COVID caused more than 20 million Americans to lose their ability to smell and taste, and at least 25% haven't regained those vital senses, a new study says.

Survey responses from nearly 29,700 adults also show a correlation between more severe COVID infection and taste and smell loss, researchers reported recently in the journal The Laryngoscope.

"The value of this study is that we are highlighting a group of people who have been a bit neglected," said study co-author Dr. Neil Bhattacharyya, a professor of otolaryngology at Massachusetts Eye and Ear.

"Losing your sense of smell or taste isn't as benign as you may think. It can lead to decreased eating for pleasure and, in more extreme cases, it can lead to depression and weight loss," he added in a journal news release.

One motivation for the study was a patient who lost 50 pounds due to his loss of smell, Bhattacharyya said.

"The patient wasn't eating and became very sick and very depressed because of the loss of smell," Bhattacharyya said. "When you hear about COVID-related smell loss, you think most people get it back and are fine. But there is a substantial number of people who don't recover it."

Using data from the 2021 National Health Interview Survey, the researchers found that about 60% of participants infected with COVID had a loss of smell and about 58% experienced a loss of taste.

Around 72% of patients fully recovered their sense of smell, but others were less fortunate. Twenty-four percent only had a partial recovery and more than 3% had no recovery of their sense of smell at all.

Of those who experienced a loss of taste, about three-quarters fully recovered the sense, while 20% only partially recovered their sense of taste and more than 2% did not regain it at all.

The researchers also found that as COVID symptoms increased, the percentage of patients with smell or taste loss also increased. The odds of smell and taste recovery also decreased with severe COVID symptoms.

The study only included data from 2021. The researchers say many more Americans are likely unable to smell or taste in the aftermath of their COVID infection.