One in eight middle-age women in the United States has depression, a new report finds.

This means that women ages 40 to 59 have the highest rate of depression (12.3 percent) of any group based on age and gender in the U.S., according to the report from the Centers for Disease Control and Prevention.

In all other age groups as well, women had higher rates of depression than men did. Among Americans ages 12 and older, 9.5 percent of females and 5.6 percent of males had moderate or severe depression during the previous two-week period, according to the report, which is based on data gathered from 2009 through 2012.

Depression is a serious medical condition that can affect not only people's mood, but also their cognitive functions, such as concentration and decision-making abilities, and even their physical well-being. The symptoms can range from mild to severe.[7 Ways Depression Differs in Men and Women]

Although there are various approaches for treating depression, studies have shown that a combination of medication and psychological therapy may work best to treat severe depression. However, many people with depression do not get any treatment, studies have shown. Only 35 percent of people who had severe depression reported having seen a mental health professional in the past year, the researchers said in the new report.

In the study, the researchers evaluated whether the participants had depression by conducting in-person interviews and questioning about symptoms of depression.

Depression can affect both the personal and professional areas of a person's life. In the study, nearly 90 percent of people with severe depressive symptoms reported having difficulty at home, with work or in their social activities. Almost half of the people who had mild depression reported having such difficulties.

The report also found that 15 percent of people who live in poverty had depression, meaning that they were more than twice as likely to have depression as people living above the federal poverty level, who have a depression rate of 6.2 percent.

The rate of depression generally increased with age, with 5.7 percent of youth ages 12 to 17 reporting having the condition, but 9.8 percent of adults ages 40 to 59 saying the same. However, people ages 60 and over had a lower rate of depression (5.4 percent) than people in other age groups.

These estimated depression rates may even be lower than the actual rates. That's because people with depression might be slightly more likely to decline to participate in the surveys used for the report, the researchers said. Moreover, people who live in mental health facilities, who may have higher rates of depression, were not included in the study, and people who are being successfully treated for depression were not identified as depressed

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