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MrOS study: Mortality risk influences fracture prediction in older men with weight loss
Older men who experience moderate weight loss are more like to experience a central body fracture vs. men who maintain a stable weight, but ignoring morality risk may lead to an overestimation of long-term absolute fracture probability, according to an analysis of the Osteoporotic Fractures in Men, or MrOS, study.
“Previous studies examining the association of weight loss with fracture outcomes in older adults have utilized traditional Cox proportional hazards regression models to analyze the association of weight change with fracture,” Kristine E. Ensrud, MD, MPH, of the University of Minnesota School of Public Health, and colleagues wrote. “These approaches treat mortality as an uninformative censoring event and assume that subjects censored due to death are representative of those still at risk of fracture at that point in time and have the same distribution of time-to-fracture as subjects who experience fracture. However, ignoring mortality may not provide accurate estimates of risk of fracture because weight loss in older adults strongly predicts death, making mortality a competing risk.”
Ensrud and colleagues analyzed data from 4,523 men who completed baseline and follow-up examinations in the prospective MrOS study (mean age, 78 years). Body weight was measured at both visits; weight change was categorized as moderate weight loss ( 10%), mild weight loss (5%-10%), stable weight (< 5% loss or gain) or weight gain ( 5%). Participants completed questionnaires and interviews at the second examination to assess medical conditions, intention to lose weight and falls in the past year. Researchers contacted participants every 4 months after the follow-up visit (serving as baseline for this study) to ask about fractures; self-reported events were confirmed by radiographic reports. Deaths were verified with death certificates. Researchers estimated the absolute probability of a central body fracture by weight change category using the Kaplan-Meier method and cumulative incidence function accounting for competing mortality risk, and used Cox proportional hazard regression and subdistribution hazards analysis, with death as a competing risk, to determine the risk for a central body fracture by weight change category.
Mean follow-up time after second examination was 7.9 years for central body fracture and 8.1 years for mortality.
Between baseline and second visit, participants experienced a mean 1.6% decrease in body weight; 283 (6.3%) men had moderate weight loss; 742 (16.4%) had mild weight loss; 3,076 (68%) had stable weight; and 422 (9.3%) experienced weight gain.
During follow-up after the second examination, 337 men (7.5%) experienced a central body fracture; 1,569 (34.7%) died before experiencing a central body fracture. Both men who died and men who experienced a central body fracture experienced a similar change in body weight (–2.5% and –2.3%, respectively), but men who survived without fracture experienced a smaller weight change (–1%), according to researchers.
When comparing men with moderate weight loss and mild weight loss, researchers found that the competing risk approach compared with traditional survival analysis resulted in a lower estimate of absolute fracture probability, with the difference growing as follow-up time increased. Using traditional Kaplan-Meier survival analysis, the absolute probability of a central body fracture among men with moderate weight loss was 6.8% (95% CI, 4-10.6) at 5 years and 16.9% (95% CI, 10.5-24.7) at 10 years; using a competing risk approach, this fell to 5.7% (95% CI, 3.4-8.8) at 5 years and 10.2% (95% CI, 6.8-14.4) at 10 years.
Compared with men of stable weight, men with moderate weight loss had a 1.7-fold higher age-adjusted risk for central body fracture (HR = 1.73; 95% CI, 1.16-2.59), according to Cox regression analyses. However, in subdistribution models, the age-adjusted risk for central body fracture among men with moderate weight loss was attenuated by 27%, according to researchers.
“Older men with weight loss late in life who survive have a higher risk of central body fractures, including hip fractures,” the researchers wrote. “However, not taking into account the competing mortality risk among men with weight loss greatly overestimates their long-term absolute fracture probability and adjusted facture risk. These findings suggest that among older men with a history of weight loss in old age, a competing risk approach is needed to better inform fracture risk assessment and clinical decision making.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.