Bone Density Loss Seen After Bariatric Surgery in Teens

Although bariatric surgery is quite effective for weight loss in teens with obesity, it also may weaken the bones, according to a prospective longitudinal study.

Over the course of 1 year after undergoing sleeve gastrectomy, teens saw a 12 mg/cm³ drop in average vertebral bone mineral density (BMD), while nonsurgical controls saw no change (P<0.001), reported Miriam Bredella, MD, of Massachusetts General Hospital in Boston, and colleagues.

Sleeve gastrectomy patients also saw a 6 mg/cm³ reduction in cortical vertebral BMD versus a 4 mg/cm³ reduction in those who didn't opt for surgery (P=0.52), the group wrote in the Journal of Bone and Mineral Research.

Furthermore, sleeve patients had a significant 2.8% decrease in bending stiffness, while nonsurgical controls had a 2.5% increase in this measure.

While other measures, including body strength, thigh muscle area, visceral adipose tissue, and trabecular vertebral BMD initially looked like they significantly decreased for the surgical patients, these differences were no longer significant after adjustment for 12-month change in body mass index (BMI). Essentially, these reductions were all attributable to the drop in BMI that occurred after surgery.

"Weight loss surgery is very effective in treating obesity and obesity-associated comorbidities in adolescents and young adults with obesity; however, it can cause loss of bone density and strength," said Bredella in a statement.

"We hope that our study raises awareness of the importance of bone health after weight loss surgery, so physicians can make sure that children eat a healthy diet with enough calcium and vitamin D and engage in weight-bearing activity to build up muscle mass, which is good for bones," she added.

These findings don't necessarily come as a surprise, as many forms of bariatric surgery are associated with a reduction in nutrient absorption after removal of parts of the stomach. Postsurgical nutritional supplementation is therefore vital for patients.

However, to keep this in perspective, prior studies have also linked obesity with a higher risk for weaker bones.

Bredella's group explained that all sleeve patients were provided with both calcium and vitamin D supplementation based on 25OHD levels: those with 25OHD levels of 20 to 30 ng/mL received 4,000 IU/day; those with levels of 12 to 20 ng/mL received 50,000 IU/week for 2 months; and those with levels under 12 ng/mL took 50,000 IU/week for 3 months.

There were no significant drops in calcium, phosphorus, and vitamin D and no increases in parathyroid hormone levels after surgery. "This suggests that the BMI-independent reductions in bending strength and cortical BMD reflect alterations other than mechanical unloading or insufficient calcium or vitamin D intake," Bredella and team wrote.

The prospective study compared 29 patients who underwent sleeve gastrectomy with 30 nonsurgical controls. All participants had to be 13 to 25 years old and have moderate-to-severe obesity (BMI of ≥35) with at least one comorbidity or a BMI of ≥40. None of the adolescents could weigh over 441 lb due to weight limitations of the CT and MRI scanners.

The vast majority were female; average baseline BMI in sleeve patients was 47.4 and weight was 294.1 lb. About 45% of sleeve patients were white, 28% were Hispanic, and 17% were Black.

During the year-long follow-up, sleeve patients lost an average of 75.6 lb, while nonsurgical controls had no significant weight change. Sleeve patients also saw a 12.3-point drop in BMI.

"A longer follow-up period is necessary to determine whether the deleterious changes in vertebral strength will continue and lead to spine fractures," the group concluded.

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