Dr. Mark Hyman most recently expressed those skeptical views in a book he co-wrote with Robert Kennedy Jr. titled: “Thimerosal: Let the Science Speak.”

In the book and in a recent TV appearance on “Dr. Oz,” Hyman and Kennedy expressed concern that the mercury in thimerosal, a preservative used in some vaccines, is associated with autism, developmental delays and certain illnesses.

That belief is considered controversial in the medical community.

While Hyman has claimed that he is not a so-called “anti-vaxxer,” he has questioned whether people should get the flu vaccine and has supported the theory that the measles, mumps and rubella vaccine (MMR) can cause autism and other issues.