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Mirroring the decades-long increase in obesity rates in the U.S., cancers that are thought to be driven at least in part by excess weight are also on the rise among people under age 50, a new study suggests.
Rates for six of 12 cancers related to obesity have been increasing in successive generations of young adults, with the sharpest increases in the youngest age groups, researchers reported Sunday in The Lancet Public Health.
The new study may serve as a warning that if the obesity epidemic continues, there will be an explosion of these fat-sensitive cancers in the years to come, said the study's senior author, Dr. Ahmedin Jemal, scientific vice president of surveillance and health services research at the American Cancer Society.
"This finding signals an increased burden of obesity-related cancers in older adults in the future and calls for actions to mitigate this burden," he said in an email.
The researchers analyzed data from a central database of state cancer registries, focusing on new diagnoses of 30 types of cancer, 12 of which are associated with excess weight, from 1995 to 2014. They had complete data from 25 states that represent about two-thirds of the U.S. population.
In that 20-year period, there were about 14.7 million new cases of the 30 cancers. For at least eight cancers, including smoking-related and HIV-associated cancers, the incidence rates dropped.
But for six of the 12 obesity-related cancers — colorectal, endometrial, gallbladder, kidney, pancreas and multiple myeloma — there was a steady increase in incidence over the years, with larger increases in younger adults.
The annual rise in new cases of kidney cancer, for example, was 6.23 percent among people aged 25-29, but about 3 percent in the 45-49 age group. Similarly, pancreatic cancer incidence rose 4.3 percent each year for 25- to 29-year-olds but less than 1 percent annually among people aged 45-49.
Overall, rates of colorectal, endometrial, pancreatic and gallbladder cancers in millennials — young adults born around 1985 — were about double the rates seen in people born in the 1950s at the same age, the researchers note.
Especially striking was the rising rate of kidney cancers. Millennials were nearly five times as likely as baby boomers to develop cancer of the kidneys.
In contrast, for all but two of the 18 cancers not related to obesity, rates either stabilized or declined in successive younger birth cohorts.
Jemal said he hopes that the new findings will sound an alarm for doctors treating young adults. "Less than half of primary care physicians regularly assess body mass index despite national screening recommendations," he said. "Further, only a third of patients report receiving a diagnosis or weight loss counseling."
Public health measures, such as restrictions on advertising of unhealthy calorie-laden foods, could also help, as well as more campaigns to promote healthy lifestyle choices, Jemal said.
The cancer-obesity issue "is a really important topic because we've had an obesity crisis now for a number of decades," said John Jakicic, a professor and director of the Healthy Lifestyle Institute at the University of Pittsburgh in Pennsylvania. "At some point we started to see that diabetes was tracking with obesity. What we're seeing now is something similar with respect to certain cancers."
Cancer prevention will most likely involve "prevention of other things that might precipitate cancer," said Jakicic, who wasn't involved in the study. And while researchers don't yet know exactly how obesity may be driving up cancer rates, it's "critically important" to see observational studies that show an association between the two, he noted.