番茄社区

BOSTON -- Anatomical changes due to bariatric surgery can put patients at risk for mineral deficiencies and subsequent osteoporosis, and managing this risk can pose a challenge for healthcare providers.

"Many forms of bariatric surgery lead to malabsorption of calcium and vitamin D, which can cause secondary hyperparathyroidism in the absence of treatment," Elaine W. Yu, MD, of Massachusetts General Hospital in Boston, explained to 番茄社区.

However, the degree of fracture risk following bariatric surgery varies based on the specific procedure.

"Mixed restrictive and malabsorptive procedures such as Roux-en-Y gastric bypass (RYGB) and biliopancreatic diversion (BPD) are associated with an increased risk of fracture at osteoporotic sites, risk that starts to manifest between 2 and 5 years after surgery," Anne Schafer, MD, of the University of California San Francisco and the San Francisco VA Healthcare System told 番茄社区. "Laparoscopic adjustable gastric banding (LAGB) appears not to increase fracture risk, at least in the short term, and it is not possible at this point to determine whether sleeve gastrectomy increases fracture risk."

While sleeve gastrectomy may also cause bone loss, it's perhaps to a lesser degree than BPD or RYGB, Yu said.

Schafer said that "the literature is largest and strongest for RYGB" mostly because it was the reigning bariatric procedure in popularity until recently.

"After RYGB, bone mineral density declines at the axial and appendicular skeleton, and there are detrimental effects on bone microstructure and estimated strength. Postmenopausal women seem to be particularly affected," she noted.

As for screening, the released by the American Association of Clinical Endocrinologists (AACE), the Obesity Society, and American Society for Metabolic and Bariatric Surgery (ASMBS) state that DXA bone density scans are indicated both preoperatively and 2 years after bariatric surgery.

"In particular, I recommend screening patients who are at higher risk for low bone density, such as postmenopausal women, older men, and those with prior fragility fractures or a family history of osteoporosis," Yu said.

This recommendation was echoed by Schafer, who added, "I believe DXA may be appropriate preoperatively in higher-risk patients, including postmenopausal women, men ages >50 years, and others with risk factors for osteoporosis. It could also be considered postoperatively, perhaps after 2 years, in select patients."

In addition to screening bariatric surgery patients for bone changes, clinicians must also closely monitor calcium and vitamin D levels before and after surgery.

"Especially considering that patients with obesity are at high risk of vitamin D deficiency, one should measure serum 25-hydroxyvitamin D (25OHD) level and correct vitamin D deficiency preoperatively. Postoperatively, routine monitoring of serum 25OHD, calcium, albumin, and parathyroid hormone (PTH) levels is indicated. The recommended frequency of these measurements varies between guidelines, but one reasonable approach is to do routine biochemical screening every 6 months for the first 2 years and then annually," Schafer said.

She recommended that providers refer to the guidelines of the ASMBS when considering calcium and vitamin D supplementation for these patients.

"Calcium citrate is preferred over calcium carbonate," Schafer said, adding that it should be administered with split doses to achieve a total daily calcium intake -- including diet plus supplements -- of 1,200 to 1,500 mg per day in patients who underwent RYGB, sleeve gastrectomy, or LAGB. Patients who underwent BPD should aim to achieve a total intake of 1,800 to 2,400 mg daily, she added.

"These intakes may not be sufficient for a substantial proportion of patients, at least after RYGB and BPD, and thus monitoring with PTH (and 24-hour urinary calcium when appropriate) is important," Schafer noted.

She also suggested that "a typical initial vitamin D supplement dose is 3,000 IU of vitamin D3 daily, with titration to serum 25OHD >30 ng/mL."

Lifestyle modification after bariatric surgery is important for these patients in order to mitigate the adverse impact on their bones. Other recommendations include a diet sufficient in protein and regular physical activity.

In some bariatric surgery patients at a moderate to high fracture risk, antiresorptive osteoporosis therapies may also be appropriate. However, in order to minimize the risk of hypocalcemia, "an antiresorptive should be used only after vitamin D and calcium supplementation is deemed sufficient based on measurement of serum 25OHD, corrected calcium, PTH, and potentially 24h urinary calcium," Schafer said, explaining that the parenteral route is preferred over oral treatment.

This recommendation was reinforced by Yu, who suggested that providers "avoid oral bisphosphonates due to theoretical problems with absorption and potential for increased risk of GI adverse effects. Intravenous bisphosphonates and/or denosumab could be cautiously considered as long as providers ensure appropriate calcium and vitamin D supplementation to avoid hypocalcemia."

She also said that healthcare providers must emphasize to patients prior to bariatric surgery that calcium and vitamin D supplements are "lifelong requirements" following surgery.

"I want to reiterate the call for bone density screening in this population -- in an analysis that we published, only around at any point after surgery," Yu noted.

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