In the largest population-based study to explore the use of hormones and supplements, body image, and media influences, 8 percent of all girls and 12 percent of all boys reported using products in the past year to improve their appearance, muscle mass, or strength. Nearly 5 percent of boys and 2 percent of girls used such products at least weekly. About 30 percent of both sexes reported thinking frequently about wanting more toned or defined muscles; after adjustment for other factors, boys with such thoughts were 60 percent more likely than their peers, and girls twice as likely, to use supplements at least weekly.

The most commonly used products were protein powders and shakes. Others, used predominantly by boys, included creatine, amino acids, the amino-acid metabolite HMB, the hormone dehydroepiandrosterone (DHEA), growth hormone, and anabolic steroids.

"The Internet is full of sites where these substances can be purchased, and many are advertised in popular health and fitness magazines with covers like "Great abs in 5 minutes a day,'" says Dr. Alison Field, an epidemiologist in the Division of Adolescent Medicine and the Department of Psychiatry at Children's Hospital Boston and the study's first author. "Protein powders are probably relatively safe, but steroids have well-known side effects, and some of the other products may not be so benign."

Anabolic steroids have the most serious health effects, including testicular atrophy, impotence, liver and kidney damage, an increased risk for heart disease, and the widely reported "roid rage" (uncontrolled aggression). The safety of creatine, DHEA, and other products purported to increase muscle mass and tone has been questioned and isn't well known.

"Most of us in adolescent medicine think it's best to stay away from these products altogether," Field says.

The survey, of adolescents aged 12 to 18, was done in 1999 as part of the Growing Up Today Study (GUTS), which involves children of nurses enrolled in the Nurses' Health Study based at Brigham and Women's Hospital. GUTS was co-founded by Field and Dr. Graham Colditz and colleagues of Harvard Medical School and the Harvard School of Public Health.

The findings also indicate that the media have a strong influence on adolescent supplement use and that body-image concerns are well established among boys:

Girls who said they wanted to look like women in the movies, magazines, or on TV were more than twice as likely as their peers to use supplements at least weekly to increase muscle mass or definition. Twenty-one percent of girls with this desire had used at least one such product in the past year.

Boys who read men's, fashion, or health/fitness magazines were more than twice as likely as their peers to use supplements at least weekly to increase muscle mass or definition. Twenty-nine percent of boys reading these magazines had used at least one product in the past year.

Boys wanting to gain weight were three times more likely than their peers to use supplements at least weekly; in girls, the likelihood was more than quadrupled.

Weight lifting and playing football were linked to increased use of supplements -- particularly creatine, amino acids, DHEA, growth hormone, and steroids. Whether such use was self-driven, peer-driven, or coach-driven is unknown.

"More and more media images show people with sculpted physiques. It used to just be scantily-clad women, but now, you see more and more of images of men with physiques are that impossible for most people to attain" says Field, who also has appointments at Brigham and Women's Hospital and Harvard Medical School. "Girls' concerns about their bodies are well known, but I don't think it's on parents' radar screens that their sons might have body concerns -- 'I'm not big enough, I'm not strong enough, I'm not buff enough.'"

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