Study Authors Speculative About Causal Relationship
February 04, 2019
In the United States from 1995 to 2014, the incidence of six of 12 obesity-related malignancies increased among "young" adults (25-49 years), according to a new observational study.
However, the incidences for these cancers — except for colorectal cancer —also rose in older adults (50 years or older), acknowledge the authors, led by Hyuna Sung, PhD, cancer epidemiologist and principal scientist, Surveillance and Health Services Research Program at the American Cancer Society. The study was published online today in The Lancet Public Health.
But the young adults, who were the focus of the study, had larger annual percentage increases than the older adults.
On the other hand, the six obesity-related cancers that did not increase in young people were breast, esophageal, gastric cardia, liver and intrahepatic bile duct, thyroid, and ovarian.
Despite the findings, the study is not evidence of a causal relationship between obesity and cancer.
Furthermore, an expert not involved with the study questioned the concept of "obesity-related" cancers.
"The obesity–cancer story is far from clear and while the authors selected cancers that might be obesity related, they also might be related to other factors not considered that may be changing over time but that were not examined," Ruth Etzioni, PhD, a biostatistician at Fred Hutchinson Cancer Research Center in Seattle, told Medscape Medical News.
"I worry about inflammatory articles like this one misinforming the public," she added.
Nevertheless, senior author Ahmedin Jemal, DVM, PhD, vice president of the Surveillance and Health Services Research Program at the American Cancer Society, sounded an alarm about the results.
"Our findings expose a recent change that could serve as a warning of an increased burden of obesity-related cancers to come in older adults," he said in a press statement. "Most cancers occur in older adults, which means that as the young people in our study age, the burden of obesity-related cancer cases and deaths are likely to increase even more."
Jemal and coauthors called for increased obesity screening in young adults.
In an accompanying editorial, Catherine Marinac, PhD, and Brenda Birmann, ScD, of Harvard University in Boston, Massachusetts, say that it is "plausible" as well as "provocative" that obesity is driving the reported results. But, they add, the investigators' interpretation of that relationship is "speculative."
Furthermore, the editorialists write that they would have liked to have heard the study authors' thoughts about why only some obesity-related cancers were on the rise in young adults — and not all 12.
Both sets of experts call for further research to uncover the exposures responsible for these "emerging trends."
Eighteen Other Cancers Examined
Notably, the study authors also report that, among the six cancers on the rise in the young adults, there was a steeper increase in progressively younger ages (P wald > .05).
For example, over the study period, the average annual change for pancreatic cancer was equal or less than 1% in people ages 40 to 84, 1.3% in those ages 35 to 39, and 2.5% in 30 to 34-year-olds. In the youngest age group (ages 25-29), it was 4.3%.
The investigators did not look at solely obesity-related cancers.
The researchers also reviewed incidence data on 18 other (non–obesity-related) cancers. And the findings were telling, they suggested: "…the incidence increased in successive younger generations for only two of the 18 additional cancers, and decreased for about half of the remaining cancer types."
In their study discussion section, the authors comment extensively about obesity in the United States and suggest their new findings may be related to recent trends showing increases in body weight.
"These [cancer incidence] trends might have been influenced by the rapid rise in overweight or obesity prevalence in the USA. Between 1980 and 2014, overweight or obesity prevalence in the USA increased by more than 100% (from 14.7% to 33.4%) among children and adolescents and by 60% among adults aged 20-74 years (from 48.5% to 78.2%)," they write.
Lead author Sung commented at length about food quality as a possible contributor to the newly found trends: "Obesity is associated with health conditions that can contribute to the risk of cancer. For example, diabetes, gallstones, inflammatory bowel disease, and poor diet can all increase the burden of cancer," she said. "The quality of the American diet also has worsened in recent decades. More than half of adults who were 20 to 49 years old between 2010 to 2012 reported poor dietary habits, such as eating little fruits, vegetables, whole grains, fish, and shellfish at the same time as eating too much salt, fast food, and sugary drinks."
The study was funded by the American Cancer Society and the National Cancer Institute. The study authors, editorialists, and Etzioni have disclosed no relevant financial relationships.
Lancet Public Health. Published online February 4, 2019.
Source: Six 'Obesity-Related' Cancers on Rise in US Young Adults - Medscape - Feb 04, 2019.