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Bone loss, bone strength deterioration observed after RYGB
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Despite weight stabilization and an improvement in metabolic parameters, patients undergoing Roux-en-Y gastric bypass surgery experienced bone loss and a decline in bone material strength that persisted 2 years after surgery, according to findings from a Danish study.
“In contrast to our hypothesis, the findings from this study indicate a persistent decline in [bone mineral density] and a progressive deterioration in bone microarchitecture and estimated strength at both weight bearing and nonweight-bearing skeletal sites in the second year after Roux-en-Y gastric bypass,” Vikram V. Shanbhogue, MD, of the department of endocrinology at Odense University Hospital, and colleagues wrote. “This continued and excessive bone loss persisted despite attainment of steady-state in weight, fat and lean body mass, adipokines, such as leptin, and gut hormones, such as insulin, 1 year after surgery.”
Shanbhogue and colleagues analyzed data from 23 adults with BMI at least 35 kg/m² with at least one obesity-related complication, or BMI at least 50 kg/m², who were eligible for Roux-en-Y gastric bypass (RYGB) surgery; patients were recruited from Odense University Hospital and Hospital of Southwest Denmark between October 2011 and August 2012 (six with type 2 diabetes; one with type 1 diabetes). Areal BMD was measured at the total hip and lumbar spine via DXA at baseline and 1 and 2 years; whole-body DXA was used to measure total fat and lean body mass. Bone geometry, volumetric BMD and microarchitecture of the distal radius and tibia were measured via high-resolution peripheral quantitative (HR-pQCT) at baseline and 1 and 2 years. Patients provided fasting blood samples at each visit for measurements of parathyroid hormone, 25-hydroxyvitamin D, follicle-stimulating hormone, adiponectin and leptin, as well as bone turnover markers, including procollagen type 1 N-terminal propeptide (P1NP) and C-terminal telopeptide of type 1 collagen (CTX).
From baseline to 12 months, median weight loss was 32 kg (24.1%; P < .001); median body weight did not change between months 12 and 24 (P = .5).
In assessing DXA measurements, researchers observed a decrease in mean total hip areal BMD at 12 months (–8.2%; P < .001) and 24 months (–10.5%; P < .001), as well as a decrease in mean spine areal BMD at 12 months only (–3.5%; P < .001).
In assessing HR-pQCT, researchers found that bone geometry, volumetric BMD and bone microarchitecture and estimated bone strength all deteriorated throughout the study period. Within the cohort, total volumetric BMD at the radius declined by a mean 4.3% from baseline to 24 months (P < .001), as did cortical thickness (–2.9%; P < .01); cortical porosity increased by 21% (P < .05). The estimated failure load declined by 5.2% during the study period (P < .01).
At the tibia, total volumetric BMD declined by a mean 7.2% throughout the study period (P < .001), leading to an estimated failure load decline of 7% in the 2 years after gastric bypass (P < .001).
“These results lend credence to the notion that adaptation of bone is a slow, ongoing process that continues after stabilization of metabolic parameters and body weight, such that attainment of skeletal equilibrium lags metabolic equilibrium,” the researchers wrote. – by Regina Schaffer
Disclosure: The Municipality Region of Southern Denmark supported this study. The researchers report no relevant financial disclosures.
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