Loss of Total Body Lean Mass Linked to Increase Risk of Fractures

September 7, 2020

Patients attempting to lose weight through dietary changes should be advised of the importance of maintaining their existing muscle mass and strength through exercise, so as not to increase their risk of fractures, Canadian researchers say.

Patients attempting to lose weight through dietary changes should be advised of the importance of maintaining their existing muscle mass and strength through exercise, so as not to increase their risk of fractures, Canadian researchers say.

The researchers found that loss of total body lean mass, but not fat mass, is associated with increased fracture risk, particularly of the hip, independent of other risk factors.

“This is in line with a large amount of evidence implicating lean tissue (which partially reflects muscle mass) as more important than fat when it comes to skeletal health,” said Dr Bill Leslie, professor of medicine and radiology at the University of Manitoba.

“Rheumatologists should counsel patients attempting to lose weight that they need to look beyond the bathroom scale.It is vitally important to make deliberate changes in their diet and exercise that maintain muscle mass and strength.”

And clinicians should be aware that many clinical guidelines and fracture assessment tools, including FRAX, used to determine the need for osteoporosis therapy rely on measures of height and/or weight and do not take account of body composition, he adds, which means they may underestimate risk, particularly of hipfracture, in some patients.

“Weight and weight loss are crude measures and fail to distinguish the very different effects of muscle and fat on skeletal health,” he said.

The study included 9622 men and women aged at least 40 years, who had undergone two DXA scans of the lumbar spine and hip at least one year apart, identified from the database of the Manitoba bone mineral density testing programme. The median age of the patients was 67 year, the initial DXA assessment took place between May 2004 and February 2015, and the median interval between assessments was 3.3 years.

The researchers used information from the scans along with measurement of the patients’ weight and their sex to estimate their total body lean mass and total body fat mass loss at the two time points.

Linked population-based health service data showed that after the scan and during a mean follow up period of 6 years 692 patients experienced a major osteoporotic fracture and 194 a hip fracture.

Cox multivariable regression analyses were performed to assess the independent effects of prior total body lean mass and total body fat mass loss risk on fractures. Each additional standard deviation decrease in total body lean mass was associated with a 10-12% increased risk for incident major osteoporotic fracture of 10–12% and a 29–38% greater risk for incident hip fracture, when adjusted for loss of total body fat mass and other fracture risk factors. Total body fat mass was not found to be an independent risk factor for incident major osteoporotic or hip fracture

Change in body composition, and more specifically a loss of total body lean mass, is associated with increased risk of major osteoporotic and hip fracture, while loss in total body fat mass is not associated with increased risk of fracture, the researchers concluded, highlighting the importance of maintaining healthy bodyweight, composition, and muscle mass to reduce fracture risk.

They added that their results suggest that FRAX may underestimate fracture risk, particularly hip fracture risk, in patients losing total body lean mass, because the tool does not take account of body composition.

“Fracture risk assessment tools like FRAX consider weight but not weight loss or change in body composition which, as we've shown, is an additional consideration.Hip fractures are particularly sensitive to lean tissue loss, possibly due to falls which we could not directly assess in our study,” Leslie said. “Ongoing efforts to include falls in these risk scores may capture some of the impact of ‘muscle failure’ (sarcopenia) on fracture risk.”

He added that further research on the relative importance of muscle mass versus muscle function and their effects on falls and fracture risk is needed.

“Meanwhile, a bedside assessment of someone's nutritional status, muscle status and risk for falls are essential components of skeletal health assessment,” Leslie emphasised, and patients advised that “intentional weight loss should be accompanied by efforts to maintain muscle mass and strength, usually through a combination of diet and exercise.”

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REFERENCE

Leslie WD, Schousboe JT, Morin SN, et al. Loss in DXA-estimated total body lean mass but not fat mass predicts incident major osteoporotic fracture and hip fracture independently from FRAX: a registry-based cohort study. Arch Osteoporos. 2020;15(1):96. Published 2020 Jun 25. doi:10.1007/s11657-020-00773-w