A large retrospective study that focused mainly on women finds that cancer risk is reduced by almost a third after bariatric, or weight loss, surgery.

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Weight loss surgery is associated with a significantly lower risk of cancer in women, a new study shows.

According to the National Cancer Institute, in the United States, approximately 72,000 new cases of cancer in women and 28,000 in men were caused by excess weight in 2012.

It is also estimated that over a third of U.S. adults live with obesity, though more women are affected than men.

A new retrospective study from the University of Cincinnati College of Medicine in Ohio has now analyzed the data of more than 22,000 people who underwent bariatric surgery, to check for impact on the risk of developing cancer.

The data were sourced from five different Kaiser Permanente centers: in Colorado, in Northern California, in Oregon, in Southern California, and in Washington, D.C.

“We found,” says lead researcher Dr. Daniel Schauer, “[that] having bariatric surgery is associated with a reduced risk of cancer, especially obesity-associate[d] cancers including postmenopausal breast cancer, endometrial cancer, pancreatic cancer, and colon cancer. What’s surprising is how great the risk of cancer was reduced.”

The study’s findings were published in the Annals of Surgery.

Dr. Schauer and his team compared the medical data of 22,198 people who had undergone weight loss surgery between 2005 and 2012 with that of 66,427 individuals who did not go through surgery. Over 80 percent of the total cohort were women.

The researchers used statistical models to investigate the incidence of cancer in people who had bariatric surgery for up to 10 years following the procedure. They also took into account the cohort who did not opt for surgery.

The two groups were matched for relevant impacting factors, including sex, age, and body mass index (BMI).

All the people whose data were analyzed were followed-up for medical outcomes until 2014. Dr. Schauer and team identified a total of 2,543 incident cancers “after a mean follow-up of 3.5 years.”

The researchers found that bariatric surgery led to a 33 percent lower risk of any type of cancer, but the greatest benefit was observed for cancers associated with obesity.

More specifically, among those who had undergone bariatric surgery, there was a 42 percent lower risk of postmenopausal breast cancer and a 50 percent lower risk of endometrial cancer. The risk of colon cancer was also 41 percent lower, and the risk of pancreatic cancer dropped by 54 percent.

One explanation given by the scientists for the reduced risk of developing certain obesity-related cancers was tied to modified levels of estrogen, a hormone predominantly linked to the development of the female reproductive system.

“Cancer risks for postmenopausal breast cancer and endometrial cancer are closely related to estrogen levels,” explains Dr. Schauer. “Having weight loss surgery reduces estrogen level[s].”

Another explanation is that weight loss surgery also reduces insulin resistance and lowers the risk of diabetes, which is a risk factor for pancreatic cancer.

Also, although the risk of cancer was significantly lowered in women post-surgery, no such association was confirmed for men.

But Dr. Schauer suggests that this may be due to the high percentage of women in this study. Another possible explanation may be that the greatest benefit was noted in relation to postmenopausal breast cancer and endometrial cancer, which are specific to women.

In the end, they suggest that a lower cancer risk may be a significant motivating factor to undergo bariatric surgery for individuals living with obesity, yet it is only one reason why this course of action should be seriously considered.

“I think considering cancer risk is one small piece of the puzzle when considering bariatric surgery, but there are many factors to consider,” adds Dr. Schauer.

Reductions in diabetes [and] hypertension and improvements in survival and quality of life are reason enough. The study provides an additional reason to consider bariatric surgery.”

Dr. Daniel Schauer