As Americans get heavier, obesity-linked cancers may strike earlier

Increasing numbers of middle-aged Americans appear to be developing cancers that can be associated with obesity, new data suggest.

And the increase in these cancers among 50- to 64-year-olds parallels the rising rates of obesity, researchers say.

In their analysis of more than six million cancer cases, researchers found that obesity-associated cancers appeared to be shifting to younger people, including those under 50, according to the report published in JAMA Network Open.

“Obesity creates a state of constant low-grade inflammation, as well as multiple growth stimulating factors, all of which can accelerate the development of cancer,” explained the study’s lead author, Siran Koroukian, an associate professor in the department of population and quantitative Health Sciences at the Case Western Reserve University School of Medicine and director of the Population Cancer Analytics Shared Resource at Case Comprehensive Cancer Center, both in Cleveland, Ohio.

It’s possible that people can impact their cancer risk by watching their weight, Koroukian said in an email. “There is some evidence that weight loss (among those who are obese) can prevent the development of cancer,” she added. “The most important strategy is maintaining a normal weight.”

To take a closer look at the impact of obesity on cancer risk, Koroukian and her colleagues turned to data from the Surveillance, Epidemiology and End Results 18 (SEER18) database, focusing on cancer cases diagnosed from 2000 through 2016. The database is nationally representative and covers geographically diverse regions of the country.

The researchers looked for trends in the percentage of cases diagnosed in three age groups: 20-49, 50-64 and 65 and older.

Obesity-associated cancers considered by the researchers included myeloma, female breast cancer and cancers of the colon and rectum, gallbladder, esophagus, stomach, liver, pancreas, uterus, kidney and thyroid.

Among the more than 6 million cases, 43.6% were obesity-associated cancers.

When the researchers analyzed their data, they found a greater increase in the odds for an obesity-associated cancer compared to non-obesity associated cancers in the 50- to 64-year age group, but a decrease for older individuals.

While it looks like the growing rates of obesity are driving up obesity-associated cancers, this study can’t prove that, said Dr. Daniel Labow, chair of surgical oncology at the Mount Sinai Health System.

A major limitation of the study, he pointed out, is that the SEER database does not include information on body mass index, so it’s impossible to know whether these cancers are actually occurring in obese individuals.

“There are so many other factors that could be affecting trends and movements in cancer incidence,” Labow said. For example, the trend could be explained by the kinds of foods people are eating, he added.

“A high animal fat diet and lots of processed foods certainly could be contributing,” Labow said. Nevertheless, “obesity is not good for many different things so we should be working on decreasing it and it would be nice if we also saw a downstream trend of reduction of cancers,” he added.

Dr. Jian-Min Yuan agrees that there could be many factors that changed over time besides obesity. “A person who was a teen in the late 70s to early 80s, might have experienced a lifestyle change,” Yuan said. “Maybe they were more stressed. Maybe they ate a lot more meat and consumed less fiber. They could have consumed more alcohol. Their sleeping patterns might have changed in that era because of a much faster modern lifestyle.”

SOURCE: JAMA Network Open, online August 14, 2019.