One of these so-called miracle supplements is mushroom extract, which often comes in powdered form, sometimes in a blend of several different mushrooms.

There's some science behind mushrooms being good for your immunity, but there's also a lot of, um, "interesting" extrapolations from that science.

Some of those extrapolations come from companies who sell the supplements, so they are dubious at best.

So how did mushroom supplements, of all supplements, command the attention of so many people? What the heck is a mushroom, anyway? Does consuming mushrooms in supplemental forms provide any benefits? And are they safe?

Here's what the science and Registered Dietitian Abby Langer says.

What are mushroom supplements, exactly?

Mushrooms are "the fruiting bodies of macroscopic filamentous fungi that grow above the ground," according to this study in Nutrition Today, and "have been a part of the human diet and used as both food and medicine for centuries."

One reason that mushrooms may have become all wrapped up in modern disease defense is that they are a rich source of vitamin D. One of the many abilities of vitamin D is "immune function," according to the U.S. Department of Health & Human Services .

Although mushrooms supplements are advertised as containing mushrooms, supplements as a category are not strictly regulated by the U.S. Food and Drug Administration.

Are mushroom extracts good for boosting immunity?

Don't believe the hype.

"First of all, 'boosting immunity' is not something desirable," says Abby Langer, R.D. "If we boost our immune system, we get what we see in autoimmune disorders like lupus: the body attacking itself."

Instead of boosting, Langer says, "we want to aim for a balanced immune response."

While eating mushrooms, which are high in vitamin D, may help to balance your immune system, there's scant evidence to prove that consuming mushroom supplements will do the same.

In fact, one damning 2016 review published in Fungal Biology (fun read, if you ever get the chance), had these things to say about mushroom supplements.

• The worst of the advertisements for medicinal mushrooms recall the era of medical quackery
• This profitable trade provides a powerful incentive for companies to test the credulity of their customers and unsupported assertions have come to define the medicinal mushroom business.
• There is no scientific evidence supporting the use of mushroom extracts in the treatment of disease.
• Claims about the miraculous properties of medicinal mushrooms should be evaluated critically.

Are mushroom-based supplements good for preventing or treating the coronavirus COVID-19?

They are not.

"Mushroom-based supplements not only taste like deathand yes, I've tried thembut there is no human research that proves they're effective for immunity or recovery from illnessespecially COVID-19," says Langer.

"These supplements are expensive, too, so save your money and use it to eat a nourishing, well-balanced diet. That will do more for your immunity than any supplement will."

Are mushroom-based supplements dangerous?

Possibly. Consider this, from that Fungal Biology review: "With so little critical study of the benefits of medicinal mushrooms , it is alarming that the potential harm done by these natural products has been neglected."

That review lists several harmful side effects from taking mushroom extracts: inflammation of the lips, rash, and liver damage.

Plus there's this: "Dietary supplements are regulated by the FDA as food, not as drugs," according to their website . "However, many dietary supplements contain ingredients that have strong biological effects which may conflict with a medicine you are taking or a medical condition you may have."