About one in 20 teenagers have used steroids to increase their muscle mass, a new study suggests.

In addition, more than one-third of boys and one-fifth of girls said they had used protein shakes or powders to increase their muscles, while between five and 10 percent used non-steroid substances to bulk up.

The study, published in the journal Pediatrics, included almost 2,800 students in middle and high schools in Minnesota. Most of the students had engaged in at least one muscle-building activity in the previous year. Up to one-third used what researchers considered unhealthy ways to increase their muscle mass, such as taking steroids or other muscle-building substances, or drinking too many protein shakes or engaging in excessive weight-lifting.

The study found steroid use was equally common among students who were athletes and those who were not.

"Really the pressure to start using (steroids) is in high school," Dr. Linn Goldberg of the Oregon Health & Science University, who was not involved in the study, told Reuters. "You get the influence of older teens in high school, so when you're a 14-year-old that comes in, you have 17-year-olds who are the seniors, and they can have great influence as you progress into the next stage of your athletic career."

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