A recent study found a strong link between bullying during teenage years and depression later in life.

Depression has been on the rise for all age groups, but past studies linking bullying to depression struggled with significant limitations, the University of Oxford reported.

To get more solid evidence of the effects of bullying on depression, researchers conducted a longitudinal observational study that included 3,898 participants in the Avon Longitudinal Study of Parents and Children (ALSPAC). The participants completed a questionnaire about bullying at the age of 13 and were analyzed for depression at the age of 18.

Out of the 683 teens who reported being bullied more than once a week, 14.8 percent were depressed by the age of 18; of the 1,446 13-year-olds who reported being bullied one to three times over a six month period, 7.1 percent were depressed at 18 years. Only 5.5 percent of the teens who said they never experienced bullying had signs of depression later on. These findings suggest teenagers who experience frequent bullying are two times more likely to suffer from depression compared to those who were not bullied.

The most common type of bullying seen in the study was name calling (36 percent) and having belongings stolen (23 percent). Between 41 percent and 74 percent of bullied teens never told a teacher, and between 24 percent and 51 percent never told a parent; up to 75 percent did report physical bullying to an adult.

The researchers believe the findings show about 30 percent of depression in young adulthood can be linked to bullying during teenage years.

"While this is an observational study and no definitive conclusions can be drawn about cause and effect, they say that interventions to reduce bullying in schools could reduce depression in later life," the researchers said.

The findings were reported in a recent edition of the British Medical Journal.