SAN FRANCISCO – Bariatric surgery can be beneficial for obese people, but it also can lead to significant bone loss.
The limited data so far suggest that decreased bone mineral density after bariatric surgery is a real problem that increases the risk for fracture, Dr. Anne Schafer said at a meeting on osteoporosis sponsored by the University of California, San Francisco.
The extent of bone loss within a year after the most common bariatric surgery, Roux-en-Y gastric bypass, can be equivalent to "what you would expect in the first 5 years of menopause" in some women, said Dr. Schafer of the division of endocrinology at the University of California, San Francisco.
A 2011 study not yet published by the Mayo Clinic, Rochester, Minn., compared fracture rates in 277 patients undergoing bariatric surgery with local age- and sex-matched fracture rates. The surgeries occurred in 1985-2004, and 94% were gastric bypasses. The retrospective chart study found 138 fractures in 82 patients since the surgery, with a standardized incidence ratio of 2.1 for any fracture and 1.9 for fractures of the hip, spine, wrist, or arm after bariatric surgery, she said.
Dr. Schafer incorporated her own clinical experience with recommendations from the Endocrine Society and from Tufts University in advising clinicians to take the following steps in managing patients undergoing bariatric surgery.
Prior to surgery, check serum 25-hydroxyvitamin D (25[OH]D) levels and prescribe preoperative treatment to augment vitamin D in patients with low levels.
After surgery, all patients should take two multivitamins per day to make sure their micronutrient needs are met.
After malabsorptive bariatric surgery, such as gastric bypass, patients also should take calcium supplements, though there aren’t enough data to pinpoint the best dose or to identify which patients might most need the calcium, Dr. Schafer said. She recommended 1,200-2,000 mg/day (preferably in citrate form) after malabsorptive surgery and possibly after restrictive bariatric surgery such as adjustable gastric banding.
Based on the preoperative vitamin D level, prescribe 800-2,000 IU/day of vitamin D3 supplementation after malabsorptive surgery and possibly after restrictive bariatric surgery. "I’ve had people who need more" than that dose range, she added.
For postoperative surveillance, check calcium homeostasis laboratory tests every 6 months for the first 2 years and then annually after malabsorptive surgery and possibly after any bariatric surgery. The tests include calcium, albumin, phosphate, creatinine, 24(OH)D, and parathyroid hormone.
If the parathyroid hormone level is high, but the 25(OH)D level is low, treat with vitamin D supplementation. If the parathyroid hormone level is high and the 25(OH)D level is ideal, check the patient’s 24-hour urinary calcium, and if that is low, increase calcium intake.
Because some of the etiology of bariatric surgery–induced bone loss may be the preferential loss of lean mass over fat mass, or changes in fat distribution, encourage patients to consume protein and to exercise, she said.
The Endocrine Society recommends dual-energy x-ray absorptiometry (DXA) at baseline and annually in people who are undergoing malabsorptive bariatric surgery. No data show that such monitoring actually improves outcomes, "but I do think that you should consider it for any people who can fit on the DXA scan before the operation," Dr. Schafer said. The weight limit for the scanner is approximately 275-350 pounds.
Dr. Schafer also said that she advises a DXA scan 1-2 years postoperatively. Incorporate those results into "your clinical judgment and other risk factors like age or prior history of fractures to set up an individualized plan for monitoring bone density from there."
In general, high body mass index has been associated with high bone mineral density, and either voluntary or involuntary weight loss is associated with bone loss and increased fracture risk. Bariatric surgery leads to loss of bone mass for multiple reasons, she said, including nutritional deficiencies from malabsorption, the body’s signals about decreased skeletal loading with weight loss, and changes in fat-secreted hormone.
Most of the data on bone loss after bariatric surgery are for Roux-en-Y gastric bypass, which induces early and sustained increases in bone turnover and decreases in bone mineral density. Fewer data are available on other procedures, but a handful of studies suggest that another malabsorptive procedure, biliopancreatic diversion, may produce effects similar to those of gastric bypass, and that adjustable gastric banding may have less of an impact on bone, she said.
For gastric bypass, one study of 15 patients reported an 8% decrease in total hip bone mineral density within 9 months (J. Clin. Endocrinol. Metab. 2004;89:1061-5). Femoral neck bone density decreased by 9% within 1 year of gastric bypass in a separate study of 23 patients (J. Clin. Endocrinol. Metab. 2008;93:3735-40). A third study of 42 patients reported a 7% decrease in spine bone density and a 10% decrease in total hip bone density a year after gastric bypass (Obes. Surg.2009;19:41-6).