According to a new study, women who drank the most sweet soft drinks had a 78% increased risk of endometrial cancer.

Researchers have found that other sweet treats, such as baked goods, didn’t have an effect. Nor did natural fruit juice, even though it’s full of naturally occurring sugars.

The findings fit in with other research linking sugar intake, obesity and a lack of exercise with the cancer, which kills more than 8,000 US women a year.

“Other studies have shown increasing consumption of sugar-sweetened beverages has paralleled the increase in obesity. Obese women tend to have higher levels of estrogens and insulin than women of normal weight,” said Maki Inoue-Choi, who did the study while at the University of Minnesota and now is at the National Cancer Institute.

It has to do with how insulin, which controls how the body uses sugar, affects other hormones such as estrogen.

“Increased levels of estrogens and insulin are established risk factors for endometrial cancer,” Dr. Maki Inoue-Choi said.

Dr. Maki Inoue-Choi and colleagues studied the records of 23,000 middle-aged women who had gone through menopause. Endometrial cancer is more common in women past menopause.

The women had been taking part in a bigger study of diet, and regularly filled out questionnaires on what they ate and drank every day. They were specifically asked about Coke, Pepsi and other cola drinks; caffeine-free versions of these drinks; 7-Up and similar sugar-sweetened sodas, and other sugary drinks such as lemonade or Hawaiian Punch.

They were also asked about sugar-free drinks such as Fresca, Diet Ginger Ale and other beverages. And they were asked about cookies, brownies, doughnuts, candy and pies.

The researchers arranged the women into five groups, called quintiles, from those who ate none of these things a week to those who ate 60 or more servings a week.

Women who drank the most sweet soft drinks had a 78 percent increased risk of endometrial cancer

The women showed one known pattern – those who were older, weighed more, who had late menopause or had a history of diabetes were at higher risk of endometrial cancer, which is diagnosed in nearly 50,000 US women every year.

“In contrast, women who ever smoked or experienced a greater number of live births were at lower risk of endometrial cancer,” the researchers wrote in the journal Cancer Epidemiology, Biomarkers & Prevention, which is published by the American Association for Cancer Research.

Women who drank sugary drinks had a higher risk of the most common type of endometrial cancer, called Type I endometrial cancer. The more they drank, the higher the risk, the researchers found.

“The risk was 78% among women in the highest quintile of sugar-sweetened beverage intake,” they wrote.

Other studies have found that coffee and exercise reduce the risk, but Dr. Maki Inoue-Choi and colleagues did not.

“Fruit juice intake was not associated with the risk of Type I endometrial cancer,” they added.

“Similarly, neither sweet/baked good nor starch intake was associated with Type I endometrial cancer risk.”

It might not be anything special about sugary drinks, the researchers say. It might be that women who drink a lot of such drinks have other unhealthy habits, too.

And Inoue-Choi says it’s not clear why drinks and not other sweet foods showed an effect.

“One possibility is that sugar from whole foods comes with other nutrients, such as fiber,” she said in a telephone interview.

“Sugar from beverages doesn’t come with these nutrients.”

More research will be needed to tease out an explanation. But Dr. Maki Inoue-Choi notes that obesity is still, by far, the biggest risk factor for endometrial cancer, causing half of all cases.

Estrogen is one known cause of endometrial cancer, which affects the lining of the uterus. Women who take hormones, as in hormone replacement therapy, are usually given a form of progesterone, also, to protect against endometrial cancer.

Fat cells also secrete estrogen and that’s one reason why obesity can cause the disease, experts say.

There are two main types of endometrial cancer, according to the National Cancer Institute – Type I and Type II.

Dr. Maki Inoue-Choi and colleagues found that sweetened drinks only affected Type I risk. But Type I accounts for 80% of endometrial cancers.

It’s usually diagnosed early, in time for treatment, because in 90% of cases the woman has abnormal bleeding, the American Cancer Society says.