(NewsNation) — More than 3 million Americans are estimated to suffer from chronic fatigue syndrome, according to a new analysis from the Centers for Disease Control and Prevention.

The estimate is based on data collected in the 2021-2022 National Health Interview Survey.

Here’s some key facts about the health condition:

What is chronic fatigue syndrome?

The CDC defines the condition as a “complex, multisystem illness characterized by activity-limiting fatigue, worsening of symptoms after activity, and other symptoms.”

People are often not able to do their usual activities, the CDC says, and they may be confined to bed at times.

Chronic fatigue syndrome can result in severe fatigue and sleep problems, and its symptoms may worsen as people try to do as much as they want or need to do. That can lead to another condition known as post-exertional malaise.

Other symptoms include trouble concentrating, pain and dizziness.

How many people does it affect?

The latest survey from the CDC found that 1.3% of U.S. adults had chronic fatigue syndrome. With a total adult population of about 258 million, that means up to 3.3 million could be affected.

Another study by the Institute of Medicine estimated between 836,000 to 2.5 millions have the medical condition.

In the CDC survey, participants were asked if a doctor or other health care professional had ever told them they had myalgic encephalomyelitis or chronic fatigue syndrome, and whether they still have it. The report, which survived 57,000 U.S. adults in 2021 and 2022, revealed about 1.3% said yes to both questions.

The survey found women are more likely than men to have chronic fatigue syndrome, with 1.7% of women experiencing it compared to 0.9% of men.

The percentage of those with the condition increased with age through ages 60-69 before declining among those age 70 and older.

The condition also is more likely to affect white non-Hispanic adults, 1.5% of whom reported having it. The second likeliest group to have it is Black non-Hispanic adults at 1.2%, followed by Hispanic adults at 0.8% and then Asian non-Hispanic adults at 0.7%.

It was also more prevalent in those with a lower family income and those living in more rural areas.

What are doctors saying about it?

Dr. Elizabeth Unger, one of the report’s co-authors, said the survey data shows the condition “is not a rare illness.”

Doctors have not been able to pin down a cause, although research suggests it is a body’s prolonged overreaction to an infection or some other jolt to the immune system.

Dr. Tom Pitts said he’d start by conducting a sleep study for patients who are experiencing fatigue instead of immediately diagnosing them with chronic fatigue syndrome.

“I always want to make sure their sleep is not interrupted by inflammation, movements, problems that are not getting into REM sleep; that’s the number one cause of daytime fatigue,” Pitts said on NewsNation’s “Morning In America.” “Then, I would run a complete set of labs, scan relevant things history, and physical are vital.”

Dr. Daniel Clauw, director of the University of Michigan’s Chronic Pain and Fatigue Research Center, told the Associated Press that experts believe only a fraction of the people with chronic fatigue syndrome are diagnosed.

“It’s never, in the U.S., become a clinically popular diagnosis to give because there’s no drugs approved for it. There’s no treatment guidelines for it,” Clauw said.

Is there a treatment?

According to the CDC, there is no cure or approved treatment for the condition itself, but patients can manage or treat some symptoms.

“Patients, their families and health care providers need to work together to decide which symptom causes the most problems. This should be treated first,” the CDC says. “Patients, families, and healthcare providers should discuss the possible benefits and harms of any treatment plans, including medicines and other therapies.”

To help with sleep problems, the CDC suggests over-the-counter sleep products, or a doctor-prescribed sleep medication. Good sleep habits may also help.

Treatments for patients experiencing depression or anxiety may possibly include antidepressants, though the CDC advises doctors to use caution when prescribing medication, as some drugs may worsen symptoms.

Professional counseling, a balanced diet, nutritional supplements and complementary therapies are suggested for those who wish not to take medication.

NewsNation digital producer Taylor Delandro and the Associated Press contributed to this report.