Nearly 1 in 12 Americans struggles with depression, with middle-aged women suffering at the highest rate, yet only about a third of those with depression are seeking professional help, a study indicates.

Women aged 40 to 59 display the highest rate of depression, 12.3 percent, of any gender and age group in the U.S, and women showed higher rates of depression than men did in all age groups, the Centers for Disease Control and Prevention study found.

However, in the years between 2009 and 2012, around two-thirds of people with depression did not avail themselves of professional medical help, the researchers said.

"Not enough people are getting appropriate treatment for depression," says epidemiologist and study leader Laura Pratt at the CDC's National Center for Health Statistics.

Depression can go beyond its effects on people's mood; it can also impair cognitive functions including decision-making and concentration, and can even impact their physical health.

Left untreated, severe depression can lead to problems at work, within a family and in social situations.

Previous studies have suggested a combination of psychological and medical therapies is the most effective treatment for more severe cases of depression.

"People with severe depression should be getting psychotherapy," Pratt said. "Some might need complicated medication regimens, which psychiatrists are better equipped to do, which makes it even more concerning that only 35 percent of people with severe depression have seen a mental health professional."

The statistics in the CDC report are consistent with those found in previous studies, which is not encouraging, says Simon Rego, head of psychology training at the Albert Einstein College of Medicine in New York City.

"Much of the information is not new or surprising," he says. "What's disappointing, however, is the fact that the rates of treatment have remained so low."

The good news, he notes, is that there are now highly effective treatments available, including psychological interventions such as cognitive behavioral therapy and improved drugs to treat depression medically.

Pratt says she hopes the report will raise awareness of the prevalence of depression.

"It's serious, it really affects your life and we need to figure out a way to get people treated appropriately," she says.

That's something Rego says he agrees with.

"Clearly much more work needs to be done to educate the public on the symptoms of depression, the major impact it can have on one's functioning, and the benefits of seeking an appropriately trained mental health professional," he says.