U.S. Health Secretary Robert F. Kennedy Jr. announced on Wednesday that he is planning new studies to identify environmental contributors to autism that he links to its rising prevalence in the country.

At Kennedy's first press conference since he became head of the U.S. Department of Health and Human Services, he said the studies will look at mold, air, water, food, medicine, ultrasounds, and parental risk factors such as age, obesity and diabetes.

The causes of autism are unclear. Experts say it likely results from a combination of genetic and environmental factors, and that the increase in diagnoses in the U.S. is partly but not wholly due to better awareness and a broader range of characteristics used to describe the condition.

Kennedy was speaking after the release on Tuesday of a government data analysis showing prevalence of autism spectrum disorder in the U.S. among 8-year-olds in 2022 was 32.2 per 1,000, or 1 in every 31, up from 1 in 36 in 2020 and 1 in 44 in 2018. The data was published in the U.S. Centers for Disease Control and Prevention's weekly report.

On Wednesday, Kennedy said he would move monitoring of autism rates to the newly created Administration for a Healthy America, which is part of HHS.

Kennedy, who has long promoted a debunked link between vaccines and autism, last week set a September deadline for the U.S. National Institutes of Health to determine the cause behind the rise in U.S. autism rates. On Wednesday, he said they would have "some of the answers" by September.

Rising rates of autism in the United States since 2000 have intensified public concern over what might be contributing to its prevalence.