A spate of stories has been published recently about the increased incidence of colonic cancer among younger Americans (see: Why Are More Young Americans Getting Colon Cancer?). I have been interested in the epidemiology of colonic cancer since I was a medical student when I was taught that cancer of the colon ws very common in Argentina and Scotland because of the high beef consumption (see: Review on meat consumption and cancer in South America). This was believed to alter the colonic bacteria flora which, in turn, produced carcinogenic chemicals in the gut. Many decades later, we continue to speculate about the epidemiology of colonic cancer. Below is an excerpt from this first article:
More than a decade ago, scientists noticed an odd quirk in the data: While overall rates of colorectal cancer have been falling dramatically since the mid-1980s, there's been a steady uptick of this disease among people younger than 50.....What's driving that is hard to say. Obesity is more common among younger than it used to be, so perhaps it's partly to blame. Or it may not be obesity itself; it could be that poor diet and lack of exercise, which contribute to obesity, are also influencing colon cancer rates....[A] professor of medicine at the Dartmouth Institute for Health Policy & Clinical Practice says what look like additional cancers in people under 50 may simply be cases that are being diagnosed earlier than they would have been....There's no question that diet and other factors can also have a profound effect on cancer rates....The increased screening for colorectal cancer has been a significant factor in reducing the burden of this illness.
Here is a short list of some of the theories used to explain why younger people may now be experiencing more colonic cancer:
- Obesity is increasing in this age group which then causes an increased cancer rate (see: Does body weight affect cancer risk?).
- Younger people are exercising les, leading to more cancer (see: Trim your cancer risk with exercise).
- The diet of younger people may be changing, which in turn alters the GI microbiome and predisposes to colonic cancer.
- Surveillance for colonic cancer is increasing, resulting in more colonoscopies and earlier detection and treatment of cancer. This results in an increased incidence of the disease but also reduced mortality.
The correct answer to the question presented in the caption of this note is that perhaps all of the above theories may be correct. Among them, what interests me most is the new research about the GI microbiome (see: Compositional and Functional Features of the Gastrointestinal Microbiome and Their Effects on Human Health). To conclude this note, here is a key quote from this article:
Beyond microbial richness and diversity, a healthy gut microbiome can be defined by the presence of classes of microbes that enhance metabolism, resilience to infection and inflammation, resistance to cancer or autoimmunity, endocrine signaling, and brain function (brain–gut axis). The microbiome may mediate these effects via secretion of factors that modulate intestinal permeability, the mucus layer, epithelial cell function, innate and adaptive immunity, intestinal motility, and neurotransmission