Adolescent bone density decreases, rebounds after obesity surgery

Reuters Health Information: Adolescent bone density decreases, rebounds after obesity surgery

Adolescent bone density decreases, rebounds after obesity surgery

Last Updated: 2015-03-26

By Lorraine L. Janeczko

NEW YORK (Reuters Health) - After adolescents have gastric bypass surgery, their bone density decreases, but after two years it returns to within normal range, new research from Sweden suggests.

Adolescents' bodies and skeletons change significantly over the two years following laparoscopic Roux-en-Y gastric bypass (LRYGB) surgery and appear to be influenced to different degrees in males and females, with males losing more fat and preserving more lean mass than females, the authors reported in their poster March 5 at ENDO 2015, the annual meeting of the Endocrine Society, in San Diego, California.

Decreasing bone mineral density Z-score (BMD-Z) appears to bring most patients back in line with the non-obese population within two years, they wrote.

While the decrease in bone mass and increase in bone turnover after gastric bypass surgery has been described in adults, " o previous study has reported serum bone markers to assess bone turnover after bariatric surgery in the adolescent," the authors wrote.

"Studies in adults that have examined the effects of RYGB on bone health have shown significant changes bone turnover markers, a sign of increased bone remodeling," lead study author Dr. Eva Gronowitz, research coordinator in the Center for Pediatric Growth Research of the Sahlgrenska Academy at the University of Gothenburg, Sweden, told Reuters Health by email.

"So it's very important to follow young healthy individuals during childhood and adolescence, a time when much more bone is deposited than withdrawn and the skeleton grows in both size and density," she advised.

"Our study shows that we can maintain good bone health two years after bariatric surgery but that it is very important for patients to be compliant and follow their surgery with oral vitamin supplementation and DXA [dual-energy X-ray absorptiometry]," she added.

Dr. Gronowitz and her colleagues followed 50 female and 22 male morbidly obese adolescents, average age 16.5, undergoing LRYGB. Their mean body mass index (BMI) was 44.8 kg/m2 and they were.

Before their surgery and at one and two years post-operatively, the patients underwent DXA body composition and serum bone marker analysis.

Two years after surgery, their overall mean BMI decreased by 15.1 kg/m2. Their body composition changed, with a reduced percentage of fat mass (51.8% to 40.9%; p<0.0001) and an increased percentage of lean mass (47.0% to 56.8%; p<0.0001). Males lost more fat than females (-17.3% vs -9.5%; p<0.0001).

The mean baseline BMD-Z was 1.85 and decreased at two years to 0.52. Also at two years, four patients who began the study with a low baseline BMD-Z (-0.6 to -0.5) reached more than one standard deviation below the accepted mean for their age and gender.

Baseline bone markers showed greater bone turnover in males than females. After LRYGB, concentrations of serum markers of bone resorption (carboxy-terminal collagen crosslinks, p<0.0001) and synthesis (osteocalcin, p<0.0001; procollagen type 1 amino-terminal, p=0.003) rose in the first year and modestly declined in the second year, with absolute levels of these markers higher in males.

Regarding the data, Dr. Gronowitz wrote in an email, "Ongoing growth in males may interfere with the results, despite the male patients appearing preoperatively to have achieved near adult height. Another potential explanation could be that obese males are more active than obese females."

"We know from the literature that boys are skeletally more immature than girls in this age group, and examination of serum bone markers demonstrated greater bone activity in boys than in girls in this study," she added.

Senior author Dr. Jovanna Dahlgren, professor of pediatric endocrinology in the Department of Pediatrics at the Sahlgrenska Academy, told Reuters Health by email, "The results are not at all surprising, as this is also found in adults. Moreover, in the clinical setting, this will be the major issue to follow for the long term. We have cases of severe osteoporosis in adults and need to investigate the exact mechanisms behind the phenomenon."

As to future research, Dr. Gronowitz wrote that her research team has begun their five-year followup in the study participants using DXA, and they are also including a comparison group of obese adolescents who, five years ago, were treated with lifestyle changes instead of surgery. They hope to have updated results in about one year.

The authors reported no disclosures.


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