In Robert F. Kennedy Jr.’s response to the US measles outbreak, he raised eyebrows by touting an idea: vitamin A.

At least 146 people have been sickened and one child has died from the disease, which is spreading in West Texas and New Mexico.

The US Health Secretary addressed the outbreak in an op-ed for Fox News. Kennedy, who has previously opposed vaccine mandates, acknowledged evidence that shows the MMR vaccine protects against disease. He did not urge Americans to get vaccinated, saying “the decision to vaccinate is a personal one.”

Kennedy then pointed to vitamin A as a potential treatment for measles, and said that a well-balanced diet “remains a best defense against most chronic and infectious illnesses.” In a subsequent Fox News interview he suggested treating measles with cod liver oil, a supplement high in vitamin A and vitamin D.

It didn’t go down well with public health workers.

Vitamin A is often touted by vaccine skeptics, including Children’s Health Defense, the anti-vaccine organization Kennedy formerly chaired.

While vitamin A is a well-studied treatment for measles, doctors and researchers told Business Insider there’s no evidence it can prevent the disease, and voiced concerns that Kennedy’s message may perpetuate a misconception that supplements could be an alternative to vaccinations.

“It’s not nearly a firm enough statement,” immunologist Andrea Love told Business Insider. “Good nutrition and vitamin A are not going to stop a measles outbreak.”

So, does vitamin A protect against measles?

Vitamin A is used to treat patients with measles in some cases. Both the World Health Organization and American Academy of Pediatrics recommend giving vitamin A to measles patients with vitamin deficiency from malnutrition.

That’s because measles can deplete the body’s supply of vitamin A, and kids deficient in vitamin A are at risk of more severe infection or complications like high fever, blindness, and even death.

Therapeutic doses of vitamin A for measles range between 15,000 to 60,000 micrograms RAE per dose — much higher than the recommended daily amount for vitamin A in your diet, which is between 700 to 900 micrograms RAE. Cod liver oil is not a standard treatment for measles.

Vitamin A is less commonly administered for measles in the US where people tend to get too much vitamin A rather than too little.

Crucially, dosing up on vitamin A supplements will not protect against a measles infection.

Christopher Sudfeld, a professor of nutrition at the Harvard T.H. Chan School of Public — and the author of a study that Kennedy cited in his Fox News op-ed — said research supports using vitamin A to reduce risk of complications from measles, but he wants people to know that supplementing it won’t protect against infection.

“The best intervention we have prevent measles is vaccination. The MMR vaccine is safe and effective for the prevention of measles,” he told BI.

Vitamin A can be toxic

Vitamin A is a major talking point for anti-vaccine advocates, who champion supplements as a protective measure, despite evidence to the contrary.

That’s why Love, the immunologist, was frustrated with Kennedy’s op-ed. She felt the resulting message could confuse readers who are already skeptical of vaccines.

“People who see this are going to pick up on the things that resonate with their beliefs,” Love told BI. “The entire wellness industry and pseudoscience landscape plays into the idea of taking control of your health.”

The problem is: it is possible to overdose on vitamin A, Love said. The nutrient is fat-soluble, which means it can build up in the tissues over time. Too much can cause problems like headaches, fatigue, joint pain, liver damage, and reduced bone density.

“My concern is people are going to start megadosing vitamin A and we’re going to see an increase in toxicity,” Love said.

The gold standard of protection against measles is widespread MMR vaccination to curtail the spread of the virus, which is incredibly infectious. A vaccinated person can be infectious for days before they show symptoms, and their breath particles can linger in the air for hours after they leave a room.

“The most effective preventive measure is vaccination, that cannot be overemphasized,” Dr. Eduardo Villamor, a professor of epidemiology at the University of Michigan School of Public Health, told Business Insider.