Fewer people in the U.S. are getting colorectal cancer (CRC), but that progress is seen much more often in well-off and highly educated Americans. In fact, the gap is widening in rate of colorectal deaths in people with less education and/or who live in deeply disadvantaged communities.

Researchers now have shown that differences in weight, diet and physical activity play a huge role in the higher rates and deaths from CRC among people of lower socioeconomic status.

In a paper published in the Sept. 4 2012 Journal of the National Cancer Institutea careful statistical analysis of  a 10-year observational study of a half-million people indicated that helping people of lower education or income to change their diet, body weight, smoking and physical activity could be nearly as important as improved screening for reducing CRC deaths.In the past 10 years, rates of colorectal cancer have dropped 2 to 3% each year. Half of that decrease, researchers say , can be explained by changed behaviors—such as eating less red meat and increasing exercise. The other half is probably due to improved screening which detects CRC before it starts or advances.  

But that decrease in CRC is seen disproportionately more often among more educated and affluent Americans. In this week’s JCNI , Dr. Chyke Doubeni and colleagues at the University of Pennsylvania’s Dept. of Family Medicine and Community Health analyzed data to quantify how much “modifiable” health behaviors like exercise and diet might be responsible for higher rates of CRC among less educated and lower-income people.

Older couple eating togetherDoubeni used data from the NIH-AARP Diet and Health Study, which followed 506,000 middle-aged and elderly men and women over 10 years (1995-2006), to study the 7,676 study participants who developed colorectal cancer. After adjusting for age, sex, race, CRC family history, and state of residence, the authors analyzed how physical activity, smoking, diet, and body weight contributed statistically to different risks and locations of colorectal cancer in people according to their education level and socioeconomic status.

The study revealed that

(1)   CRC incidence rates were 42% higher among the least educated , and 31% higher among those living in the most disadvantaged neighborhoods, compared to better educated adults in higher-income neighborhoods;

(2)   The diagnosis gap between socioeconomic groups was much greater for distal (left) colon and rectal cancers (which are easier to detect than right-colon cancers by screening);

(3)    Overall, the combination of health behaviors and body mass index (BMI) explained about 44% of association between education and CRC risk; and 36% of the association between socioeconomic status of the subjects’ neighborhood and CRC risk.

Although this is the largest prospective study yet done, the authors cautioned that it is an “observational” study that doesn’t establish cause. In an accompanying editorial, Dr. John Ayanian of Harvard Medical School discussed possible biological explanations, such as:

(a)    Higher ingestion of charred red meat and lower vitamin D intake, plus higher bile acids in the proximal colon, affect the colon’s bacteria and “microbiome;”

(b)    Lower physical activity and obesity are linked with higher insulin levels that might stimulate the Wnt signaling pathway to stimulate cancer formation.

Dr. Ayanian called for public health authorities to consider using screening colonoscopies which detect proximal and flat lesions better than other screening methods; “chemoprevention through the use of aspirin” or NSAIDs; and targeted efforts to improve diet and exercise among people living in disadvantaged communities.

Sources: advance access Sept. 5 2012, Journal of the National Cancer Institute (doi: 10.1093/jnci/djs346); and Medscape Oncology News Sept. 5 (http://www.medscape.com/viewarticle/770355).

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