Title

Physical activity, body composition, hip geometry and bone mass in older women

Date of Completion

January 2004

Keywords

Gerontology|Health Sciences, Nutrition

Degree

Ph.D.

Abstract

Studies investigating the relationships between physical activity and body composition with bone mineral density (BMD) in older adults have led to inconsistent results. It is also not clear how hip geometry, including hip axis length (HAL) and hip strength, relates to bone mass. The relationship between past and present physical activity, body composition, hip geometry and bone mass in over 100 postmenopausal Caucasian women was assessed over 2.5 years. Hip geometry, body composition, BMD and bone mineral content (BMC) of the dual hip, spine, total body and forearm were measured by dual X-ray absorptiometry technique. Past and present physical activity were assessed with the Allied Dunbar National Fitness Survey for older adults. Three-day dietary records were used to determine energy, protein, calcium, and sodium intake. 24-hour urine collections were used to determine urinary sodium and calcium excretion. All variables were measured once every 6 months and used to calculate cumulative averages to compare with baseline and 30-month bone values. ^ Past activity was a significant predictor of BMD in all sites. Subjects who reported a brisk or fast walking pace had significantly higher total hip BMD (p < 0.045) than subjects who reported a slow walking pace. In multiple analysis of covariance, differences in weight and lean and fat tissue accounted for 12–21% of generalized variability in BMD with weight contributing the most and fat tissue the least amount of variance. After 2.5 years subjects with more fat tissue had less bone loss in the femoral neck and forearm (p = 0.019 and 0.000, respectively) however, lean tissue did not influence BMD over time in our subjects. ^ Heavy housework, walking, weight bearing activities to the legs, total activity and activity score (based on all activities measured) were all significant predictors of BMC at various skeletal sites in multiple regression (R 2adjusted ranged from 0.292 to 0.609, p < 0.05). A longer HAL was negatively related to hip BMD, and hip strength indices were positively associated with hip BMD and physical activity (p < 0.05). ^ In conclusion, weight appears to have the strongest positive influence on BMD, with lean tissue having a bigger impact on BMD at all measured skeletal sites than fat tissue. To prevent loss in BMD, bone strength and lean tissue, brisk walking and similar activities should be maintained throughout life. ^