Does vitamin D “support immune health,” as some supplement labels claim?

Scientists randomly assigned 5,979 people to receive either a daily supplement with 800 IU or 3,200 IU of vitamin D or no supplement.

After six months, the three groups didn’t differ in the incidence of colds, Covid-19, or other acute respiratory infections or in hospitalizations from those infections. (During those six months, in early 2021, 89 percent of the participants got at least one Covid-19 vaccine.)

And in a trial on 34,601 adults, a daily teaspoon of cod liver oil (which contained 400 IU of vitamin D) for five months had no impact on the number of Covid-19 or other respiratory infections.

(Both trials were partly funded by vitamin companies.)

What to do

Don’t expect vitamin D supplements to prevent acute respiratory infections.