Millennials Are Getting More Obesity-related Cancers As Excess Body Weight Takes Its Toll on a Generation

File photo: The incidence of six obesity-related cancers is rising faster in young Americans than in older generations, according to a new study. iStock

Over the past few decades, scientists have uncovered an increasing body of evidence linking obesity to the development of certain cancer types.

Now, researchers have found that the risk of developing six of these obesity-related cancers has increased for young American adults in comparison to older generations, according to a study published in The Lancet: Public Health.

A team from the American Cancer Society, led by Hyuna Sung, examined incidence trends in the United States for 30 common cancers—12 of which have previously been associated with obesity.

Using the "Cancer In North America" database, they collected information on these 30 types in patients aged 25-84 who were diagnosed between January 1, 1995, and December 31, 2014. The data was taken from 25 state registries, covering 67 percent of the U.S. population.

The researchers then estimated the change in incidence rates for each of the cancers within five-year age groups, beginning with 25-29 and ending with 80-84.

Overall, they documented 14,672,409 cases of these 30 cancers between 1995 and 2014, finding that the incidence of six of the 12 obesity-related types (colorectal, uterine corpus, gallbladder, kidney, pancreatic and a type of blood cancer known as multiple myeloma) rose significantly in adults between the ages of 25 and 49.

While the incidences of these cancers also rose in older adults—with the exception of colorectal—the data showed steeper increases in successively younger ages.

For example, the incidence of pancreatic cancer among those aged 45-49 increased by 0.77 percent compared to a rise of 2.47 percent for ages 30-34 and 4.34 percent for the group aged 25-29.

"Similarly, the annual percent change by age was largest in individuals aged 25–29 years for cancers of the kidney, gallbladder, corpus uteri, and colorectum, and in individuals aged 30–34 years for multiple myeloma," the authors wrote in the study.

In fact, for colorectal, uterine corpus, pancreas and gall bladder cancers, the incidence rate among millennials was about double the rate of baby boomers when they were the same age.

The picture is very different when looking at the 18 other non-obesity-related cancer types: Incidence increased in successively younger generations for only two of these, while it decreased in about half of them (particularly those related to smoking or HIV infection.)

According to the researchers, the growing obesity epidemic in the United States could be influencing the trends identified in the study. They cite figures which show that the prevalence of obesity or being overweight increased by more than 100 percent (from 14.7 percent to 33.4 percent) between 1980 and 2014 among U.S. children and adolescents. Furthermore, it rose by 60 percent among adults aged 20–74 years (from 48.5 percent to 78.2 percent.)

Ahmedin Jemal, a senior author of the paper, told Newsweek that obesity is thought to cause cancer by "increasing the rate of damages to genes (mutations) and by promoting the growth (multiplications) of abnormal cells or tumors."

He noted that although the absolute risk of these cancers is small in younger adults, the new findings have important public health implications.

"The implication of this finding is that unless we take measures to reverse the obesity epidemic in young adults, the burden of obesity-related cancer in older adults will increase in the future," he said. "This may halt or reverse the progress made in reducing the cancer mortality rate over the past 2-3 decades."

This article was updated to include comments from Ahmedin Jemal.