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Your Good Health: The risk of colorectal cancer among young people is rising

Poor diet, lack of exercise and smoking are all plausible explanations , but obesity is one risk factor that is much more common now
Dr. Keith Roach

Dear Dr. Roach: I read in the paper that the rate of colorectal cancer has been rapidly rising since the 1990s among adults younger than 50. I also read that younger people are dying from the disease. Can you shed any light on why this is happening?


You are right. The risk of developing colon cancer at a young age is double for those born in the 1980s and 1990s compared with those born in the 1950s. Nobody knows exactly why this is, but there are some hypotheses.

Poor diet, lack of exercise and smoking are all plausible, but obesity is one risk factor that is much more common now. Toxins produced by the intestinal bacteria (called the microbiome) may have something to do with the increased incidence in younger people, since a poor diet promotes an unhealthy microbiome.

The most common symptoms and signs of colon cancer in younger people (by definition, those diagnosed with colon cancer before the age of 50) are similar to those found in middle-aged and older people: colonic bleeding (which can be bright red, dark or unable to be seen); abdominal pain; diarrhea; and iron- deficiency anemia. People of any age with these persistent symptoms should speak to their regular doctors, who can refer them for testing, if appropriate.

Because of the increased risk, the groups that make recommendations have emphasized that colon-cancer screening should begin at age 45, not 50 as it has been. While a colonoscopy is still considered to be the best screening test by most experts, other screening tests, such as stool-based DNA and immunochemical testing, are reasonable options. However, they must be followed up urgently with a colonoscopy if they prove to be positive.

Dear Dr. Roach: I am a 75-year-old man and had been seeing the same doctor for over 45 years. But he sold his practice, and the new doctor diagnosed me with pernicious anemia (PA) after my first blood test. My grandfather was born in Germany and the doctor thought that this was a contributing factor.

He prescribed B12 by injection. I have no family history of this anemia and wonder if it is necessary for me to continue this treatment.


PA is caused by an inability to absorb vitamin B12 efficiently. It’s most common in people with Northern European ancestry. Without vitamin B12, the body can’t make red blood cells (hence the “anemia”). It’s an autoimmune disorder in which the body destroys the cells that make a necessary cofactor for B12 absorption called “intrinsic factor,” which are the same cells that make acid in the stomach. This puts people with PA at risk of stomach cancer, so any stomach symptoms should prompt a thorough evaluation.

People with PA can sometimes have dangerously low B12 levels but don’t have anemia. Very low B12 levels can cause depression, difficulty thinking and sensation changes, since B12 is needed for proper nerve-cell function.

If your doctor was correct in his diagnosis, then you should be on vitamin B12 for life. Although many of my patients prefer the injection, a daily B12 tablet is just as effective.

A blood test with low B12 levels is not enough to make a diagnosis. A diagnosis can be confirmed by the presence of intrinsic factor antibodies or by the prompt resolution of symptoms and anemia (if present) with B12 treatment.

Readers may email questions to [email protected].