BMD Loss Sustained for Years After Gastric Bypass

By | September 18, 2017

Bone density measurements show up to 15% mean decline in 5 years
by Nancy Walsh, Senior Staff Writer, MedPage Today September 13, 2017

Action Points
• Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
• Note that this observational study of 21 women who underwent Roux-en-Y gastric bypass revealed that post-procedure bone loss persists for at least 5 years.
• Despite that, only one of the 21 patients developed t-scores in the osteoporotic range.

DENVER — An unintended consequence of gastric bypass surgery — loss of bone mineral density (BMD) — persisted through 5 years of follow-up, a prospective study found.
Previous studies have shown that acute bone loss occurs in the first 1 to 2 years after Roux-en-Y bypass surgery, with one report by Elaine W. Yu, MD, and colleagues from Massachusetts General Hospital in Boston demonstrating that 2 years after surgery, bone mineral density (BMD) was 5% to 7% lower at the spine and 6% to 10% lower at the hip.
“There has been an increase in the utilization of gastric bypass procedures over the past 10 to 15 years, including in adolescents and older adults. This has implications for bone health, as these two populations may be uniquely susceptible to the negative skeletal effects of bariatric surgery,” Yu said.
However, little is known about the long-term trajectory of bone loss after gastric bypass, so she has continued to follow her cohort, presenting the 5-year follow-up at the annual meeting of the American Society for Bone and Mineral Research here.
The study included 21 patients whose body mass index (BMI) averaged 45 at pre-surgery baseline. Most were women, and mean age was 51. Baseline serum calcium and vitamin D were within the normal range. By the 5-year time point, average weight loss was an impressive 73 lb, she reported.
Bone health was assessed using multiple modalities. Areal BMD was measured by dual-energy x-ray absorptiometry (DXA) at the lumbar spine, total hip, and radius; vertebral trabecular volumetric BMD was measured at L1-L2 with quantitative computed tomography (QCT); and high-resolution peripheral QCT was used to assess the bone microarchitecture at the tibia and distal radius.
“There was significant bone loss in the 5 years after bypass surgery, with cumulative declines of 8% at the spine and approximately 15% at the hip as assessed by DXA,” Yu said. However, those losses in years 2 to 5 appeared to be less than what was initially seen in the first 2 years. During the first 2 years, the decreases at the spine and hip had been 6% and 12%.
Despite the large cumulative loss, only one patient had T-scores that fell to the osteoporotic range at 5 years, she noted.
At peripheral sites, there was a steady decline throughout the 5 years, with declines in total, trabecular, and cortical volumetric BND after year 2 being significantly greater. For instance, the changes in total volumetric BMD on high resolution peripheral QCT were -7.4% at the radius and -7.7% at the tibia, reaching -18.7% and -14.3 at the two sites, by 5 years.
The decline in cortical thickness also continued at 5 years, with a near doubling of cortical porosity over 5 years at the tibia and radius. There also was a deterioration of the trabecular compartment, although changes were not seen on high resolution peripheral QCT at the radius or tibia.
Further microfine element analysis of cumulative changes and densitometric microarchitectural parameters translated into declines in the estimated failure load at the radius of 20% and the tibia of 14%, with decreases continuing during years 2 to 5 being at the same rate as in the initial 2 years.
Serum collagen type 1 cross-linked C-telopeptide, a marker of bone resorption, also remained significantly elevated at 5 years compared with baseline, at about 150% of baseline value.
Yu and colleagues also looked at potential correlations between change in skeletal outcomes and potential explanatory factors, and found no relation between bone density and changes in lean mass or parathyroid hormone (PTH), but there was a correlation between the increase in cortical porosity and an increase in PTH at 5 years at the radius and tibia.
This correlation had not been detected before 5 years, and may have been influenced by the presence of outliers. “However, if this correlation can be replicated in other cohorts, it is possible that late increases in PTH may be contributing to increased cortical porosity 5 years after bypass,” she said.
The bone loss observed over 5 years did not correlate with weight loss or changes in lean mass, which suggests that mechanisms other than skeletal unloading may potentially contribute to the bone loss, she noted.
“We recommend that skeletal health be assessed and actively managed in patients who are undergoing Roux-en-Y gastric bypass,” she concluded.

Yu reported no financial conflicts.
• Reviewed by F. Perry Wilson, MD, MSCE Assistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner
• Primary Source
American Society for Bone and Mineral Research
Source Reference: Yu E, et al “Longitudinal 5-year changes in bone density and microarchitecture after Roux-en-Y gastric bypass” ASBMR 2017; abstract 1125.

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