One study found that people from Africa who were suddenly switched to an American diet had signs of inflammation in their colons within just two weeks, Siegel notes, “so this change can happen fairly rapidly.”
But that’s far from a complete explanation. A large British study published a few years ago suggested that only 11 percent of colon cancer cases could be tied to trends in obesity.
There’s also a scenario in which this seemingly glum cancer trend is in fact good news.
Dr. H. Gilbert Welch, 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. Some people are getting colonoscopies for reasons other than cancer screening these days, and doctors are surely coming upon early cases of colon cancer they might not have turned up so soon.
There’s some evidence to back that claim: While the rate of new cases of colorectal cancer has been climbing in under-50 Americans since the mid-1990s, the death rate among that group has remained remarkably flat. And death rates may be the more telling statistic.
Something similar happened with breast cancer in the 1980s — there was a temporary spike in the number of breast cancers diagnosed, as large numbers of women went in for mammography screening for the first time. But death rates didn’t rise, and incidence rates of breast cancers fell again after that uptick.
Welch notes that we’re seeing that again with the rates of thyroid cancer, which are skyrocketing due to intensive screening and diagnosis; but, again, there’s been no increase in mortality from thyroid tumors.
Welch offers yet another possibility: Maybe the apparent rise in colon cancer among young people is real, but it won’t affect them as they age. “The biology of the disease may be different between the young and the old,” he says.
Welch himself has explored the much larger trend of declining colorectal cancer rates. Some of it is no doubt caused by vastly increased screening for colorectal cancer, though he notes that the decline was well under way before colonoscopies became routine.
There’s no question that diet and other factors can also have a profound effect on cancer rates. “One of the most dramatic cases of that is stomach cancer, which used to be a very common cause of cancer and has now virtually disappeared, at least in the United States,” Welch tells Shots.
On one point there is broad agreement among doctors and researchers treating and studying this disease: The increased screening for colorectal cancer, which can involve removing polyps before they become cancer, has been a significant factor in reducing the burden of this illness.
Another point of agreement: If the Trump administration eliminates the current insurance benefit for colon cancer screening as it does away with the Affordable Care Act, fewer people are likely to get screened for this deadly malignancy. And the likely impact of that is not a mystery.
You can contact Richard Harris at rharris@npr.org.
Article Appeared @http://www.npr.org/sections/health-shots/2017/02/28/517563769/why-are-more-young-americans-getting-colon-cancer