"The findings from this study are a warning for increased burden of obesity-related cancer in older adults in the future, potentially halting or reversing the progress achieved in reducing cancer mortality over the past several decades".
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.
Patients were divided into five-year age groups from 25-29 to 80-84 years old. The researchers believe that the increase is tied to the prevalence of obesity in the country and among young people.
But, for nearly all (16 out of 18) of the non-obesity related cancers (exception was gastric non-cardia cancer and leukaemia), cancers dropped or stabilized in successively younger generations - meaning the absolute risk of all cancers is lower for the youngest age groups.
"Yet, I think the public in general doesn't even know that obesity is associated with cancer", said Case Western Reserve University oncologist Dr. Nathan Berger, who was not associated with the American Cancer Society study.More news: Dolphins officially announce Brian Flores as new head coach
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In addition, millennials (anyone born between 1981 and 1996) these days are twice more likely to develop colorectal, endometrial, pancreatic and gallbladder cancers than baby boomers (people born worldwide between 1946 and 1964) when they were the same age.
Researchers from the American Cancer Society studied cancer data covering half of the United States population between 1995 and 2014. On the bright side, the study also found that the cancers linked to smoking and infections have decreased among the youth. For incidence rate ratios please see Tables S5 (12 obesity-related cancers) and S6 (18 additional cancers) in the appendix.
"The lesson we've learned from other cancers is if steps aren't taken to stop the things causing those trends, then they will continue to get higher", Schwartz says.
The authors of the study argue that further research is needed to determine what factors are driving the trend. These changes include genetic flags and markers - epigenetic modifications - that increase cancer risk and may remain long after weight loss.
"We need to make the public aware that there's no time that it's OK to be obese", Berger said.
"But in the future, obesity could reverse that progress", co-author Jemal cautioned.