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Early-onset colorectal cancer (CRC) saw the most rapid increases among white adults in Western states -- a surprising phenomenon since these areas are generally known for their pursuit of healthier lifestyles, researchers found.

CRC incidence among adults ages 20-49 increased in 40 out of 47 states among non-Hispanic white adults, reported Rebecca L. Siegel, MPH, of the American Cancer Society in Atlanta, and colleagues.

In fact, 10 states had at least a 2.6% average annual percentage change in the rates of colorectal cancer -- six of which were in the western U.S., the authors wrote in the .

has found that while U.S. colorectal cancer rates are declining overall, they are increasing in young adults. Established CRC include obesity, a high intake of red and processed meat, low fiber consumption, physical inactivity, smoking, and excess alcohol use. has linked early-onset colorectal cancer risk in women to a sedentary lifestyle, using the proxy of prolonged daily TV watching.

"This is a very interesting analysis of the rate of change in young-onset CRC across different states," Dennis J. Ahnen, MD, of the University of Colorado Hospital in Aurora, told 口袋女优.

Ahnen, who was not involved in this research, said the findings offer "new information that might suggest hypotheses about the cause of the alarming increase in early-onset colorectal cancer. The general pattern is counterintuitive in that the largest increases tended to be in the Western states that tend to have the lowest overall rates of CRC and these states, interestingly, still tend to have the the lowest overall rates of early-onset CRC."

Siegel said that many exposures outside of known risk factors are being discussed as potential causes. "These include alterations in the gut microbiome because of changes in diet such as increased intake of highly processed foods and high glycemic load carbohydrates, the rapid increase in antibiotic use, and food additives, including high fructose corn syrup and emulsifiers," she told 口袋女优.

suggests that non-nutritive sweeteners may also adversely impact the gut microflora, exerting a bacteriostatic effect. As for a possible climate effect in the sunny West, the evidence remains inconclusive about the relationship between vitamin D and CRC, but leans toward a protective effect, Siegel added.

Study Details

Researchers examined more than 240,000 cases of invasive colorectal cancer from the and national survey data from the (BRFSS), representing 95% of the U.S. population.

From 2006 to 2015, overall incidence of colorectal cancer rose by 1.1% annually from 2006 to 2015, with increases in 36 of 47 states. Rates rose faster for rectal tumors at 1.7% per year than for colon tumors at 0.7% per year.

Examining colorectal cancer incidence by state, the authors found that incidence increased in Washington during the study period from 6.7 per 100,000 to 11.5 per 100,000 (RR 1.73, 95% CI 1.48-2.01), and from 6.0 to 9.5 in Colorado (RR 1.57, 95% CI 1.30-1.91). Despite these increases, researchers wrote that colorectal cancer incidence rates were "generally lowest in Western states" from 2011-2015, and current CRC incidence remained highest in Southern states.

The authors noted colorectal cancer incidence increased in young white adults in "more than four-out-of-five" states, though it was mostly stable among black and Hispanic adults. Early-onset CRC incidence among blacks was stable in 21 of 27 states, and upward trends were confined to rectal cancer, the authors noted.

While lower baseline rates in western states may have contributed to these relatively rapid increases, the authors explained, the average annual percent change for rectal cancer in Kentucky, where colorectal cancer incidence was highest, was 2.8% (95% CI 2.0-3.6) -- the same as that in Washington.

By cancer subtype, the current study found generally steeper increases for rectal than for colon malignancies, with rates doubling in some states. In Colorado, for example, the rectal cancer rate rose from 1.9 to 4.2, aligning with rates for colon cancer.

'Usual Suspects' Ruled Out?

From 1995 to 2005, all states saw increases in obesity prevalence in adults ages 20-49, with the greatest absolute changes in the South, where prevalence was highest, the authors said. A third of states saw increases in heavy alcohol consumption, but neither of these factors correlated with CRC incidence trends.

"The prevalence of smoking and heavy alcohol use among young adults is low and trends do not appear to explain the CRC incidence trajectory, the authors wrote, calling for studies to explore novel risk factors for CRC in young adults," they wrote.

"Although early-onset colorectal cancer incidence is ... consistent with the prevalence of established risk factors, like obesity, physical inactivity, and smoking, this pattern may change because the steepest increases are in Western states," Siegel said in a news release. "This finding suggests that early life exposures in addition to the 'usual suspects' may be contributing to the rise in early onset disease."

Ahnen also cited the possibility of unknown risk factors being responsible for some of the increase. "This is a hypothesis worth testing," he said.

Among the study's limitations, Siegel and colleagues noted that changes in tumor site coding by clinicians may have contributed to increased rectal cancer rates. Additional limitations included potential biases in self-reported health information from BRFSS surveys, as well as the absence of state-level colonoscopy data for adults younger than age 50, which may have contributed to variations in trends.

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