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Bariatric surgery showed association with bone loss at total hip, femoral neck
Calcium and vitamin D malabsorption reported after gastric bypass surgery.
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Obese individuals who underwent Roux-en-Y gastric bypass had decreased bone mineral density at the femoral neck and total hip at one year in a new study.
Researchers at Columbia University conducted a one-year prospective longitudinal study to assess BMD following Roux-en-Y gastric bypass in 23 obese individuals aged 20 to 64 years. The main outcome measures were serum parathyroid hormone, 25-hydroxyvitamin D, osteocalcin urinary N-telopeptide and BMD, using DEXA.
One year after the surgery, patients lost an average of 45 kg (P≤.01) and BMD decreased by 8% at the total hip and 9.2% at the femoral neck. The declines in BMD were strongly associated with the extent of weight loss, according to the researchers. They reported no changes in lumbar spine or distal radius BMD.
“Our research shows that deficiencies of calcium and vitamin D absorption occur following gastric bypass surgery. When analyzing hip bone density, we found that those who lost the most weight also lost the most bone,” Shonni J. Silverberg, MD, professor of medicine at Columbia University College of Physicians & Surgeons, said in a press release.
Increases in parathyroid hormone levels from 43 pg/mL to 50 pg/mL (P≤.001) and declines in urinary calcium from 161 mg per day to 92 mg per day (P≤.001) were reported as early as three months after the surgery. After one year, despite doubling calcium intake from 1,318 mg per day to 2,488 mg per day (P≤.001), and increasing vitamin D intake by 260% from 658 IU per day to 1,698 IU per day (P≤0.05), parathyroid hormone and serum 25-hydroxyvitamin D concentrations were unchanged from baseline levels. These findings are consistent with malabsorption of calcium and vitamin D, according to Silverberg.
“The calcium and vitamin D deficiencies may be due to the alterations in the gastrointestinal tract that take place during these procedures. These deficiencies may be restored if the amount of calcium and vitamin D supplementation is increased appropriately,” Silverberg said. – by Katie Kalvaitis
J Clin Endocrinol Metab. 2008;doi:10.1210/jc.2008-0481.
Bariatric surgery is bad for the skeleton; this has been well known for a long time. Nutritional health after bariatric surgery is absolutely critical. One concern with this study is the small number of subjects (n=23). The unanswered question is why the bone density is decreasing so markedly and so rapidly after surgery. There are a couple of things that come to mind. One possibility is that despite normal vitamin D levels the skeleton may not be mineralizing as quickly as it should and there may be some element of osteomalacia. The parathyroid hormone and vitamin D levels do not point to that but the levels of the markers of resorption and formation point in that direction. Another potential mechanism may be technical and related to the marked decrease in fat tissue between the two DEXA scans. If this were the major reason I would have expected to also see a decrease in bone density at the spine.
– Michael Kleerekoper, MD
Endocrine Today Editorial Board member
Although we have known for some time that bariatric surgery is associated with adverse effects on bone physiology, this study underscores the reality of this association and the need for not only further investigation but optimal management. After bariatric surgery, as a result of the weight loss there is an unloading phenomenon. The physiologic nature of bone loss has to do with an uncoupling between bone formation and bone resorption, where there are increases in bone resorption but no simultaneous increase in bone formation so there is a net loss of bone. Another reason for this bone loss may be due to vitamin D deficiency. Procedures like Roux-en-Y gastric bypass are thought to be associated with some element of malabsorption. Many patients actually have vitamin D deficiency going in to bariatric surgery and vitamin D deficiency itself is associated with secondary hyperparathyroidism, an independent risk factor for decreasing BMD and osteomalacia. However, it is unclear whether vitamin D deficiency is actually due to the malabsorptive procedure or not. The American Association of Clinical Endocrinologists has evidence-based clinical practice guidelines on nutritional and metabolic perioperative management of bariatric surgery with a section on bone and vitamin D.
– Jeffrey I. Mechanick, MD
Associate Clinical Professor of Medicine, Division of
Endocrinology, Diabetes and Bone Diseases
Director of Metabolic Support,
Mount Sinai School of Medicine