Millennials are facing a much higher risk of obesity-related cancers than baby boomers did at their age, according to a study published in The Lancet Public Health Monday.

Why it matters: The steepest increases for obesity-related cancers were in the youngest age group (aged 25–34 years) and are a warning that steps need to be taken by this generation to get rid of excess body weight. "The change in cancer trends among young adults is often considered as a bellwether for future disease burden," study author Hyuna Sung tells Axios.

Background: While scientists are not sure of the exact mechanism, there is "quite convincing evidence" that excess body weight increases the risks of some cancers, says Sung, principal scientist of surveillance research at the American Cancer Society (ACS).

Some theories behind this correlation are that excess body weight can affect inflammation and hormones, or that it's impacting the gut's microbiome.

What they did: Using a population-based cancer registry, researchers from ACS and the National Cancer Institute examined invasive cancers in people aged 25–84 diagnosed between 1995–2014 for 30 cancers, including 12 obesity-related ones.

What they found: Multiple obesity-related cancers increased significantly faster among the young adults (25–49 years) compared to older adults (50–84 years). "Indeed, the younger, the faster," Sung says.

6 of the 12 obesity-related cancers — colorectal, uterine corpus (endometrial), gallbladder, kidney, multiple myeloma and pancreatic — showed increased incidences in young adults and in successively younger birth groups in a stepwise manner.

The risk of colorectal, uterine corpus, pancreatic and gallbladder cancers in millennials is about double the rate baby boomers had at the same age, per the report.

But, for almost all (16 out of 18) of the non-obesity related cancers (exception was gastric non-cardia cancer and leukemia), cancers dropped or stabilized in successively younger generations — meaning the absolute risk of all cancers is lower for the youngest age groups. This included cancers related to HIV infections or smoking.

Why? Sung says while there are multiple factors involved, the obesity epidemic is happening because...

"[The] food environment we are living in promotes over-consumption of energy-dense, high-sugar/nutrient-poor foods that are pervasive and much more affordable and available to all."

"Furthermore, physical activity has been 'engineered' out of [our] lifestyle due to energy saving technologies, such as via the use of cars instead of bicycles."

What's next: Three main steps need to be taken, Sung says.

People need to adopt healthy lifestyles at younger ages. "Early lifetime exposure matters," she says. Physicians need to increase obesity screening and counseling. "Less than half of primary care physicians regularly assess for body mass index despite national screening recommendation," Sung says. Policymakers should broadly implement regulatory interventions like "restrictions on advertising calorie-dense food and drinks, taxes on sugary drinks, [and] urban planning ... to promote physical activity" through more sidewalks and bike lanes, Sung adds.

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Editor’s note: The chart was corrected to show year-on-year percent increase from 1995 to 2014 (not percent increase over the time period).