By Jamie Ducharme
Updated: February 4, 2019 1:34 PM ET

The rates of new cancer cases and cancer deaths have fallen in the U.S. over the past few decades. But certain cancers are becoming more common among younger Americans, and researchers think obesity may be to blame, finds a new report from the American Cancer Society and the National Cancer Institute.

Obesity rates have been rising across age groups for years. According to the latest federal numbers, almost 36% of American adults ages 20-39 are obese, and that number may soon be even higher. Recent research suggests that if obesity trends continue, 57% of children in the U.S. will be obese by the time they turn 35.

Rates of six different cancers that are associated with obesity increased among adults ages 25-49 from 1995 to 2014, according to the research, which was published in the journal Lancet Public Health and based on information in the Cancer in North America database. These cancers include multiple myeloma, colorectal, endometrial, gallbladder, kidney and pancreatic.

Even though cancer most often strikes older adults, the sharpest increases were found in younger age groups. Pancreatic cancer exemplifies the pattern: From 1995 to 2014, incidence of the disease rose by 0.77% annually among adults ages 45-49; by 2.47% among those ages 30-34; and by 4.34% among those ages 25-29. Kidney cancer had the sharpest annual increase for young Americans: 6.23% from 1995 to 2014.

While some cancers have a fairly clear cause — like smoking for lung cancer, or HPV for cervical cancer — many are brought on by a confluence of chance, genetics and lifestyle and health factors. Obesity is among the most impactful of these. Research has linked excess body weight to about 40% of cancer cases in the U.S., and it’s a risk factor for common types like breast, ovarian and liver cancer, as well as those highlighted in the new study. By 2014, obesity accounted for 60% of endometrial cancers, 36% of gallbladder cancers, 33% of kidney cancers, 17% of pancreatic cancers and 11% of multiple myeloma among adults ages 30 and older, the new paper says.

Excess weight may promote cancer in several ways. It can increase inflammation, which is a risk factor for a number of chronic conditions and has been found to fuel cancer cell growth. Obesity may also alter levels of sex and growth hormones, as well as insulin, which can spark growth factors that allow cancer cells to proliferate. And some fattening foods, such as processed meats and snacks, have been independently linked to cancer risk.

It’s not possible to definitively attribute the recent cancer increases to obesity — but the new report notes that the upticks in cancer for young people coincided with a doubling in rates of childhood and adolescent obesity between 1980 and 2014, making weight a likely contributor. Only two types of non-obesity-related cancer, leukemia and a type of lower stomach cancer, increased among younger age groups during the study, suggesting that all cancer rates are not rising in this population.

Healthcare providers should be vigilant about screening for and helping patients try to prevent obesity, since the consequences of climbing cancer rates could threaten decades of public health progress, the authors say.

“The future burden of these cancers might be exacerbated as younger cohorts age, potentially halting or reversing the progress achieved in reducing cancer mortality over the past several decades,” the authors write.

Write to Jamie Ducharme at jamie.ducharme@time.com.

Read More From TIME

EDIT POST