SoS: Women at Higher Risk of Osteoporosis After Weight Surgery

May 11, 2015

PRAGUE (updated May 15, 2015) — A new analysis of the Swedish Obesity Subjects (SoS) study has shown that women who undergo bariatric surgery are at increased risk of developing fractures and osteoporosis long term. The findings do not seem to apply to men who have weight-loss surgery.

Presenting the results May 9 at the 2015 European Congress on Obesity, Sofie Ahlin, MD, PhD, of the University of Gothenburg, Sweden, told attendees that "several studies have shown that bariatric surgery leads to a reduction in bone-mineral density in the femur 9 to 12 months after surgery."

However, until now there "have been very few studies investigating whether this leads to long-term risk of osteoporosis," she observed.

During a follow-up of as long as 25 years, women in the study who underwent one of three bariatric procedures were 1.5 times more likely to suffer any fracture compared with controls and significantly more likely to develop osteoporosis.

Dr Ahlin said that it is not clear what the cause of the increased risk of osteoporosis could be, with mechanical unloading, endocrine effects, or malnutrition all potentially implicated. The latter could play a role via malabsorption of certain vitamins and minerals — a known complication of more contemporary types of bariatric surgery.

The findings will require confirmation, she noted, but in the meantime ensuring that women in particular take vitamin and mineral supplements long term following weight-loss surgery is imperative, she said.

Asked to comment, cochair of the session, Dr Michael Suter, of the department of visceral surgery, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland, told Medscape Medical News that these new data must be taken seriously. However, there are some caveats, he noted. "Most patients in the SOS study have been operated on more than 10 years ago, some as long as 25 years ago, and overall care of bariatric patients has changed since these old days," he observed. And what the authors are presenting "is an association, but causation is not proven yet."

Dr Suter said it was also likely that "nutrient supplementation was probably suboptimal in the early days of the SOS study, [and] if causation is proven…micronutrients probably play a role, especially calcium and vitamin D3."

"What we certainly must do is make sure our patients are well supplemented, especially with calcium and vitamin D, so that they do not develop secondary hyperparathyroidism," he added. This sometimes requires very high dosages of supplements, he explained, "but it can be achieved in the vast majority of patients who attend follow-up visits and lab tests regularly and who take their supplements. I personally give routine supplements plus additional ones based on lab tests."

Dr Sigrid B Gribsholt, from Aarhus University Hospital Copenhagen, Denmark, said this new analysis of SoS means osteoporosis may need to be added to the list of complications that women in particular, who make up 80% of bariatric-surgery patients, need to be made aware of.

"It should not be a cosmetic procedure," she commented — potential candidates should be properly informed during counseling of all the potential risks involved and steps they can take to help limit complications, with only appropriate patients selected for the operation, she stressed.

And in Denmark, it is routine policy to encourage bariatric-surgery patients to take a vitamin and mineral supplement long term following weight-loss surgery, she noted.

No Increased Risk of Fractures and Osteoporosis Among Men

The nonrandomized, case-matched, prospective SoS study is one of the longest-running trials of bariatric surgery to date and has generated many presentations at international conferences and journal articles.

It began in 1987 and is following 2010 individuals aged 37 to 60 years old with a body mass index of more  than 34 kg/m2 for men and more than 38 kg/m2 for women who underwent bariatric surgery at one of 25 surgical centers in Sweden between 1987 and 2001.

Of the subjects, 376 (19%) had gastric bands fitted, 265 (13%) had gastric bypass, and 1369 (68%) had vertical banded gastroplasty; the latter procedure is hardly ever performed these days.

The participants were compared with a group of 2037 controls, matched for 18 variables.

To assess the effects of surgery on fractures and osteoporosis, which were not prespecified outcomes, Dr Ahlin and colleagues obtained information by cross-checking social security numbers from the SoS study with ICD9/ICD10 codes for osteoporosis and fractures in the Swedish national health registers database.

Smoking status, age at menopause in women, and physical activity was obtained from questionnaires at prespecified time points.

During follow-up, there were 187 fractures among the surgery group compared with 127 among controls (P < .001), for a hazard ratio (HR) of 1.53 following adjustment for age, sex, smoking, alcohol intake, and fracture before baseline.

When the analysis was performed by gender, it became apparent the women who had had weight-loss surgery were at significantly increased risk of fracture compared with controls (HR, 1.69; P < .001). For men, this figure was 1.21 and was not significant (P = .349)

They then went on to examine the cumulative incidence of osteoporosis and found that women in the surgery group were almost three times more likely to have developed this condition — 47 individuals compared with 19 female controls (HR, 2.73; P < .001). Again, this comparison was not significantly different among the men who had undergone bariatric surgery compared with controls (HR, 2.19; P = .264).

"Our results indicate that bariatric surgery causes long-term effects on bone health with an increased risk of fracture and osteoporosis in women," Dr Ahlin said.

She noted also that there may be implications for teenagers, more and more of whom are undergoing weight-loss operations. For example, "What happens to bone health in adolescents after bariatric surgery?" It will be important to investigate this further, she concluded.

Gastric Bypass Has Highest Risk of Osteoporosis; No Information on Sleeve Gastrectomy

Dr Suter observed that malabsorption of vitamins and minerals was not a complication of the most commonly performed procedure in SoS, vertical banded gastroplasty, "which was purely a restrictive surgery" that is hardly ever performed nowadays.

He wondered if — given the theory that nutrient deficiency may be the cause — the researchers had looked at fracture and osteoporosis rates by surgery type.

Dr Ahlin said they had done a "preliminary" analysis, and "it is the [gastric]-bypass group that has the highest risk, so it might be [due to] malabsorption."

Dr Suter said that since there were very few patients with gastric bypass in SoS, it is probably too early to draw a definitive conclusion regarding osteoporosis and this surgical procedure, and the data certainly "do not apply to sleeve gastrectomy, since no patient in that study [SoS] had a sleeve."

But "What we may worry about is, considering that SoS mostly includes patients who had restrictive surgery, the results might be worse after gastric bypass or sleeve gastrectomy, but we have no data to support this fear at the present time," he commented.

He also pointed out that the authors do not give any explanation as to why the finding of more osteoporosis and more fractures appears to have affected women but not men.

"I guess that we need to have more results before we draw definitive conclusions, and we certainly need to have more than just an association, but also explanations about the mechanisms if causation is proven," he concluded.

Dr Ahlin and Dr Suter reported no relevant financial relationships.

2015 European Congress on Obesity. May 9, 2015. Abstract T8:OS3.3.


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