turn to a new study that hopes to determine if a vitamin D deficiency affects the immune systems ability to fight off the virus.

But your body still needs vitamin D. Avoid a deficiency by spending 15 to 20 minutes in the sun twice a week, with 40 percent of your skin exposed. That’s all it takes, according to January 2010 research published in the International Journal of Health Sciences.

“But getting your vitamin D is a double-edged sword,” says Sharon Knight, a transplant dietitian with the Hartford Hospital Transplant Program. “Too much sun and you run the risk of skin cancer, and too little runs the risk of vitamin D deficiency.”

People through age 70 need 600 international units (or 15 mcg) per day and adults over 70 need 800 IU (or 20 mcg, or micrograms) each day, according to the National Institutes of Health.

“If your vitamin D is low,” says Knight, “your doctor will probably prescribe you a supplement and your dose will be determined per your current levels.”