Bulk it up: High-fiber laxatives linked to lower colorectal cancer risk

But non-fiber types may actually boost risk of disease, Fred Hutch analysis finds
The kind of laxative you use may be associated with your risk of colon cancer, a new study suggests. Sebastian Kaulitzki / Shutterstock

When irregularity strikes, what do you do? If you’re like roughly 20 percent of Americans, you reach for a laxative to help ease symptoms of occasional constipation.

But a large new prospective study of more than 75,000 adults in western Washington finds that the type of laxative you take may influence your risk for colorectal cancer. Non-fiber stimulant laxatives like ex-lax, Correctol or milk of magnesia were associated with a nearly 50 percent higher risk of the disease, while high-fiber laxatives such as Metamucil, Citrucel or Fiberall appeared to cut the risk of colon cancer by more than half.  

That’s according to new work led by Jessica Citronberg, a pre-doctoral fellow in the epidemiology program of Fred Hutchinson Cancer Research Center’s Public Health Sciences Division. Her paper was published this week in the American Journal of Gastroenterology. 

“I was just surprised to see such a strong association between laxative use and colorectal cancer risk,” Citronberg said. “I didn’t expect the results to be as strong as they were.”

Co-authors included Dr. Elizabeth Kantor, Dr. John Potter and Dr. Emily White.

The study analyzed data from participant surveys in the large VITamins And Lifestyle Study, or VITAL, between 2000-2002 and 2008. It was aimed at clearing up conflicting reports about the effects of bowel movement frequency, constipation and laxative use on colorectal cancer risk. It’s the first study of its kind to look at the link between bulk fiber laxatives and cancer risk.

While the findings were robust, they’ll need to be replicated in future studies before any recommendations are issued about use of non-fiber stimulant laxatives vs. the high-fiber alternatives, Citronberg said.

“I wouldn’t necessarily jump the gun and say because of this study, people should stop taking stimulant laxatives,” she said. “I think the better route to go would just be to have a healthy diet.”

At the same time, the new study failed to find significant associations between bowel movement frequency or constipation and colon cancer risk, easing common worries. Researchers in the early 1970s had hypothesized that infrequent bowel movements raised the risk of colon cancer by increasing concentrations of cancer-causing substances in the stool and then keeping them in contact with the gut walls.

That would be a concern for the nearly 10 percent of people enrolled in the study who have fewer than five bowel movements a week, or the nearly 14 percent who go only five or six times a week. Nearly half of participants said they had bowel movements once a day and slightly more than 27 percent said they went twice a day.

Such detailed research into the intimate workings of human bowels is interesting to Citronberg, who said she’s always been drawn to the impact of nutrition and hopes to conduct more research into the gastrointestinal system and cancer risk.

If one in five Americans uses laxatives, it’s important to understand their potential impact, she said. Non-fiber laxatives – which are the most commonly used in the U.S. – work by forcing the colon to contract, while fiber-based laxatives increase water content and the bulk of the stool to move it through the colon.

“To me, I’ve always been interested in the public health risks,” said Citronberg, who is a doctoral student at the University of Washington. “What if there was an increased risk for laxative use?”

In the new study, people who used non-fiber laxatives more than five times a year had a 43 percent increased risk of colon cancer compared with those who used them less than once a year. In contrast, people who used fiber-based laxatives at least four days a week for four years had a 56 percent lower chance of getting the disease than those who didn’t use them.

That said, experts caution, don’t use them if you don’t need them.

Medical guidelines for treating constipation generally recommend non-drug treatments including increased dietary fiber, extra fluids and regular exercise, according to the journal American Family Physician. Laxatives should be used with care, advises the Mayo Clinic.

“Laxative use can be dangerous if constipation is caused by a serious condition, such as appendicitis or a bowel obstruction. If you frequently use laxatives for weeks or months, they can decrease your colon’s ability to contract – and actually worsen constipation,” the Mayo Clinic website advises.
Previous studies on laxative use have produced mixed results regarding the risk of colon cancer

The new study was large enough to account for confounding influences on colon cancer risk and it was a prospective study, so it allowed information on bowel habits and laxative use to be collected before any cancer diagnosis, reducing recall bias. But it was still based on self-reported responses and it didn’t include detail on stool consistency, which has been associated with higher colon cancer risk.

Because there are so many subtypes of laxatives, more research is needed to determine which kinds may be associated with higher cancer risk, Citronberg said.

“I think it’s definitely interesting in that it should be studied again,” she added.

Also in the news:

JoNel Aleccia is a former staff writer at Fred Hutchinson Cancer Research Center. From 2008 to 2014, she was a national health reporter for NBC News and msnbc.com. Before that she was a reporter, editor and columnist for more than two decades at newspapers in the Northwest. 

Solid tumors, such as those of the colon, are the focus of Solid Tumor Translational Research, a network comprised of Fred Hutchinson Cancer Research Center, UW Medicine and Seattle Cancer Care Alliance. STTR is bridging laboratory sciences and patient care to provide the most precise treatment options for patients with solid tumor cancers.

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