Final answer:
The National Institute of Mental Health reports that around 20% of American adults have some form of mental illness, with 18% potentially affected by anxiety disorders annually.
Step-by-step explanation:
According to the National Institute of Mental Health (NIMH), approximately 20 percent of adults in the United States suffer from some form of mental illness or mental disorder. Specifically, 50 million American adults are affected, of which 13 million have serious mental illness or mental disorder. Furthermore, nearly 18 percent of U.S. adults are likely to be affected by anxiety disorders in a single year, highlighting the widespread impact of mental health issues on the population.