The notion that high BMI is protective against fracture is widely held among researchers and clinicians, but a retrospective study out of Rush University Medical Center offers a more nuanced view, finding that sleeve gastrectomy bariatric surgery significantly reduces the risk of sustaining a fracture in individuals with severe obesity.
Over the years, researchers have found evidence that obesity may help safeguard against osteoporosis by boosting bone density, according to Alfonso Torquati, MD, MSCI, Helen Shedd Keith Professor and Chair of the Department of Surgery at Rush University Medical Center. That has led some to conclude that losing weight could result in a harmful reduction in bone density, thereby increasing fracture risk. In 2017, for example, the multicenter, randomized Look AHEAD clinical trial found that overweight or obese individuals with diabetes who lost an average of 6% of body weight by following a program of intensive lifestyle intervention had a 39% higher risk of frailty fracture than overweight or obese individuals who participated in diabetes support and education and lost an average of 3.5% of body weight.
“Excess body weight increases the load on the skeleton, and the high levels of leptin seen in obesity provide stimulation of bone formation,” Dr. Torquati says. “This results in higher levels of bone density. However, the protective effect of high bone density on fracture risk is controversial and very difficult to prove. More straightforward is to speculate that the benefit of sustained and significant weight loss can lead to less risk of fall-related injuries that are the ultimate cause for traumatic bone fracture.”
Intrigued by a spate of studies suggesting that bariatric surgery could contribute to bone density changes, Dr. Torquati and colleagues set out to investigate the longitudinal effect of surgical weight loss on real risk of fracture.
“Our initial hypothesis was that, in bariatric surgery patients receiving adequate calcium and vitamin D supplementation, the risk of bone fracture was going to be similar to that observed in a matched population that did not undergo surgery,” Dr. Torquati says. “Our study’s hypothesis was confirmed by the results, including an expected lower odds of fracture in patients undergoing sleeve gastrectomy.”
Sleeve Gastrectomy Superior to Gastric Bypass at Fracture Risk Reduction
Using Medicare records from 2004 to 2014, Torquati and colleagues separated 49,113 bariatric surgery-eligible patients into three groups of 16,371 individuals each: a group of patients who did not undergo bariatric surgery, a group of patients who had undergone Roux-en-Y gastric bypass and a group of patients who had undergone sleeve gastrectomy. Over a three-year period, fracture rates between the individuals who did not have bariatric surgery and those who underwent gastric bypass were comparable, but people who underwent sleeve gastrectomy had much lower rates of fracture.
For individuals in the nonsurgical and gastric bypass cohorts, the overall likelihood of experiencing a fracture was similar, as were the odds of fracture of the humerus, radius or ulna, pelvis, or vertebrae. Patients who underwent sleeve gastrectomy had a lower risk of fracture in all categories compared with individuals who did not have surgery, and a lower risk of total fracture and humeral fracture compared with patients who underwent gastric bypass. The sleeve gastrectomy and gastric bypass groups had similar odds of radius or ulna, hip, pelvis, or vertebrae fracture. The study was published in JAMA Network Open earlier this year.
Gastric bypass effects weight loss, in part, by changing how the body absorbs nutrients, which can elevate fracture risk and may play a role in the development of metabolic bone disease, according to the researchers. After more than a decade of studying the relationship between metabolic bone disease and gastric bypass, Dr. Torquati believes a dearth of a key vitamin and mineral may explain why gastric bypass patients may be more susceptible to fracture.
“In the early years of bariatric surgery expansion, we saw many patients developing changes in the bone metabolism that potentially increase their risk of fractures,” Dr. Torquati says. “At that time, this was secondary to inadequate supplementation with vitamin D and calcium. In the last 10 years, all the patients undergoing bariatric surgery are receiving supplemental doses of vitamin D and calcium, and we very rarely see detrimental changes in the bone metabolism.”
Reassessing Obesity’s Benefits for Bones
This study may prompt a reevaluation of obesity’s role in protecting against osteoporosis.
“The generally accepted notion that obesity is protective when considering the risks of fracture may not be as straightforward as previously thought,” the researchers wrote. “The relationship between BMI, body composition and bone density may play an important role when evaluating the risk of fracture in patients with obesity.”
Dr. Torquati says the study should provide peace of mind to patients who may be considering bariatric surgery but worry about bone health.
“Our results showed that bariatric surgery may be associated with lower odds of fracture in the general population of patients with obesity,” he says. “Therefore, patients who are concerned about worsening osteoporosis after bariatric surgery should be reassured knowing this will not result in an increased risk of postoperative fractures, especially in patients undergoing sleeve gastrectomy.”