Older men with lower amounts of muscle mass have significantly increased risk of hip and potentially other fractures, new research led by investigators at Sutter Health’s San Francisco Coordinating Center (SFCC) in San Francisco, CA has shown.
Results of a prospective study were published online earlier this month in the Journal of Bone and Mineral Research, the official journal of the American Society for Bone and Mineral Research.
“Previous findings from our research and other studies have shown that low DXA lean mass—a commonly used but inaccurate approximation of muscle—is unrelated to a higher risk of fracture. This has led some researchers to erroneously conclude that muscle is relatively unimportant for fracture risk,” says Peggy Cawthon, Ph.D., lead author of the study, principal investigator of the Osteoporotic Fractures in Men (MrOS) Study Research Group at SFCC and a professor in the department of epidemiology and biostatistics at the University of California, San Francisco. “However, these new results suggest low muscle mass is in fact associated with increased risk of hip fractures in older men, even after accounting for factors such as age and bone mineral density that may influence muscle mass and fracture risk.”
Dr. Cawthon and colleagues at leading academic medical centers across the U.S. prospectively studied 1,363 men (mean age, 84.2 years). The risk of fracture by quartile of D3Cr muscle mass was determined, and the study authors also investigated the mediating influence of physical performance (walking speed, chair stands and grip strength) on the relationship between muscle mass and fracture.
Results showed D3Cr muscle mass weakly correlated with femoral BMD (r=0.10, p<.001). However, D3Cr muscle mass correlated strongly with fractures, especially hip fracture. Compared with men in the highest quartile, those in the lowest quartile of D3Cr muscle mass/weight were about twice as likely to have a clinical fracture, any non-spine fracture, and were about six times more likely to have a hip fracture after approximately four years of follow-up. Study authors believe the relationship between D3CR muscle mass and fracture may be mediated by poor physical performance.
D3Cr dilution assessment of muscle mass—currently available only in research settings and being tested by the MrOS Study and other researchers for clinical use—relies on several aspects of creatine biology to estimate muscle mass that do not rely on the same assumptions of compartment models (such as DXA), and may therefore represent a more accurate assessment of muscle mass.
“The clear association between muscle mass and hip fracture was striking. For example, men in the lowest quartile of muscle mass were almost six times more likely to have a fracture than men highest quartile,” says Steve Cummings, M.D., director of the SFCC and a principal investigator of MrOS at Sutter’s California Pacific Medical Center. “Our findings suggest muscle mass is an important contributor to fractures. Resistance exercise and even simple activities like climbing stairs may be important for maintaining muscle strength and preventing fractures, however more information from the best evidence –randomized controlled trials – is needed to confirm these findings and help guide clinical decision making.”
Dr. Cawthon notes that a limitation of the study is its sole cohort was male, as the measure of muscle mass was added to an ongoing study about osteoporosis in men (MrOS). “It is important to determine if these associations are also true in women,” she says. “If so, then it will be critical to test whether interventions that improve muscle mass also lower fracture risk, and how the D3Cr dilution assessment of muscle mass may potentially be used in the clinic to measure health outcomes.”
About 36 million falls are reported among older adults each year—resulting in more than 32,000 deaths. Every year, about three million older adults are treated in emergency departments for a fall injury. One out of every five falls causes an injury, such as broken bones or a head injury. Each year at least 300,000 older people are hospitalized for hip fractures.
This study was supported by the National Institutes of Health, with funding from the National Institute on Aging, the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Center for Advancing Translational Sciences.
Journal of Bone and Mineral Research