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BMD loss, not vitamin D changes, observed after bariatric surgery

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June 29, 2017

Patients with obesity who underwent bariatric surgery did not experience a decline is serum 25-hydroxyvitamin D levels over 12 months vs. controls who did not have surgery, but significant reductions in bone mineral density and a trend toward increased fracture risk in the bariatric surgery group were observed, according to findings from a meta-analysis.

“With a large amount of bariatric procedures performed worldwide — now even expanding to patients with lower BMI — it is imperative to better understand the potential negative effects of bariatric surgery on bone metabolism,” Aashish Kalani, MD, of the department of internal medicine at McMaster University in Hamilton, Ontario, Canada, and colleagues wrote. “[A] paucity of high-quality studies underscores a significant care and knowledge gap. There need to be appropriate screening protocols in place to detect 25-(OH)D deficiency, as well as ensure early and adequate supplementation. Recognizing some of these more vulnerable patients can help drive the implementation of preoperative BMD [tests], especially given that a significant portion of these persons with obesity are already osteoporotic before surgery.”

Kalani and colleagues analyzed data from 4,282 patients from five controlled observational studies and two randomized controlled trials conducted in Switzerland, Taiwan, the United Kingdom and the United States between 2004 and 2015. Included studies compared patients with obesity who underwent bariatric surgery (3,153 women) with patients with obesity who did not undergo surgery (controls; n = 15,630), assessing change in 25-(OH)D levels from baseline to 12 months after surgery. Secondary outcomes included change in 25-(OH)D levels at 24 months, incident self-reported fractures at 24 months and change in total hip and lumbar spine BMD at 12 and 24 months. The mean age of the patients was 40 years in six of seven studies; patients in four of seven studies had baseline BMI of at least 40 kg/m². Risk of bias across studies was low, according to researchers.

In three studies comparing between-group differences in 25-(OH)D levels, researchers observed no differences between surgery patients (n = 74) and controls (n = 58) at 12 months (weighted mean difference = 6.79%; 95% CI, –9.01 to 22.59). Results persisted at 24 months between the surgical group (n = 40) and controls (n = 28; weighted mean difference = 51.6%; 95% CI, –36.18 to 139.39).

In four studies assessing incident, self-reported fractures, researchers observed a trend toward increased fracture risk in patients who underwent surgery (n = 6,811) vs. controls (n = 25,285) at 12 months, with a RR of 1.24 (95% CI, 0.99-1.56).

In two studies assessing total hip BMD via DXA, patients who underwent surgery experienced a decrease in total hip BMD vs. controls at 12 months (weighted mean difference = –7.33%; 95% CI, –8.7 to –5.95) and 24 months (weighted mean difference = –9.69%; 95% CI, –11.6 to –7.78). Three studies assessing lumbar spine BMD also showed a similar decrease for patients who underwent surgery vs. controls at both 12 months (weighted mean difference = –1.73%; 95% CI, –3.56 to 0.11) and 24 months (weighted mean difference = –5.18%; 95% CI, –10.84 to 0.48), according to researchers.

“Here, there was no change in 25-(OH)D levels, a trend toward increased fracture rates, and decreased BMD at the [total hip] with a trend toward decreased BMD at the [lumbar spine] in bariatric surgery patients,” the researchers wrote. “The lack of difference in 25-(OH)D is not fully consistent with what has been previously observed in the literature, which may be due to the heterogeneity between studies.”

The researchers also noted that the level of 25-(OH)D supplementation following bariatric surgery varied across studies. – by Regina Schaffer

Disclosures: One study author reports receiving grants and personal fees from Actavis, AgNovos, Amgen, Eli Lilly and Merck; another author reports receiving honoraria or speaking fees from Amgen and Eli Lilly.