Aluminum in childhood vaccines is a target of vaccine skeptics, who blame the ingredient on myriad health concerns. But a study of more than 1 million people, published Monday in the Annals of Internal Medicine, found no link between aluminum in vaccines and an increased risk of 50 chronic conditions, including autoimmune diseases, allergies and autism.

Health and Human Services Secretary Robert F. Kennedy Jr., who has spread vaccine misinformation for years, said on a podcast in 2024 that aluminum in vaccines is “extremely neurotoxic.” (An HHS spokesperson did not respond to a request for comment.)

Senior study author Anders Hviid said that, as a parent, he understood the concerns about vaccine safety.

“Our study addresses many of these concerns and provides clear and robust evidence for the safety of childhood vaccines. This is evidence that parents need to make the best choices for the health of their children,” said Hviid, who is a professor and the head of epidemiology research at Statens Serum Institut, a sector of the Danish Ministry of Health focused on combating and preventing infectious diseases.