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NEW YORK (Reuters Health) - Long-term constipation doesn't raise risk for colon and rectal cancers according to a new analysis of the existing evidence.
Past studies had suggested a possible connection, but researchers said those results may have been skewed by poor study designs.
"Someone who's got chronic constipation is unlikely to be associated with colon cancer now or in the future," said study author Dr. Alexander Ford, senior lecturer at the St. James's University Hospital's Leeds Gastroenterology Institute in the UK.
Colorectal cancer is the second leading cause of cancer death in the U.S., with an estimated 51,000 Americans dying from it each year, according to the Centers for Disease Control and Prevention.
Established risk factors for the disease include a personal or family history of colorectal cancer, irritable bowel disease, certain syndromes that cause colon polyps, type 2 diabetes, obesity, heavy drinking, smoking and being over age 50, according to the American Cancer Society.
Some experts have hypothesized that chronic constipation, by causing prolonged contact between potentially carcinogenic substances in the stool and the lining of the colon, might also increase the risk of cancer.
Studies in recent decades have both supported and refuted that idea, so Ford and his colleagues reanalyzed data across 28 studies that examined the connection between constipation and colorectal cancer. In total, the data included over 250,000 participants from 1966 to 2011.
Ford's team found little support for a link between constipation and cancer risk, according to their findings published in the journal Gastroenterology.
Studies that showed an association typically included questionnaires for participants to recall bouts of constipation. Ford told Reuters Health those studies suffered from bias because the suggestion of constipation could lead people to misremember their symptoms.
However, in stronger studies that tracked people for both constipation and colorectal cancer over six to 12 years, the researchers found no connection.
"If they just have constipation in isolation then that does not seem to be a risk factor for colon cancer," said Ford, who received funding from Allmiral, makers of Linaclotide, a drug currently under testing for irritable bowel syndrome. The Spanish pharmaceutical company was not involved in the study's design or execution.
Symptoms of advanced colon cancer typically include diarrhea or looser stools, unintentional rapid weight loss, abdominal pain, anemia and rectal bleeding.
Ford's team also found that studies focused just on colorectal cancer patients did find a significantly higher rate of constipation in patients compared to people without colorectal cancer, but again, those studies had weaknesses.
"The primary message should really be that colorectal cancer in its early stages usually has no symptoms at all," said Dr. Durado Brooks, director of prostate and colorectal cancer for the American Cancer Society, who was not involved in the current study.
"It's important to talk to your doctor about screening tests before any symptoms develop," Brooks told Reuters Health.
For doctors and patients alike, chronic constipation - typically defined as three or fewer bowel movements per week over the course of three months - can seem like an early warning sign for colon cancer, according to Ford.
For many constipated patients, a visit to the doctor often leads to colonoscopy, an invasive visual test that checks for cancer polyps on the colon and rectal wall.
"In my own clinical practice, we still regularly get referrals for colonoscopies if the patient simply has constipation," Ford said.
Colorectal cancer detection guidelines don't include constipation as an alarming sign, and based on the results of the new study, Ford thinks that doctors should not refer patients with constipation for colonoscopy to rule out cancer.
His team's analysis found that when patients were sent for colonoscopy with constipation as the primary reason, their rates of colon cancer were in fact lower than average.
To screen for colorectal cancer, experts advise that anyone over 50 should receive an annual test to detect blood in the stool and a colonoscopy every 10 years. Those with family histories of colon cancer should be tested more frequently and at a younger age.
Though constipation may not be a risk factor for colon cancer, the issue shouldn't be ignored, researchers said.
"Managing chronic constipation, is done through diet, additional fiber, even some exercise can help," said Dr. Seth Gross, assistant gastroenterology professor, at New York University's Langone Medical Center. Gross was not involved in the current study.
"There are even medications available that could help someone go on a more regular basis. Even though it's not the perfect paper, the study gives us reassurance." Gross told Reuters Health.
SOURCE: bit.ly/YIPWuj The American Journal of Gastroenterology, online March 12, 2013.