WASHINGTON, Aug. 23 (Xinhua) -- An extensive Swedish study has established that surgery reduces premature death in patients with severe obesity.

    The research has shown that mortality is significantly lower among patients who undergo surgery than among those who do not.

    The results were published Thursday in The New England Journal of Medicine.

    "We show for the first time that surgery against obesity not only leads to long-term loss of weight, it also significantly reduces mortality," said Lars Sjostrom, professor emeritus at the Sahlgrenska Academy in Sweden.

    Over 4,000 severely obese patients were included in the study, which researchers started as long ago as 1987. Half of these patients underwent stomach surgery (bariatric surgery) intended to cause weight loss.

    The remaining patients received advice concerning changes in lifestyle in order to lose weight. Some of these patients also received medicine for weight loss, but even so, the conventional treatment was considerably less effective than the surgical procedure.

    The group receiving conventional treatment had even increased somewhat in weight after 10 years, while patients who had undergone surgery decreased in weight by 16 percent, on average.

    "Bariatric surgery is the only treatment for severe obesity for which there is scientific evidence that it reduces mortality", said Lena Carlsson, professor at the Sahlgrenska Academy.

    A long-term follow up study for between five and 18 years on the patients who had undergone surgery showed that mortality among these patients was 29 percent lower than it was among the other patients.

    The researchers also considered the effects of many biochemical and other variables in the analysis, including smoking, stress and previous medical history.