As a measles outbreak spreads across U.S., doctors are now seeing a new and unexpected danger: Children getting sick from taking too much vitamin A.

At Covenant Children’s Hospital in Lubbock, Texas, several unvaccinated children showed signs of liver problems after taking large amounts of vitamin A, according to Dr. Lara Johnson, the hospital’s chief medical officer.

U.S. Department of Health and Human Services Secretary Robert F. Kennedy Jr. has promoted vitamin A during the outbreak, even suggesting it might help prevent measles. But doctors say this isn’t true.

“If people have the mistaken impression that you have an either-or choice of MMR vaccine or vitamin A, you’re going to get a lot of kids unnecessarily infected with measles. That’s a problem, especially during an epidemic,” Dr. Peter Hotez, co-director of the Texas Children’s Hospital Center for Vaccine Development and dean of the National School of Tropical Medicine at Baylor College of Medicine, told CNN. “And second, you have this unregulated medicine in terms of doses being given and potential toxicities.”

The measles, mumps and rubella (MMR) vaccine is the only proven way to prevent measles. It is 97% effective after two doses. Kennedy has said he encourages vaccines, but considers vaccination a personal choice.

Vitamin A can be helpful for people with measles when given in the right dose by a doctor. But taking too much, especially without medical supervision, can be dangerous.

Vitamin A is fat-soluble and can build up in the body. This can lead to dry skin, blurry vision, bone problems and liver damage. In pregnant women, it can even cause birth defects.

Dr. Lesley Motheral, a pediatrician in Lubbock, said kids in Texas are generally well-nourished and don’t need extra vitamin A.

“Recovery for patients with acute toxicity can be rapid when the vitamin is discontinued,” Motheral said. “Sadly, some of the more serious problems with vitamin A toxicity are not always reversible.”

The Council for Responsible Nutrition (CRN), a group representing supplement makers, also warned parents not to give their children high doses of vitamin A. 

“While vitamin A plays an important role in supporting overall immune function, research hasn’t established its effectiveness in preventing measles infection. CRN is concerned about reports of high-dose vitamin A being used inappropriately, especially in children,” it said in a statement.

Johnson said some parents may be following questionable advice from social media or health influencers.

“It’s coming out of the health and wellness … influencer industry that downplays the importance of vaccines and tries to promote various spectacular cures like ivermectin or hydroxychloroquine or vitamin A,” Hotez added.

In a recent interview with Fox News, Kennedy promoted a treatment plan that includes vitamin A, a steroid, an antibiotic and cod liver oil, but doctors say there’s little to no proof this works for measles.

The measles outbreak has now affected at least 378 people in 17 states, from Texas and New Mexico to Vermont, New York and Washington.