Original articlePeak spine and femoral neck bone mass in young women
Introduction
Osteoporosis, a disease characterized by low bone mass and porous bone structure, is a major public health problem in the United States [1]. Low bone mass is a recognized major risk factor of osteoporotic fractures [2], [3], [4], and this risk may be reduced by maximizing peak bone mass (PBM) in early life and/or minimizing the rate of bone loss in later life [5], [6].
Previous studies from our laboratory showed that 99% of peak total body bone mineral density (BMD) and bone mineral content (BMC) were observed among those aged 22 and 26, respectively [7]. Earlier investigations have reported that PBM is attained during the mid-thirties for both males and females at all skeletal sites [9], [10], [11]. A longitudinal study by Recker et al. [8] estimated that the gain in total body and spine bone mass continues through the third decade of life. The recently published results of the Fels Longitudinal Study showed that the age at which peak BMC and BMD were achieved ranged between 20 and 25, and females attained their peak earlier than males [9]. In contrast, in a longitudinal study, Theintz and colleagues [10] suggested that in healthy adolescent female subjects PBM may be attained by 16 years of age. In a cross-sectional study, Matkovic et al. [11] showed that most of the bone mass was accumulated by late adolescence or early adulthood at multiple skeletal sites. Two other cross-sectional studies also suggested that PBM at spine and femoral neck is observed in the second decade of life [12], [13]. Thus, the age of attainment of peak bone mass varies with the bone site being measured.
Calcium intake, well recognized as a factor that can affect PBM, has been inversely associated with osteoporosis risk. One observational study examining the relationship between postmenopausal BMD and childhood milk consumption revealed that higher PBM is associated with increased dietary calcium intake in childhood and adolescence [14]. Although some earlier cross-sectional studies did not find a positive association between calcium intake and bone mass [15], [16], [17], a recent cross-sectional analysis by llich et al. [18] showed that dietary calcium is one of the most significant predictors of bone mass in 456 healthy white girls aged 8 to 13 years. Additional evidence from several intervention studies also supports the importance of calcium in the accrual of bone mass during childhood and adolescence [19], [20], [21], [22], [23].
The previous study in our laboratory examining peak total body bone mass used a nonlinear statistical model which allows the estimation of age at which PBM occurred as well as the influence of other factors [7]. In the current study, this model was further developed to estimate the age at which the peak spine, femoral neck, greater trochanter, and Ward’s triangle BMD, as well as the peak spine BMC and peak spine L2–L4 bone surface area (BSA) occurred. The influence of height and weight and the effect of dietary calcium intake on the attainment of peak bone measurements at these sites were also examined. The age of the subjects covered a wide range across childhood, adolescence, and early adulthood. To our knowledge, this is the first report of an estimate of the age at which greater trochanter and Ward’s triangle occurs.
Section snippets
Subjects
Data for 300 subjects, which were baseline data from the following studies, were analyzed for this study: (1) 226 healthy white females, age 18–32, recruited for a study on bone health in young women [7]; in this exercise-intervention study, subjects were followed for 2 years for the effects of exercise on the change of their bone mass; (2) 31 healthy white females, age 13–18, recruited for a study on 3-week metabolic calcium kinetics in adolescents girls [24]; and (3) 43 healthy white females,
Results
The characteristics of all subjects are summarized in Table 1. The mean age of the subjects was 21.3 ± 5.8 years. The mean body weight and height were 59.9 ± 13.4 kg and 162.7 ± 10.8 cm, respectively.
The relationships between age and SBMD, SBMC, SBSA, FNBMD, TRBMD, and WBMD are shown in Fig. 1, Fig. 2. In all cases, age is a significant predictor of bone measures (Table 2, Table 3). The equation for age predicting SBMD is shown in Table 2 as an example of the use of the nonlinear equation.
Discussion
Improved PBM at skeletal maturity is thought to be the strongest protection against age-related bone loss and development of osteoporosis in later life. The age at which PBM is attained depends upon the site. Previously we reported that 99% peak total body BMD and total body BMC were observed at the ages of 22 and 26, respectively. In our present cross-sectional analysis, the highest level of BMD at the spine was observed in early adulthood (23.0 ± 1.4 years), and peak BMD was observed by the
Acknowledgements
Supported by National Dairy Council, and partially by NIH grant RO1-AR-39560 and RO1-AR-40553.
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