Bone mineral density and total body bone mineral content in 18- to 22-year-old women☆
Introduction
Twenty-six million American women are at risk for fracture due to osteopenia and osteoporosis [19]. Minor trauma in osteoporotic individuals results in 1.5 million fractures annually [25]. Hip fracture alone results in over 250,000 admissions to United States hospitals each year [24] at a total cost of 13.8 billion dollars annually [25]. With the aging US population, the numbers of hip fractures will likely increase [5]. Fractures in the elderly are especially debilitating and are associated with significant co-morbidity and mortality. The consequences of these injuries contribute to rising health care costs and decreased quality of life.
The current major public health strategy to prevent osteoporosis is to develop opportunities to maximize peak bone mass in teenage boys and girls, and into early adulthood, because evidence suggests that osteoporosis is more effectively prevented than treated. Currently, no general consensus exists concerning the age at which peak bone mass (PBM) is achieved and longitudinal data on change in bone mass among young adults is limited. Bone accretion was generally thought to conclude with cessation of linear growth and some recent studies support this theory [4], [31], [32], [38]. In a prospective study by Kroger et al. [14], bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) twice with a 1-year interval in male and female adolescents ranging in age from 7 to 20. The most dramatic changes were observed in the increased bone mineral content (BMC) and BMD in the spine and femoral neck of both sexes. In the young girls, the greatest increase in BMD and BMC occurred during a 2-year period surrounding menarche, while the males had rapid bone accretion over a 4-year period between ages 13 and 17. By age 20, bone accretion had diminished markedly in both sexes. The longer period of rapid, linear growth observed in males, results in larger bone volume and cortical thickness, while actual trabecular density is similar to that of females. These factors appeared to account for most of the difference in total bone mineral content (TBMC) between genders. A second study by Slosman et al. [33] measured BMD at baseline and 1 year later in 20–35 year old males and females to examine the relationship of age to peak bone mass. There were no significant changes in BMC or BMD despite precise measurement by DXA, and the authors concluded that no bone accretion occurs during the third decade. Other cross-sectional [27], [34] and longitudinal studies [1], [23], [26], [27] report that bone accretion extends into the third decade of life.
The purpose of this study is to report the normal reference mean TBMC and BMD using DXA in young, healthy 18-year-old women at entry to the United States Naval Academy (USNA) and followed annually until their graduation.
Section snippets
Methods
Two hundred thirty-five (235) female midshipmen (midn) from three USNA graduating classes were recruited to voluntary participation in this study and provided informed consent as approved by the Committee for the Protection of Human Subjects at the National Naval Medical Center. Seventy-one (71) of the 235 female subjects in this study were excluded for the following reasons:
- (a)
Eighteen (18) subjects, were diagnosed with a lower extremity stress reaction or stress fracture during the study,
- (b)
Ten
Results
The 164 female midn in this study were 18.5 ± 0.3 years old at the time of their first DXA appointment. Their final DXA appointment occurred 3.6 years later in the spring of their 4th year at USNA.
Midshipmen height was 166.4 ± 0.56 cm at entry and remained unchanged over the study period. Body mass at entry was 60.7 ± 0.57 kg and the body mass index (BMI) (body mass in kg/(height in m)2) was 21.9 ± 0.17. By the end of the study body mass had risen 4.3% to 63.3 ± 0.60 kg (P < 0.001) and BMI 4.1%
Discussion
We followed 164 healthy, physically active young Caucasian women for 3.6 years, measuring TBMC and BMD at the lumbar spine, hip, and distal tibia approximately annually. We report the normative data and change over time in BMD and TBMC for these 18- to 22-year-old women. The primary finding of this study is that young women continue to accrue bone until at least age 22 years, following the cessation of linear growth, and in the absence of significant changes in regional bone area. Our
Acknowledgements
The Chief, Navy Bureau of Medicine and Surgery, Washington, D.C., Clinical Investigation Program Sponsored this study #B91-067. Funding for this research was provided by the Office of Naval Research.
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The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, nor the U.S. Government.