Factors Affecting Bone Mineral Density in Elite Female Runners

• Main Author: Cartoon, Maureen E
• Format: Others
• Published: Digital Archive @ GSU 2010
• Subjects: bone mineral density; runners; physical activity; nutrition; endocrine factors; Nutrition
• Online Access: http://digitalarchive.gsu.edu/nutrition_theses/23; http://digitalarchive.gsu.edu/cgi/viewcontent.cgi?article=1013&context=nutrition_theses

Introduction: The benefits of regular exercise on skeletal health have been well-documented in terms of stimulation of bone accrual and bone maintenance. Medium-impact sports activities such as running have been demonstrated to exert site-specific enhancement of bone mass in the lower appendicular skeleton. However, elite female runners engaged in high intensity training and sports activity may also be at risk of amenorrhea and low bone mineral density (BMD) resulting from inadequate caloric intake. Purpose: To investigate the effect of intensive exercise and maintenance of adequate caloric intake on BMD in a group of elite female runners. Methods: This study represents a secondary assessment of existing data that were obtained between 1994 and 2009. Using dual-energy X-ray absorptiometry, a group of elite runners (n=11) in this study was screened in the Laboratory for Elite Athlete Performance at Georgia State University. This was a longitudinal study in which three sequential measurements of BMD, as well as fat and lean tissue body composition of each athlete took place. The average interval between measurements was 1.1 years and 2.6 years respectively. Regional BMD measurements for head, arms, legs, trunk, ribs, pelvis, and spine were assessed, as well as the value for total body BMD. The study participants also received dietary counseling emphasizing daily caloric balance and adequate calcium intake. Results: The average age of the runners increased from 24.59 (±4.41) to 28.14 (±5.94) years over the study. This was accompanied by an increase in body mass (54.98±3.54 to 56.11±4.07 kg), while height remained constant. The average body mass index (BMI) of the subjects increased from 19.34 to 19.71 kg/m2, largely due to an increase in total per cent body fat (13.97±2.96% to 16.01±4.28%). Average regional and total BMD values increased over the study period and increases were between 2 and 4%. A majority of subjects (n=7) had a BMI>19 kg/m2, while a sub-group of runners (n=4) had a BMI˂19 kg/m2. Mean trunk, pelvis and spine BMD parameters for the two BMI groups were significantly different (p˂0.05), with reduced BMD values in the lower BMI sub-group. The average T-scores associated with arm BMD were considerably lower than T-scores associated with leg BMD values in the runners. The average T-scores for leg BMD values were almost two standard deviations higher than leg BMD values for a reference population at peak bone mass. Two subjects were osteopenic, resulting in an 18% prevalence rate of osteopenia in the group of runners. Conclusions: The majority of elite runners in this study exhibited a positive trend in BMD parameters. This was reflected as increased total as well as regional BMD values. Increased body mass in addition to the activity of running positively contributed to bone mass via a weight-bearing effect. Increased adipose tissue may also have been a source of endocrine hormones such as estrogen and leptin, which exert a positive effect on bone accrual.