Walking and Leisure-Time Activity and Risk of Hip Fracture in Postmenopausal Women
Walking and Leisure-Time Activity and Risk of Hip Fracture in Postmenopausal Women
Abstract & Commentary
Synopsis: Moderate levels of activity, including walking, are associated with substantially lower risks of hip fracture in postmenopausal women.
Source: Feskanich D, et al. Walking and leisure-time activity and risk of hip fracture in postmenopausal women. JAMA. 2002;288:2300-2306.
The aim of this study was to determine how much protection from hip fracture exercise confers. The study population was the Nurses’ Health Study, which is an ongoing cohort of 121,700 women who were nurses between the ages of 30 and 55 years at the time of enrollment in 1976. Approximately 98% of the participants are white. Data from 61,200 subjects were used in the present analysis. During the median length of follow-up of 11.6 years, there were 415 cases of hip fracture. The median age of fracture was 67 years. Physical activity was estimated by means of a questionnaire. Each activity was assigned a metabolic equivalent. One MET is the energy expenditure from sitting quietly.
The group was relatively sedentary, with a median of 7 MET h/wk (2.3 h/wk of walking at an average pace). Nineteen percent reported no activity. Active women had a lower BMI, were less likely to smoke, and were more likely to take hormones and calcium supplements. Both activity and body mass index (BMI) were inversely associated with risk of hip fracture. Women in the highest category of activity (MET > 24) had a relative risk of hip fracture of 0.45 (confidence interval, 0.32-0.63) and there was a dose-related reduction in risk. Women with a BMI < 23 had a significantly higher risk of hip fracture regardless of activity and those with a BMI > 30 had a significantly lower risk. The association between activity and hip fractures was dissimilar in hormone users and nonusers, such that hormone use protected most from hip fracture in those users who were sedentary. In those with the highest level of activity, hormone use added very little to the reduction in risk of hip fracture.
Comment by Sarah L. Berga, MD
What intrigued me most about this otherwise straightforward report was the finding that, at the highest levels of activity, hormone use offered little additional benefit over exercise alone in protecting from hip fracture. Estrogen was most effective in safeguarding the hip in sedentary women. This same relationship also held for calcium intake and activity. However, a high BMI did confer some additional protection from hip fracture even at the highest activity levels. This is important information to share with patients who are looking for nonhormonal strategies for managing menopause and aging.
The study has some important limitations, however, and patients must be cautioned about these as well. The mechanisms by which exercise or activity protect someone from hip fracture were not studied. Other studies have shown that activity correlates with bone density, but exercise also reduces falling, a major cause of hip fracture, by improving balance and muscle strength. Other types of fractures, including vertebral crush fractures, were not included in this analysis. Exercise and activity are less likely to strengthen vertebral bodies, and vertebral crush fractures are not typically attributable to falls. Given these considerations, it is premature to conclude that exercise is a good substitute for estrogen or other agents intended to reduce the risks of developing the clinical manifestations of osteoporosis. Also, it is not clear what role exercise or activity have in the treatment of established osteoporosis. Most importantly, as Feskanich and colleagues carefully point out, for exercise to safeguard against hip fracture, it must be ongoing. Women who decreased their activity levels during the follow-up period had an increased incidence of hip fracture. It is not uncommon for my patients to tell me that they are not worried about osteoporosis because they led an active life when they were younger. Apparently, this is not enough.
Another reason I chose to review this article is that doctors and patients alike are wondering what to do in the wake of the WHI. It has been suggested that alternative strategies other than HRT should be the mainstay for the prevention and treatment of osteoporosis. While there are many agents available, none of them are risk-free. For instance, the long-term effect of bisphosphonates has not been chronicled because not enough women have used them long enough to know. Some have suggested that hormones are better because they build bone of normal architecture, whereas this cannot be said for bisphosphonates. There is some concern that bisphosphonates may confer bone fragility after extended use or as bones age (because the bisphosphonates are incorporated into the bone matrix). Further, now that parathyroid hormone (PTH) is about to become available, we will have to figure out where it fits in the schemata for the prevention and treatment of osteoporosis.
Dr. Berga is Professor and Director, Division of Reproductive Endocrinology and Infertility, University of Pittsburgh.
Moderate levels of activity, including walking, are associated with substantially lower risks of hip fracture in postmenopausal women.Subscribe Now for Access
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