In Reply We appreciate the 2 valuable comments by Dr Mezuk and Dr Venniyoor that bring attention to the diverse and intertwined aspects of the rising incidence of obesity and early-onset colorectal cancer (CRC). Among US adults 20 years or older, obesity increased from 15% in 1980 to 40% in 2016.1,2 Therefore, obesity is clearly not ubiquitous. Moreover, it is unlikely that any amount of exposure to obesity is sufficient to produce disease; not every obese individual has CRC. As Dr Mezuk wrote, the fact that heavy smoking was not ubiquitous was what helped epidemiologists to determine the causal role of smoking in lung cancer. Likewise, obesity is not ubiquitous; a considerable increase in obesity began to emerge after 1980, about a decade before the rise of early-onset CRC, lending support to the possibility that obesity may be a contributor to the increase in early-onset CRC cases. It is worth noting that obesity-associated health consequences among a younger population may not be limited to CRC. With the exception of breast cancer, which is inversely associated with obesity among younger women,3 the incidence of several obesity-associated cancers such as multiple myeloma, uterine corpus, gallbladder, kidney, and pancreatic cancer are also on the rise among young adults.4
Liu P, Giovannucci EL, Cao Y. Becoming a Statistic in the Middle of an Epidemic—A Call to Consider Alternate Risk Factors for Early-Onset Colorectal Cancer—In Reply. JAMA Oncol. 2019;5(8):1228–1229. doi:10.1001/jamaoncol.2019.1329
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