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Swedish Obese Subjects study

Bariatric surgery prevents cardiovascular events

Diabetes or related risk factors were a strong indicator of surgical benefit. Photo: istockphoto
Non-randomised study found 30% reduction in incidence of heart attacks and strokes after surgery
No significant relationship found between weight change and cardiovascular events
Some benefits of bariatric surgery “independent of the degree of surgically induced weight loss”

Patients who undergo gastric bypass surgery are less likely to die from cardiovascular events than people who receive more conventional treatment for their weight condition, according to the latest results from the Swedish Obese Subjects (SOS) study published in the Journal of the American Medical Association.

“Bariatric surgery was associated with about a 30% reduction in the incidence of both heart attacks and strokes,” said researcher Professor Lars Sjostrom, University of Gothenburg, Sweden. “While pre-surgery BMI did not predict surgical health outcomes, having diabetes or risk factors for diabetes was a strong indicator of surgical benefit. This could have implications for selecting candidates for weight loss surgery.”

Swedish Obese Subjects

The SOS study is an ongoing, non-randomised, prospective, controlled study conducted at 25 public surgical departments and 480 primary health care centres in Sweden, and includes 2,010 obese participants who underwent bariatric surgery and a control group of 2,037 matched obese controls who received usual care.

The research is testing the hypothesis that bariatric surgery is associated with a reduced incidence of cardiovascular events and examining the relationship between weight change and cardiovascular events.

Patients were recruited between September 1987 and January 2001. The date of analysis was December 2009, with median follow-up of 14.7 years. Inclusion criteria were age 37 to 60 years and a body mass index of at least 34 in men and at least 38 in women.

Surgery patients underwent gastric bypass (13.2 per cent), banding (18.7 per cent), or vertical banded gastroplasty (68.1 per cent), and controls received usual care in the Swedish primary health care system. Physical and biochemical examinations and database cross-checks were undertaken at pre-planned intervals. 

The average changes in body weight after 2, 10,15, and 20 years were 23 per cent, 17 per cent, 16 per cent, and 18 per cent in the surgery group and 0 per cent, 1 per cent, 1 per cent, and 1 per cent in the control group, respectively.


During follow-up, there were 49 cardiovascular deaths among the patients in the control group and 28 cardiovascular deaths among the patients in the surgery group (adjusted hazard ratio [HR], 0.47; 95% CI, 0.76-0.29; p=0.002). In total (fatal and non-fatal), there were 234 cardiovascular events among patients in the control group and 199 cardiovascular events among patients in the surgery group (adjusted HR, 0.67; 95% CI, 0.54-0.83; p<0.001).

After adjustment for a number of variables, bariatric surgery was associated with a reduced number of fatal cardiovascular deaths and a lower incidence of total cardiovascular events.

Bariatric surgery was associated with reduced number of fatal heart attack deaths (22 in the surgery group vs. 37 in the control group), with analysis indicating that bariatric surgery was related both to reduced fatal heart attack incidence and total heart attack incidence. Bariatric surgery was also associated both with reduced number of fatal stroke events and total stroke events.

Interestingly, the researchers found no significant relationship between weight change and cardiovascular events in the surgery or control group. They suggest that the lack of association between weight loss and reduction of cardiovascular events could be related to inadequate statistical power to detect this relationship. 

“Alternatively, following relatively modest weight loss induced by bariatric surgery, there is no further risk reduction attributable to greater, subsequent weight loss,” the authors said. “Our negative findings also emphasise the need to explore weight loss independent of effects of bariatric surgery."

“In conclusion, this is the first prospective, controlled intervention to our knowledge reporting that bariatric surgery is associated with reduced incidence of cardiovascular deaths and cardiovascular events.

“These results - together with our previously reported associations between bariatric surgery and favourable outcomes regarding long-term changes of body weight, cardiovascular risk factors, quality of life, diabetes, cancer, and mortality - demonstrate that there are many benefits to bariatric surgery and that some of these benefits are independent of the degree of the surgically induced weight loss."


In an accompanying editorial, Dr Edward H Livingstone, University of Texas Southwestern Medical Center, Dallas, USA, argues that the benefits from bariatric surgery are not related to weight loss, the main reason these operations are performed. He also adds that the absolute difference in cardiovascular events and deaths between the surgery and non-surgery groups in these latest SOS data was small. 

“Obese patients who are otherwise healthy should not have bariatric surgery, because the expected health benefits do not necessarily exceed the risks of weight-loss operations,” he concludes. “People with abdominal obesity may be at higher risk for heart problems than people with higher fat mass in the trunk and legs. It may be time for experts to reconsider the criteria for recommending bariatric surgery and to rigorously assess the available evidence and provide updated recommendations for bariatric procedures for the treatment of obesity.”

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