Dramatic declines in bone mass may occur after gastric bypass surgery, particularly among postmenopausal women, US research shows.
In findings that suggest the need for targeted bone health interventions after bariatric procedures, researchers from California showed that postmenopausal women had declines in spinal BMD averaging 12% in the year after undergoing Roux-en-Y gastric bypass.
The bone loss after marked weight loss in obese people could be missed or underestimated by conventional densitometry techniques such as DXA, as it was only revealed with quantitative computed tomography (QCT), the clinicians said in the Journal of Bone and Mineral Research.
The findings come from a one year follow up study of 48 obese adults who underwent Roux-en-Y gastric bypass, including 11 postmenopausal women and 10 men. The patients lost an average of 30% of preoperative weight (37kg) and showed detrimental effects on bone turnover, bone mass, porosity and strength within six months.
The detrimental effects persisted at 12 months, and included significant declines in femoral neck BMD of 8% and spinal BMD declines of 8%.
Declines in bone mass were greater for postmenopausal women, among whom spinal BMD declined by 11.6% at 12 months.
At the total hip, the percentage decline in BMD was larger for postmenopausal women than for premenopausal women or men (12.2% vs 7.2% and 6.8% respectively).
There were also significant detrimental changes in bone microarchitecture and strength, seen at both the radius and tibia.
The researchers said the detrimental changes in bone would likely persist beyond a year, based on findings from previous longer term studies of bone changes with bariatric surgery.
And they emphasised that postmenopausal women were particularly susceptible to the detrimental effects of bone loss on fracture risk because of their age and hormonal changes.
“Our results suggest … that the postmenopausal skeleton is more vulnerable to the dramatic increase in bone resorption that characterizes RYGB-induced loss of bone mass. Possibly, the heightened vulnerability is due to the postmenopausal woman’s distinct sex hormone milieu or lower muscle mass,” they noted.
They said it was already known that gastric bypass had negative effects on bone loss due to nutritional deficiencies from vitamin D and calcium malabsorption.
However the extent of the problem may have been masked by the use of DXA, which could be inaccurate after major weight loss due to changes in soft tissue around bone.
“Additional investigation should address strategies to avoid long-term skeletal consequences of this otherwise beneficial procedure, perhaps targeting postmenopausal women with screening and preventive or therapeutic interventions,” they suggested.. Interventions such as exercise, calcium, vitamin D, and protein supplementation had recently been shown to attenuate postoperative declines in BMD after bariatric surgery, they added.