Weight-loss surgery may help obese women lower their risk of developing cancer, Swedish researchers said on Tuesday.

They found women who had weight-loss surgery were 42 percent less likely to develop cancer during a 10-year study published in the journal Lancet Oncology.

Men in the study did not benefit, possibly because many cancers are driven by female hormones such as estrogen, they said, or simply because fewer men get weight-loss surgery.

Obesity has long been known to raise the risk of cancer, and the evidence continues to mount.

A study released on Tuesday in the Journal of the American Medical Association found people who were obese as young adults had twice the risk of developing pancreatic cancer, an especially aggressive kind.

Weight-loss operations -- in which doctors change the digestive system's anatomy to cut the volume of food a person can eat -- have been shown to reverse diabetes and reduce the risks of dying from heart disease.

The Swedish study, led by Lars Sjostrom of Sahlgrenska University Hospital in Gothenburg, compared 2,010 obese patients who had weight-loss surgery with 2,037 obese patients who got standard diet and exercise treatment.

Overall, they found the surgery helped people maintain an average weight loss of 19.9 kg or about 43 pounds over 10 years. People in the diet and exercise group gained an average of 1.3 kg or nearly 3 pounds during the study period.

The surgery cut the rates of cancer by a third, but women enjoyed most of that benefit. Among women, there were 79 first-time cancers in the surgery group, and 130 among those who got standard treatment.

Dr. Andrew Renehan of the University of Manchester in the United Kingdom said in a commentary the absence of a benefit in men could simply reflect the number of men who were in the study.

He said for women, the greatest cancer prevention effects were likely to be post-menopausal breast and endometrial cancers -- cancers sensitive to hormone levels.

Renehan said the effects of weight-loss surgery may take longer to show up in men, who are more prone to colon, rectal and kidney cancers, which take longer to become apparent.

Dr. Leena Khaitan, a bariatric surgeon at University Hospitals Case Medical Center in Cleveland, said the fact that men did not benefit likely reflected who gets the surgery.

"We know 80 percent of patients who undergo weight-loss surgery tend to be women. I suspect if we had larger numbers of men, we would probably see a difference," Khaitan said.

She said the study and others like it suggested bariatric, or weight-loss, surgery may be an important way to prevent costly, chronic diseases like cancer. It's a strong argument for preventive medicine."

She said many patients who qualify for the surgery do not get it because of problems with insurance coverage, but that may be short-sighted.

A study last year in the American Journal of Managed Care funded by Johnson & Johnson, a maker of bariatric surgery instruments, found insurers recoup the costs of weight-loss surgery within two to four years as obese patients become healthier and have fewer medical problems.

星期二，瑞典研究人员声称减肥手术可能可以帮助肥胖妇女降低癌症发病率。

在《柳叶刀肿瘤学》杂志发表的一份十年的研究报告上称，他们发现接受过减肥手术的女性发生癌症的机率降低了42%。

他们说这份研究没有惠及男性，可能是因为很多癌症由女性荷尔蒙如雌激素等引发，或者仅仅因为较少男性接受减肥手术。

据知肥胖一直能够提高癌症发生机率，这样的证据还在不断增加。

《美国医学会》杂志星期二发布的一份研究发现年轻时肥胖的人群发生胰腺癌（极为恶性的肿瘤）的机率是正常人群的两倍。

减肥手术——医生通过消化系统的解剖来减少病人的食物摄取量——已经证明可以治愈糖尿病，并且降低心脏病的死亡机率。

瑞典哥德堡市萨赫尔格雷斯卡(Sahlgrenska)大学医院的Lars Sjostrom领导的研究对比了2010个接受过减肥手术的肥胖病人与2037个接受正常饮食与锻炼疗法的肥胖病人。

总的来说，他们发现手术帮助病人保持了在十年内平均减重19.9kg或大约43磅。而正常饮食与锻炼组的病人在研究期间平均增重了1.3kg或接近3磅。

手术使癌症发病率降低了1/3，但这种降低主要体现在女性升上。在女性中间，手术组的有79人首次发现癌症，而正常治疗组的有130人得病。

英国曼彻斯特大学的Andrew Renehan博士在一份评论中说，男性不曾受益只能反映研究中的男性数目。

他说对于女性而言，预防癌症的最大效用可能在于预防绝经期后的乳腺癌或子宫癌——这些癌症对荷尔蒙水平很敏感。

Renehan说减肥手术的效用在男性身上可能需要更长时间才能显现，因为男性更倾向于患上结肠癌，直肠癌或肾癌——这些癌症需要更长时间显现。

美国克利夫兰大学医院病例医学中心的肥胖症外科医生Leena Khaitan博士说男性没有受益可能反映了接受手术的人。

Khaitan说：“我们知道接受减肥手术的病人80%是女性。如果男性占比增加了，我们可能就会看到不同。”

她说这个研究和其他类似研究暗示了减肥手术可能是一种重要的防治昂贵的慢性疾病如癌症的方法。

“在预防医学界这有很大争议。”

她说很多有资格接受手术的病人由于保险责任范围的问题不能接受手术，但那可能是一种短视行为。

去年美国杂志《管理式医疗护理》刊发的一份由Johnson&Johnson（减肥手术设备的制造商）资助的研究发现保险公司愿意赔偿减肥手术的费用，只要术后两到四年内肥胖病人变得更健康、更少医疗问题。