Controlled trial of weight bearing exercise in older women in relation to bone density and falls

Introduction

Studies of the effects of different exercise programmes on bone in postmenopausal women have produced different conclusions, but few have targeted elderly women specifically.1 We report a controlled trial of weight bearing exercise in this clinically important population.

Methods and results

The study was approved by the local ethics committee. We recruited volunteers by advertising in the local press. After excluding subjects with conditions or drug treatment likely to affect bone, we randomly allocated 118 volunteers (mean age 64.5 (range 60-73) years) to either a group taking calcium supplementation (1000 mg calcium daily, as calcium carbonate) or to an exercise group taking the same calcium supplementation. We monitored compliance with calcium by a tablet count every six months.

We asked volunteers in the calcium group taking exercise to attend the University of Dundee's exercise class for people aged over 60 three times weekly for each of three 10 week terms a year for the two years of the study. Each session lasted for 45 minutes and involved weight bearing exercise to music.2

The bone mineral content of the non-dominant distal forearm was measured with a Molsgaard single photon absorptiometer, and lumbar vertebral bone mineral density was measured by quantitative computed tomography both at entry to the study and at two years.

We found no significant differences between the groups at baseline. In all, 12 subjects dropped out from the calcium group and 14 from the calcium group taking exercise, leaving 92 subjects (78%) who completed the two year project. Attendance at the exercise classes for the two years of the study ranged from 46% to 100%, with a mean of 76% of classes attended. The average compliance, based on tablet counts, was 96.9% (range 80% to 100%) in both groups. The range of drug treatment, alcohol intake, total energy intake, and dietary calcium intake was similar in both groups and stable during the study.

The percentage change in bone mineral content and bone mineral density in two years was calculated for each individual; in the ultradistal forearm the change in bone mineral content showed a modest significant increase in the calcium group taking exercise compared with a decline in the calcium group (table 1)). Only two fractures were recorded during the two year study, both in the calcium group.

Twenty one women in the calcium group had falls (31 falls in all), compared with 13 women in the calcium group taking exercise (15 falls in all). The difference between the groups in the number of women falling during the whole two year period was not significant (P=0.158), but between 12 months and 18 months into the study the difference was significant (P=0.011).

Comment

We found a modest additional effect of exercise on the bone density of the ultradistal forearm among women aged 60 years and over taking regular weight bearing exercise and dietary calcium supplementation for two years. The ultradistal region of the forearm is predominantly composed of trabecular bone. No significant effect was shown in the lumbar spine, also trabecular bone, but this may reflect the poorer precision for these measurements and the large intersubject variation in our study sample. The distal site of the forearm is predominantly cortical bone, and the lack of response may reflect the lower turnover at this site.

The calcium group taking exercise experienced fewer falls than the calcium group. This finding supports the view that improving balance, strength, and flexibility through exercise might make falls less likely.3 This study provides a reminder that to focus on improving bone density is to address only part of the problem; prevention of falls might contribute substantially to reducing fracture rates. The association observed in this study between exercise and a reduced tendency to fall may be of considerable importance in fracture prevention and merits further study.