Many adults who have gastric bypass surgery suffer bone loss in the years after their operation, and a new study shows the same thing happens to adolescents. It is a potentially-worrisome price to pay for fighting obesity.
Researchers led by Dr. Anne-Marie Kaulfers, then a clinical fellow in endocrinology at Cincinnati Children's Hospital Medical Center, looked at 61 adolescents who had Roux-en-Y gastric bypasses. A Roux-en-Y bypass involves making a small pouch from stomach tissue attaching it directly to the small intestine, bypassing most of the stomach and the first part of the small intestine, called the duodenum.
They found teens suffered 5.2 percent bone loss a year after surgery, which increased to 7.4 percent after two years. Obese teens already have an above-average amount of mineral mass in their bones, so even though they lost more than 7 percent of that mass, it decreased to the same amount that normal-weight teenagers have.
The study stopped two years post-surgery, and the researchers don't know whether the decline will continue beyond that.
"However, if bone loss continues, even at a slow rate, these patients may have an increased risk of fractures later in life," the authors wrote.
While some specialists say the findings aren't new because other studies showed similar results in adults, others say the study draws attention to one of the big risks of gastric bypass surgery.
"This study is very important because we all know that there are consequences to rapid weight loss, and bone loss has been a concern in adults and now we know that it happens in adolescents," said Dr. James Geiger, surgical director of the C.S. Mott Children's Hospital Comprehensive Weight Management Program in Ann Arbor, Mich.
Experts say it's important to learn more about bone loss in younger people who have a gastric bypass in order to determine why it happens, what the long-term consequences are and how possibly to reverse bone loss.
There are a couple of theories about exactly what causes post-operative bone loss.
"One is that as you decrease the amount of gut available to absorb nutrients, you decrease absorption of nutrients you need to develop bone mass, like vitamin D and calcium," said Dr. Jill Simmons, assistant professor of pediatrics at Vanderbilt University School of Medicine. "It's likely a combination of decreased nutritional absorption and a decrease in the amount of hormones that regulate bone mass, such as insulin-like growth factor 1 or IGF-1," she said.
Another theory is that overweight people have higher amounts of bone mass because their bones have to carry more weight.
"Obesity doesn't help any organ system except one -- the bones. It makes the bones stronger," said Dr. Nestor de la Cruz-Munoz, chief of the Division of Laparoendoscopic and Bariatric Surgery at the University of Miami School of Medicine.
Kaulfers, now an assistant professor of pediatrics at the University of South Alabama in Mobile, said that eating less food means getting fewer minerals, which could also lead to bone loss.
With so little data available, in part because bypass surgery on teens is fairly new and not performed in many places, experts say patients who fit the bill need to be followed over the long term.