More than 45 million Americans, or 20 percent of U.S. adults, had some form of mental illness last year, and 11 million had a serious illness, U.S. government researchers reported on Thursday.
Young adults aged 18 to 25 had the highest level of mental illness at 30 percent, while those aged 50 and older had the lowest, with 13.7 percent, said the report by the Substance Abuse and Mental Health Services Administration or SAMHSA.
The rate, slightly higher than last year's 19.5 percent figure, reflected increasing depression, especially among the unemployed, SAMHSA, part of the National Institutes of Health, said.
"Too many Americans are not getting the help they need and opportunities to prevent and intervene early are being missed," Pamela Hyde, SAMHSA's administrator, said in a statement.
"The consequences for individuals, families and communities can be devastating. If left untreated mental illnesses can result in disability, substance abuse, suicides, lost productivity, and family discord."
The 2009 mental health survey hints at the impact of record unemployment rates, which last year hit a 25-year high as struggling employers slashed jobs to cope with a weak economy.
For many, lost employment meant loss of health insurance, leaving many of the nation's mentally ill unable to get treatment.
According to the survey, 6.1 million adults last year had a mental health need that went untreated, and 42.5 percent said it was because they could not afford it.
It found 14.8 million Americans had major depression last year, and 10 percent of the jobless did, compared with 7.5 of retired people or those not in the job force, 7.3 percent who worked part time and 5.4 percent who worked full time.
Only 64 percent of adults aged 18 or older with major depression were treated last year, compared with 71 percent a year ago.
Being jobless also increased the risk of suicide.
Adults who were unemployed last year were twice as likely to have serious thoughts of suicide as people who were fully employed, with 6.6 percent of the unemployed considering suicide, compared with 3.1 percent of those who were working.
The survey also found that 23.8 percent of women had some form of mental illness, compared with 15.6 percent of men.