One in every 12 American teens (about 2.1 million) ages 12 to 17 experienced major depression in the past year, according to a report released Tuesday by the Substance Abuse and Mental Health Services Administration.

There was a large gender difference, with 12.7 percent of females and 4.6 percent of males reporting major depression. It's defined as a period of two weeks or longer of depressed mood or loss of interest or pleasure, and at least four other symptoms -- such as problems with sleep, energy, concentration and self-image -- reflecting a change in functioning.

The report, based on data from 67,706 teens who took part in the 2004 to 2006 National Surveys on Drug Use and Health, also found that 48.3 percent of teens who reported major depression said it severely impaired their ability to function in at least one of four major areas of their everyday lives, such as home life, school/work, family relationships, and social life.

Teens who reported the most severe depression-related impairment were unable to carry out normal activities on an average of 58.4 days in the past year.