Several types of cancer are now more common among millennials and Generation X than in older generations, a new study suggests.
For the study, scientists examined data on more than 23.6 million American cancer patients born between 1920 and 1990 who were diagnosed with 34 different types of tumors. Overall, they found 17 cancers were more common among millennials and Generation X than older birth cohorts, according to findings published in Lancet Public Health.
For 8 of these 17 cancers, incidence rates have steadily climbed over time for each successive birth cohort since 1920. In particular, rates of several cancers were two to three times higher for the 1990 birth cohort than for people born in 1955. These include cancers of the small intestine, kidney, and pancreas in both males and females; and liver and bile duct cancer in females.
For the remaining nine cancers, incidence rates have been rising among younger generations after a decline in older adults, the study also found. These include cancers of the uterus, ovaries, testicles, colon, certain breast cancers, and cancers of the anus and blood and lymph vessel lining in men.
While it’s not clear exactly why many types of cancer are becoming more common among younger generations, obesity appears to play a role, says Hyuna Sung, PhD, the lead study author and a senior principal scientist at the American Cancer Society.
Obesity Has a Link to Cancer Risk
“Ten of the 17 cancers with increasing trend are associated with excess body weight,” Dr. Sung says. “Therefore, increased body weight could be one of the plausible factors. Other suspected risk factors include unhealthy diet, sedentary lifestyle, altered sleep patterns, and environmental chemical exposure during early life and young adulthood.”
Americans appear to be more at risk than people in Canada or Europe, and poor people in the United States appear to be most vulnerable, says Otis Brawley, MD, a professor of oncology and epidemiology at Johns Hopkins University in Baltimore who wasn’t involved in the new study.
“Diet — especially caloric intake — are the most likely culprits,” Dr. Brawley says. “Americans are getting heavier, obesity rates are increasing, ways of life are getting more sedentary. The obesity epidemic has not hit Europe or Canada as it has in the U.S.”
Compared with older individuals with the lowest cancer risk, the increased risk for people born in 1990 ranged from 12 percent higher for ovarian cancer to 169 percent greater for uterine cancer.
Mortality rates increased with each successive birth cohort for liver and bile duct cancers in females, as well as cancers of the uterus, gallbladder, testicles, and colon, the study also found. For other cancer types, however, mortality rates stabilized or declined in younger birth cohorts.
Demographic Shifts May Be Increasing Cancer Risk
Beyond rising obesity rates and lifestyle factors, the rise in some cancers may have to do with family planning, says Daniel Spratt, MD, a professor and the chair of radiation oncology at University Hospitals Seidman Cancer Center and Case Western Reserve University in Cleveland.
“Another contributing factor that may increase the risk of select cancers in biological females is women [now] have fewer children and have their first pregnancy later in life — and this trend has increased over time,” says Dr. Spratt, who wasn’t involved in the study. “There is a protective effect of various cancers with having children, such as breast and ovarian cancer, and the number of women who either have children later in life or do not have children has risen.”
It’s also possible that the rising cancer incidence is due at least in part to demographic shifts over time, with nonwhite people making up far more of the U.S. population in younger birth cohorts than they did a century ago, says David Chang, PhD, MPH, an associate professor of surgery at Harvard Medical School and the Mass General Research Institute in Boston, who wasn’t involved in the new study.
“What we were seeing in 1920 may really be disease trends among a Caucasian population, while now we are seeing disease trends that are more reflective of a mixed population,” says Dr. Chang, who wasn’t involved in the new study. “The Gen X and millennials are particularly diverse demographically.”
Beyond this, health disparities may also play a role in rising cancer rates among younger people, Chang adds. “If our data are now more inclusive and reflect more nonwhite patients, and nonwhite patients carry a higher disease burden, then these two factors may partially contribute to the higher disease trend that we are seeing,” Chang says.
If there’s good news in the study findings, it’s that many of the underlying risk factors that can make cancer more likely to develop are things that people can control. “At a personal level, I think patients can pay more attention to the harmful effects of obesity, unhealthy diet, sedentary lifestyle, and altered sleep patterns,” Chang says.
As always be Safe, Stay Healthy and be Careful out there
James A. Vito, D.M.D.