Teens Lose Bone Mass after Bariatric Surgery

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Obese teens lose bone mass during the first two years after bariatric surgery according to a retrospective case review published online in the journal Pediatrics.

The prevalence of overweight in pediatric age groups has nearly tripled in the last 30 years. It is estimated 16.1% of adolescents (12 to 19 years old) in the United States are overweight. Overweight adolescents are at an increased risk of becoming obese adults.

Bariatric surgery is becoming an acceptable way to treat obese teens with obesity-related comorbidities, including degenerative joint disease, hypertension, and type 2 diabetes.

Teen years are a time when young people should be reaching peak bone mass. Loss of bone mass could put future bone health at risk and lead to increased risk of osteoporosis as adults.

Anne-Marie D. Kaulfers, MD, of Cincinnati Children's Hospital Medical Center, and colleagues conducted a retrospective review of the medical records of 102 young patients who had laparoscopic Roux-en-Y gastric bypass surgery from 2001 to 2008. The final analysis included 61 patients, 51 of whom were female and whose age averaged 17. The primary reason for exclusion was a baseline weight that exceeded the limits of the densitometry machine.

To be considered for the surgery, the overweight teens had to meet five criteria: unsuccessful weight-loss attempts lasting more than six months, body mass index (BMI) >35, one or more obesity-related comorbidities, completion of all or most linear growth, and acceptable psychologic evaluation.

Patients underwent dual x-ray absorptiometry (DXA) before surgery and then every three to six months afterward for two years. For each patient, the researchers calculated whole-body bone mineral content and BMD z score.

The researchers found that 100% of the teens had a significant decrease in whole-body BMC, BMD z score, and weight over time after surgery (P

Bone mineral content decreased by 7.4% during the period reviewed. BMD z score decreased from 1.5 to 0.1.

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Preoperative BMI averaged 54 to 55, weight averaged 335 pounds among girls and 367 pounds in boys, and height averaged 65.9 inches in girls and 68.6 inches in boys. The predicted weight loss was 41.4 pounds at six months, 58.4 pounds at 12 months, 61 pounds at 18 months, and 49.2 pounds at 24 months.

On average the patients had three DXA scans during follow-up; all of the study participants had at least two scans. The last scan occurred an average of 13.9 months after surgery (range of 2.8 to 26.8 months).

The preoperative whole-body bone mineral content averaged 2,692 g, decreasing to 2,552 g after one year (5.2%) and to 2,494 g at two years (7.4%).

Weight and bone mineral content declined in a curvilinear manner over time (P

The patients' mean BMD z score decreased from 1.5 at baseline to 0.1 over the two-year follow-up period, BMD z score remained above average for the cohort.

In contrast to bone mineral content, BMD z score did not correlate significantly with weight change (P=0.73).

The researchers concluded “Bariatric surgery is associated with significant bone loss in adolescents. Although the predicted bone density was appropriate for age 2 years after surgery, longer follow-up is warranted to determine whether bone mass continues to change or stabilizes.”

However, the long-term consequences of the surgery in children and adolescents remain unclear. These adolescents need to be followed long-term to determine if the decrease in BMD z score continues and increases their risk for future fractures.

Sources
Kaulfers AD "Bone loss in adolescents after bariatric surgery" Pediatrics 2011; DOI:10.1542/peds.2010-0785.

Apovian CM “Best Practice Guidelines in Pediatric/Adolescent Weight Loss Surgery” Obesity Research (2005) 13, 274–282; doi: 10.1038/oby.2005.37

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