Gastric bypass surgery during adolescence was associated with significant bone loss in 61 patients in a retrospective study, but participants’ predicted bone density at 2 years following the procedure did not fall below the expected value for gender and age.
Whole body bone mineral content, bone mineral density z score, and weight each decreased significantly over time in the 61 patients, all of whom underwent Roux-en Y gastric bypass at Cincinnati Children’s Hospital during 2001-2008. Predicted bone mineral content decreased by 7.4% (from 2,692 g to 2,494 g) in the first 2 years after surgery, and the predicted age- and gender-specific bone mineral density z score decreased from 1.5 to 0.1, Dr. Anne-Marie D. Kaulfers and her colleagues from Cincinnati Children’s Hospital Medical Center reported online in the March 28 issue of Pediatrics.
However, the z score remained above average for age and gender throughout the 2-year follow-up period, they said (Pediatrics 2011 March 28 [doi:10.1542/peds.2010-0785]).
In the first year following surgery, reductions in weight correlated significantly with reductions in bone mineral content, and weight loss was shown to account for only 14% of the decrease in bone mineral content, they noted.
Concern about possible bone loss among adolescents undergoing gastric bypass surgery is particularly relevant given that more than 18% of adolescents in the United States are obese and that the number of adolescents who elect to undergo gastric bypass surgery continues to rise; from 2000 to 2003 the number increased threefold from 222 to 771, the investigator said.
Furthermore, adolescents who undergo Roux-en Y gastric bypass tend to experience dramatic weight loss of up to 73% of their excess weight by 1 year, and in adult studies, the extent of bone loss has been shown to be related to the amount of weight loss.
"Loss of bone mineral at the age when adolescents should be approaching peak bone mass (estimated at age 20) could potentially compromise their future bone health," the investigators noted.
Though limited by sample size, retrospective study design, and relatively short follow-up, among other factors, the findings of this study, which included teens with an average age of 17.3 years, a body mass index of greater than 35 (mean of 54.4), and at least 1 obesity-related comorbid illness, showed that bone loss did not fall below expected values at 2 years following surgery. It is likely that this finding is a consequence of high bone mineral content and density prior to surgery in this extremely obese population, the investigators said.
If bone loss continues in this population, however, the risk of fractures later in life might be increased.
"These adolescents need to be followed over the long-term to determine if the decrease in BMD z score continues and increases their risk for future fractures," they said, adding that the effects of bariatric surgery on bone mass and the clinical consequences of this need to be better understood.
This is especially important for primary care physicians who will be providing routine care for these patients.
The primary care physician should be aware of the possibility of low bone mass in adolescents after bariatric surgery so that it can be monitored and managed appropriately, they concluded.
The authors reported having no relevant financial disclosures. This study was funded by the National Institutes of Health.