Surgery decreases long-term mortality, morbidity, and health care use in morbidly obese patients.

To the Editor: Christou and colleagues recently reported in a prospective cohort study that 1035 patients who underwent gastric bypass had lower morbidity and mortality, as well as lower health care costs than 5746 control subjects matched by age, gender, and date of diagnosis of morbid obesity. These are impressive findings. We write to seek clarification about the characteristics of the matched-control subjects. The report states that “patients were excluded secondary to previous diagnosis and admission to hospital for 1 of the chronic conditions listed in Table 4 for the 6 months prior to surgery.” Thus, although the authors excluded patients with certain medical conditions who were hospitalized, they did not match control patients to surgery patients on the presence of comorbidity. This leaves open the possibility of confounding. If the authors only excluded patients who were hospitalized for obesityrelated illness, then there is potential for confounding by comorbidity. Patients who underwent surgery may have had fewer preoperative obesity-related diseases, which may have resulted in lower mortality during follow-up. In the Swedish Obese Subjects (SOS) study, the presence of obesity-related illness was included in the matching of bariatric surgery patients to control patients. As the authors note, weight loss in the SOS was considerably smaller, which may account for the favorable findings of the present study. However, the current results cannot be fully judged until knowing whether the surgery and control samples were matched on preoperative obesity-related illnesses. One additional issue is that the authors did not control for socioeconomic status (SES) in their analyses. Although the single-payer Canadian health care system does not charge patients for the surgical procedure (ie, access to the procedure should not differ by social class), it is known that higher SES is strongly and independently associated with better health status and with lower mortality. It is certainly possible that higher SES individuals were more likely to undergo the surgery, and thus, to have better health outcomes and lower healthcare costs. The reductions in weight, morbidity, mortality, and healthcare costs achieved by the bariatric surgery patients in this study are impressive. An additional strength of the article is that it is a true effectiveness study, with patients drawn from regular clinical practice settings. However, the methods used for matching generate concern for the possibility of uncontrolled confounding either by comorbidity or by socioeconomic status. If the authors are able to address these concerns, it would greatly strengthen the case for the longterm clinical and economic benefits of weight reduction.