A measles outbreak in Texas continues to grow, with at least 159 confirmed cases of the highly contagious disease. As public health officials work to contain the outbreak, some are concerned about messaging from Health Secretary Robert F. Kennedy Jr., who seems to elevate a nutritional supplement that does not prevent measles and can be toxic at high doses.

In an op-ed earlier this week, Kennedy highlighted vitamin A as beneficial for reducing the risk of death from measles and wrote that “good nutrition remains a best defense against most chronic and infectious illnesses.”

The health secretary then claimed in a Fox News interview that doctors in Texas are seeing good results from treating patients with the steroid budesonide, the antibiotic clarithromycin, and cod liver oil—which contains high amounts of vitamins A and D.

There are no antiviral medications to treat measles. Instead, healthcare providers focus on managing symptoms and treating bacterial infections and other complications of the disease. They sometimes give patients vitamin A as supportive care because it can be beneficial for bolstering the immune systems of sick individuals.

However, most people in the United States get plenty of vitamin A in their diet. Public health experts warn that vitamin A is ineffective at preventing measles, and taking the supplements at home could lead to overdosing.

“Vitamin A is not a treatment for measles—it’s an adjunct,” said Tina Tan, MD, a pediatric infectious disease physician and president of the Infectious Diseases Society of America. “Measles is one of the most infectious and transmissible viral illnesses anywhere, and vaccination is the tool that is the most effective at preventing someone from getting measles.”

Why Is Vitamin A Given to Children With Measles?

Vitamin A is commonly given to children in low- to middle-income countries where many people are deficient in the nutrient. The World Health Organization (WHO) recommends giving two doses of oral vitamin A to children with measles in such areas.

“We know that vitamin A plays a really critical role in maintaining a healthy immune system and supporting the function of the immune cells that help the body fight off the measles infection,” Tan said.

Most people in the U.S. get plenty of vitamin A through common foods like dairy products, eggs, fish, carrots, and sweet potatoes.

A severe measles infection can deplete a person’s vitamin A stores. If someone is hospitalized with a severe case of measles, their care team will decide if they should take more.

The Risks of Vitamin A Toxicity

Consuming too much vitamin A can be toxic. The vitamin is fat-soluble, meaning it can build up in the liver and cause problems. Children are at especially high risk for vitamin A toxicity. Overdosing on vitamin A can lead to short-term complications and long-term damage to the skin, bones, liver, brain, and more.

In an update this week, the CDC offered vitamin A dosing recommendations for healthcare providers. The agency said that “inappropriate dosing may lead to hypervitaminosis A,” a condition that can lead to liver failure and death. However, the guidance doesn’t call out those risks.

“Vitamin A, at any dose, does not protect you from measles,” James Campbell, MD, MS, vice chair of the Committee on Infectious Diseases at the American Academy of Pediatrics, said in a statement. “No one should take, and no parent should give to their child, vitamin A in hopes of preventing measles. It will not do that.”

Vaccination Remains the Best Protection Against Measles

Kennedy said healthcare providers and community leaders have a responsibility to ensure that “accurate information about vaccine safety and efficacy is disseminated,” and suggested parents consult with their healthcare providers to decide whether to immunize their children.

For decades, Kennedy has sown the disproven idea that the measles, mumps, and rubella (MMR) vaccine is linked to autism in children. In his statement this week, Kennedy acknowledged that vaccines protect both individuals and community members who cannot be vaccinated for medical reasons but falls short of urging unvaccinated people to get the shot.

“The CDC in the past has not done a good job of quantifying the risk of vaccines. We are going to do that now,” Kennedy told Fox.

Tan said that high community vaccination rates protect certain people who cannot get the shot themselves, such as infants under six months old and people with immunocompromising conditions.

“These individuals rely on everyone else to protect them. If they get measles, they’re at much higher risk of getting severe disease, being hospitalized, or dying,” she said.

Tan said that for people who can’t get vaccinated, taking a daily multivitamin can help them avoid general vitamin deficiency.

According to the CDC, even when someone is unvaccinated and exposed to measles, they can receive a vaccine within 72 hours of exposure. Certain individuals, like pregnant or immunocompromised people, can be given immunoglobulin within six days of exposure to protect them from the disease.

The MMR vaccine is typically given as a two-dose series. The first is given to infants 6 months to a year old, and the second to children 4 to 6 years old. Those who live in an area with a measles outbreak may get a shot earlier. The vaccine is about 97% effective at preventing the infection.