Clinical Pearls & Morning Reports

Posted by Carla Rothaus

Published October 14, 2020


What were the recently reported results of the Swedish Obese Subjects study regarding life expectancy among participants who underwent bariatric surgery? 

Carlsson et al. recently published additional results of the Swedish Obese Subjects
study, which compared mortality and life expectancy among patients treated with either bariatric surgery (surgery group) or usual obesity care (control group) in the Swedish Obese Subjects study and participants in the Swedish Obese Subjects reference study (reference cohort), a random sample from the general population. Read the NEJM Original Article here

Clinical Pearls

Q: What are the known benefits of bariatric surgery?

A: Bariatric surgery generally leads to durable weight loss and reduces the risk of cardiovascular disease, type 2 diabetes, and cancer. While bariatric surgery has beneficial effects for many, a recent retrospective study indicated that the relative risk of death remained higher among patients who underwent bariatric surgery than in the general background population.

Q: What is the Swedish Obese Subjects (SOS) study?

A: In brief, 2010 participants in Sweden who underwent bariatric surgery and 2037 matched controls were recruited between September 1, 1987, and January 31, 2001. The inclusion criteria were an age between 37 and 60 years and a body-mass index (BMI) of at least 34 for men and at least 38 for women. In 2007, the authors reported that bariatric surgery reduced overall mortality — the primary end point in the prospective, controlled SOS study — by 29% over a mean follow-up of 10.9 years. The current report includes an assessment of mortality and life expectancy after an additional 13 years of follow-up.

Morning Report Questions

Q: What were the recently reported results of the SOS study regarding life expectancy among participants who underwent bariatric surgery?

A: In this study, bariatric surgery was associated with lower overall mortality than usual obesity care. In middle-aged patients with severe obesity, life expectancy was approximately 3 years longer among patients who underwent surgery than among those who received usual care. It is important to emphasize that the reported gain in life expectancy is for the entire study population and cannot be translated into a survival benefit for a particular patient or for other populations beyond the study participants. In the surgery group, the median life expectancy was 5.5 years (95% CI, 3.4 to 7.6) shorter (adjusted difference) than in the reference cohort (P<0.001). Possible explanations for the remaining higher mortality in the surgery group include the above-normal BMI even after bariatric surgery, irreversible effects of obesity-related metabolic dysfunction that may have begun processes that lead to atherosclerosis or microvascular disease, and surgical complications and other factors causing death (alcoholism, suicide, and trauma). More frequent occurrence of alcoholism, suicide, and trauma and a larger number of related deaths have previously been observed among patients with obesity who undergo bariatric surgery than among those who do not undergo surgery.

Q: What were the main causes of death among patients in the bariatric surgery group in the SOS study?

A: Since life expectancy was shorter in the surgery group than in the reference cohort, the authors compared causes of death between these groups to determine which life-threatening diseases remained overrepresented in the surgery group. The hazard ratio for death from cardiovascular causes in the surgery group as compared with the reference cohort was 2.64 (95% CI, 1.78 to 3.91); the most common cardiovascular causes of death were myocardial infarction, heart failure, and sudden death. The hazard ratio for noncardiovascular causes of death in the surgery group as compared with the reference cohort was 1.50 (95%, 1.18 to 1.91); these causes of death were mainly infections, complications after surgery, and other factors (alcoholism, suicide, and trauma).

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