Millennials have about double the risk of some cancers compared to Baby Boomers at same age.

An American Cancer Society-led study finds rates are increasing for 6 of 12 cancers related to obesity in younger adults in the US, with steeper increases in progressively younger ages and successively younger generations. The study, appearing in The Lancet Public Health, also looked at rates for 18 cancers unrelated to obesity and found rates increasing for only two.

The obesity epidemic over the past 40 years has led to younger generations experiencing an earlier and longer-lasting exposure to excess adiposity over their lifetime than previous generations. Excess body weight is a known carcinogen, associated with more than a dozen cancers and suspected in several more. Exposures to carcinogens during early life may have an even more important influence on cancer risk by acting during crucial developmental periods.

Several years ago, the authors of the current study identified increases in early onset colorectal cancer in the US, a trend that has been observed in several high-income countries and could partly reflect the obesity epidemic. For the new study, they extended that analysis by examining recent age-specific trends in 30 types of cancers, including 12 known to be associated with obesity.

Investigators led by Hyuna Sung, PhD, analyzed 20 years of incidence data (1995–2014) for 30 cancers in 25 states from the Cancer in North America database provided by the North American Association of Central Cancer Registries, covering 67% of the population of the US. The authors say theirs is the first to examine systematically the incidence trends for obesity-related cancers in young adults in the US.

Incidence increased for 6 of the 12 obesity-related cancers (colorectal, uterine corpus [endometrial], gallbladder, kidney, pancreatic, and multiple myeloma) in young adults and in successively younger birth cohorts in a stepwise manner. For example, the risk of colorectal, uterine corpus, [endometrial], pancreatic, and gall bladder cancers in millennials is about double the rate baby boomers had at the same age. In contrast, rates in successive younger birth cohorts declined or stabilized in all but 2 of 18 non-obesity related cancers, including smoking-related and infection-related cancers.

“Although the absolute risk of these cancers is small in younger adults, these findings have important public health implications,” said Ahmedin Jemal, DVM/PhD, scientific vice president of surveillance & health services research and senior/corresponding author of the paper. “Given the large increase in the prevalence of overweight and obesity among young people and increasing risks of obesity-related cancers in contemporary birth cohorts, the future burden of these cancers could worsen as younger cohorts age, potentially halting or reversing the progress achieved in reducing cancer mortality over the past several decades. Cancer trends in young adults often serve as a sentinel for the future disease burden in older adults, among whom most cancer occurs.”

The authors say innovative strategies are needed to mitigate morbidity and premature mortality associated with obesity-related diseases, primarily by health-care providers and policy makers.