Watch for bone loss in adolescents who undergo bariatric surgery

Adolescents who undergo bariatric surgery lose bone in the first 2 years after surgery, but their bone mineral density (BMD) does not fall below average for their gender and age, according to a report published in Pediatrics.

Investigators from Cincinnati Children’s Hospital Medical Center, Ohio, did a retrospective chart review of 61 adolescents (mean age, 17.3 years) who underwent laparoscopic Roux-en Y gastric bypass between 2001 and 2008 and had dual-energy radiograph absorptiometry (DXA) scans before surgery (when possible) and then every 3 to 6 months for 2 years. Thirty-nine of the adolescents could not have DXA scans before surgery because excessive weight prevented use of the densitometer; these children had their initial scans within 6 months postoperatively.

Whole-body bone mineral content (BMC) and BMD declined significantly (P

Whole-body BMC decreased by 5.2% at the end of 1 year and by 7.4% by 2 years after bariatric surgery. Weight loss accounted for 14% of the loss in whole-body BMC in year 1 after surgery.

Although the BMD z scores decreased, they still remained above average for age throughout the 2 years of the study, likely because of the high BMC and BMD before surgery in this population. Researchers caution that these patients may still be at risk for fracture at a later time if their bone loss continues, so monitoring their BMD z scores past 2 years is prudent.

Potential mechanisms behind the bone loss are several. Weight loss itself may result in loss of bone mass. Absorption of nutrients may be altered with bariatric surgery, contributing to nutritional deficiencies. Postoperative changes in hormones may also contribute to bone loss.

Physicians should expect to encounter more such patients in the future because the number of patients younger than 20 years who underwent bariatric surgery to treat obesity more than tripled between 2000 and 2003.

Kaulfers AM, Bean JA, Inge TH, Dolan LM, Kalkwarf HJ. Bone loss in adolescents after bariatric surgery. Pediatrics. 2011. Epub ahead of print.