Prevalence of and Traits Associated With Low BMD Among Female Adolescents
Prevalence of and Traits Associated With Low BMD Among Female Adolescents
Purpose: Identify the prevalence of and traits that may increase the risk of low bone mineral density (BMD) among 93 female adolescent competitive endurance runners.
Methods: Participants were 93 high school runners, ages 13-18 yr, from southern California. Eating attitudes and behaviors were assessed using the Eating Disorder Examination Questionnaire (EDE-Q). Menstrual and sports participation history were evaluated using an interviewer-assisted, self-report questionnaire. Bone mineral density (BMD) of the spine (L1-L4), total hip, and total body were measured by dual-energy x-ray absorptiometry. The -2 and -1 BMD age-matched, gender-specific z-score cutoffs were used to categorize girls as having low bone mass for age.
Results: Among the female runners, 11.8% and 28% met the -2 and -1 BMD z-score cutoffs, respectively, whereas 25.8% reported menstrual irregularity (MI). Total hip BMD, lumbar spine BMD, and lumbar spine BMD z-score were significantly lower in runners with MI after adjusting for body mass index (BMI) and lean tissue mass. Runners that participated in five or more compared with three seasons of endurance running exhibited a significantly lower total body and lumbar spine BMD z-score after adjusting for BMI, lean tissue mass, and number of menstrual cycles in the past year. Multiple regression analysis indicated that MI, participation in five or more seasons of endurance running, BMI, and lean tissue mass were independent predictors of low BMD.
Conclusion: Female adolescent endurance runners may represent a population with an increased risk of low bone mass. Future studies are necessary to further understand the factors contributing to low bone mass in young runners and to identify behavioral strategies that will promote optimal bone mineral accumulation during the adolescent years.
According to the new ACSM position stand, the female athlete triad is now defined as a condition involving three interrelated spectrums, namely, energy availability (defined as energy intake minus exercise energy expenditure), menstrual function, and bone mineral density (BMD), with the athlete exhibiting the full triad presenting chronic low energy availability (LEA), functional hypothalamic amenorrhea, and osteopenia/osteoporosis. Although a female competitor participating in any sport may develop the conditions characteristic of the triad, previous studies have reported elevated prevalence estimates of menstrual irregularity (MI) and low BMD among collegiate and postcollegiate endurance runners. Laboratory studies have identified a direct effect of LEA on reducing estradiol, lowering bone deposition, and increasing bone resorption. Therefore, the elevated prevalence of MI and low BMD among young adult runners may be due, in part, to the high energy demands of running and the tendency of competitive runners to inadequately replenish calories expended after a training session or competitive event.
Adolescence is a period of rapid bone mineral accumulation where, under normal conditions, approximately 40-50% of adult bone mineral content (BMC) is accumulated and 90% of overall BMC is achieved by age 16.9 ± 1.3 yr. Because LEA has been reported to disrupt hormones that regulate bone metabolism and alter markers of bone turnover among young adult women, a chronic low-energy state occurring during adolescence may contribute to an inadequate bone mineral accumulation and a low peak bone mass. This effect may by irreversible and may also increase the risk of an individual developing osteopenia or osteoporosis. Furthermore, adolescence marks the developmental stage where (except during pregnancy and lactation) energy needs are highest. Consequently, female adolescent endurance runners may represent a population at risk for developing LEA and may represent a group where LEA may have the most detrimental, long-term effects.
Most studies that have reported on the prevalence of individual or multiple components of the triad have examined collegiate and postcollegiate, recreational and elite athletes. Few reports exist that provide important information on the prevalence of low BMD or traits associated with low bone mass in adolescent runners. Identifying and understanding predictors of low bone mass among adolescent runners is important because these behaviors may be limiting bone mineral accumulation, which may lead to a reduced peak bone mass. Therefore, the purpose of our study was to determine the prevalence of and traits that may increase the risk of low BMD in a large sample of female adolescent endurance runners.
Abstract and Introduction
Abstract
Purpose: Identify the prevalence of and traits that may increase the risk of low bone mineral density (BMD) among 93 female adolescent competitive endurance runners.
Methods: Participants were 93 high school runners, ages 13-18 yr, from southern California. Eating attitudes and behaviors were assessed using the Eating Disorder Examination Questionnaire (EDE-Q). Menstrual and sports participation history were evaluated using an interviewer-assisted, self-report questionnaire. Bone mineral density (BMD) of the spine (L1-L4), total hip, and total body were measured by dual-energy x-ray absorptiometry. The -2 and -1 BMD age-matched, gender-specific z-score cutoffs were used to categorize girls as having low bone mass for age.
Results: Among the female runners, 11.8% and 28% met the -2 and -1 BMD z-score cutoffs, respectively, whereas 25.8% reported menstrual irregularity (MI). Total hip BMD, lumbar spine BMD, and lumbar spine BMD z-score were significantly lower in runners with MI after adjusting for body mass index (BMI) and lean tissue mass. Runners that participated in five or more compared with three seasons of endurance running exhibited a significantly lower total body and lumbar spine BMD z-score after adjusting for BMI, lean tissue mass, and number of menstrual cycles in the past year. Multiple regression analysis indicated that MI, participation in five or more seasons of endurance running, BMI, and lean tissue mass were independent predictors of low BMD.
Conclusion: Female adolescent endurance runners may represent a population with an increased risk of low bone mass. Future studies are necessary to further understand the factors contributing to low bone mass in young runners and to identify behavioral strategies that will promote optimal bone mineral accumulation during the adolescent years.
Introduction
According to the new ACSM position stand, the female athlete triad is now defined as a condition involving three interrelated spectrums, namely, energy availability (defined as energy intake minus exercise energy expenditure), menstrual function, and bone mineral density (BMD), with the athlete exhibiting the full triad presenting chronic low energy availability (LEA), functional hypothalamic amenorrhea, and osteopenia/osteoporosis. Although a female competitor participating in any sport may develop the conditions characteristic of the triad, previous studies have reported elevated prevalence estimates of menstrual irregularity (MI) and low BMD among collegiate and postcollegiate endurance runners. Laboratory studies have identified a direct effect of LEA on reducing estradiol, lowering bone deposition, and increasing bone resorption. Therefore, the elevated prevalence of MI and low BMD among young adult runners may be due, in part, to the high energy demands of running and the tendency of competitive runners to inadequately replenish calories expended after a training session or competitive event.
Adolescence is a period of rapid bone mineral accumulation where, under normal conditions, approximately 40-50% of adult bone mineral content (BMC) is accumulated and 90% of overall BMC is achieved by age 16.9 ± 1.3 yr. Because LEA has been reported to disrupt hormones that regulate bone metabolism and alter markers of bone turnover among young adult women, a chronic low-energy state occurring during adolescence may contribute to an inadequate bone mineral accumulation and a low peak bone mass. This effect may by irreversible and may also increase the risk of an individual developing osteopenia or osteoporosis. Furthermore, adolescence marks the developmental stage where (except during pregnancy and lactation) energy needs are highest. Consequently, female adolescent endurance runners may represent a population at risk for developing LEA and may represent a group where LEA may have the most detrimental, long-term effects.
Most studies that have reported on the prevalence of individual or multiple components of the triad have examined collegiate and postcollegiate, recreational and elite athletes. Few reports exist that provide important information on the prevalence of low BMD or traits associated with low bone mass in adolescent runners. Identifying and understanding predictors of low bone mass among adolescent runners is important because these behaviors may be limiting bone mineral accumulation, which may lead to a reduced peak bone mass. Therefore, the purpose of our study was to determine the prevalence of and traits that may increase the risk of low BMD in a large sample of female adolescent endurance runners.
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