Nearly half of all Americans will suffer some form of mental health problem during their lifetime, the U.S. Centers for Disease Control and Prevention reports, stating must be done to help them.

The new government report was based on data collected and tallied on years of country-wide surveys.

It was published on Sept. 2 in the CDC's Morbidity and Mortality Weekly Report.

The CDC research found that 25 percent of American adults reported having a mental illness the previous year. The additional costs associated with treating those Americans in 2002 was $300 billion.

There are unacceptably high levels of mental illness in the United States, said Ileana Arias, principal deputy director of the CDC. Arias said the high cost includes care for the illness and lost productivity.

It still isn't clear why so many Americans suffer from mental illness.

This is an issue that needs to be addressed, Arias said, not only because of the illness itself, but because mental disorders are associated with other chronic illnesses such as heart disease and cancer.

In 2009, some 11 million people, or 5 percent of the population, experienced some kind of mental illness that affected their ability to function. A staggering 8.4 million contemplated suicide in the past year, and 2.2 million actually made plans to kill themselves.

One million attempted suicide, according the study.

While having a psychiatric illness can be tough, there's also the stigma surrounding these diagnoses, which can be an additional burden, experts said.

Many people with mental illness hide their problems from others, some do so out of embarrassment.

Under-diagnosis and under-treatment are still big problems in the U.S., according to mental health experts

Mental illness is frequently seen as a moral issue or an issue of weakness, Arias said. It is a condition no different from cancer or other chronic diseases. People need to accept the difficulties they are having and avail themselves of the resources that are available.