Is Bone Loss in Adolescents Following Bariatric Surgery Related to Weight Loss?
The study question: To what extent is the bone loss that teenagers experience following Roux-en-Y gastric bypass surgery related to weight loss?
This study used a retrospective case review of the charts of 61 adolescent patients who all received the same gastric bypass surgery. Whole-body bone mineral content and density were measured using dual-energy radiograph absorptiometry (DEXA). Where possible, scores for these measures were taken prior to surgery and every three to six months following surgery, for a two year period. Scores for the measures were standardized to make them comparable. Data analysis was adjusted to take age, gender and height into account. All patients were told to take a multivitamin with 1000 mg of calcium and 800 IU of Vitamin D daily following their surgery.
The results: Patients’ weight, whole-body bone mineral content and bone mineral density decreased significantly over time following surgery, with boys losing more weight than girls. Weight loss was greatest during the first year after surgery, and then stabilized. Whole-body bone mineral content decreased by 7.4% over two years following surgery. Bone density scores at two years, however, were within the expected values for patients’ age and gender. Weight loss was significantly correlated with the bone loss, but accounted for only 14% of the decrease in bone mineral content in the first year after surgery.
The study raises a number of questions. While there are potential mechanisms to explain just how bone loss could occur after bariatric surgery, these metabolic and hormonal mechanisms need to be investigated in more detail. No one has studied the long-term consequences of weight loss surgery on bone health, so we don’t know whether adolescents who have weight loss surgery could have an increased risk of bone fractures as they age, or not.
Is this study relevant to me? Yes, if you are a teenager or parent of a teenager who has had or is considering weight loss surgery. While the results regarding bone density scores are somewhat reassuring, teenagers may be at a higher risk for nutritional deficiencies because they may be less compliant about dietary recommendations and taking supplements.
Limitations of the study: The study only included the charts of 61 patients out of the 102 that were eligible. Some patients were excluded because they exceeded the weight limit of the machine used to measure bone density, so those with extreme morbid obesity were not included. This may bias the study results. Not all of the study measures were taken at the same time, which can introduce error. Weight loss can also thicken tissue around bone, resulting in overestimates of bone density, and consequently underestimating the true amount of bone loss. There is also no way to know from studying the patients’ charts retrospectively whether they took the daily multivitamin as instructed.
Find this study in PubMed:
Kaulfers AM, Bean JA, Inge TH, Dolan LM, Kalkwarf HJ. Bone loss in adolescents after bariatric surgery. Pediatrics. 2011 Apr;127(4):e956-61. Epub 2011 Mar 28.