Obesity-related cancers usually seen in the elderly are appearing at higher rates in millenials at increasingly younger ages, according to a study published Monday in the Lancet.

The study is the first to systematically examine trends in obesity-related cancers in young adults in the U.S., according to a statement from the authors.

After examining data on 30 different cancers for 67 percent of the U.S. population over a 20-year period (from 1995-2015), the study, funded by the American Cancer Society and the National Cancer Institute, found that the risk of pancreatic, colorectal, endometrial, and gallbladder cancers in millennials is significantly higher than the risk Baby Boomers were facing when they were the same age.

“The risk of cancer is increasing in young adults for half of the obesity-related cancers, with the increase steeper in progressively younger ages,” co-author Ahmedin Jemal, vice president of Surveillance and Health Services Research for the American Cancer Society, told CNN.

Obesity has been repeatedly linked to increased risk of certain cancers. The World Health Organization has called obesity a "rising epidemic", with over 1 billion adults considered obese worldwide. The National Institute of Diabetes and Digestive Diseases reports that two in three U.S. adults are considered to be overweight or obese. A poor diet high in processed food, and low exercise rates have contributed to the obesity epidemic among millenials.

“Excess body weight is a known carcinogen, associated with more than a dozen cancers and suspected in several more,” the study authors wrote. “Growing evidence supports an association between childhood or adolescent obesity and increased risk of colorectal, endometrial, and pancreatic cancers and multiple myeloma.”

Research isn’t definitive on how exactly obesity is linked to cancer, but numerous studies have linked lower body weight to less cancer risk, and side effects of obesity to certain types of cancer. Obese people are known to have chronic low-level inflammation, which can, over time, cause DNA damage that leads to cancer. Obesity increases the risk of gallstones, which are strongly associated with a higher risk of gallbladder cancer. Fat tissue produces excess estrogen, high levels of which have been associated with increased risks of breast, endometrial, and ovarian cancer.

“In adults aged 30 years and older in the USA, excess bodyweight could account for up to 60 percent of all endometrial cancers, 36 percent of gallbladder cancers, 33 percent of kidney cancers, 17 percent of pancreatic cancers, and 11 percent of multiple myelomas in 2014,” the report said.

The authors warned that this could set back recent progress in fighting cancer mortality. Overall cancer rates have been declining for men and leveling out for women for the past few decades, but this new data suggests that decline might be temporary.

“Cancer trends in young adults often serve as a sentinel for the future disease burden in older adults, among whom most cancer occurs,” said Jemal.