Colon cancer grows slowly, so the medical recommendation is that people with average risk factors have a colonoscopy screening test only every 10 years after age 50. With a family history of intestinal problems and colon cancer, I was told to have a colonoscopy every five years. After my last colonoscopy, my gastroenterologist told me that she removed a non-cancerous polyp and that I had a dark colon, a condition called “melanosis coli.”
What is melanosis coli?
Melanosis coli is the deposition of dark pigment in the lining layers of the colon. The dark color may be uniform or stippled. Tissue analysis shows that immune cells, called macrophages, contain the dark pigment. A major cause of melanosis coli is the use of herbal laxatives such as senna. Senna and other herbal laxatives contain chemical compounds, called anthraquinones. Macrophages are scavenger type immune cells that digest dead cells and cell debris. The dark discoloration is thought to arise from anthraquinone colored metabolites or by ingested cell debris from anthraquinone-induced colon cell death. Normally, colon lining cell turnover occurs every few days – it is one of the most rapidly renewing organ linings.
Is melanosis coli a precancerous condition?
Pat studies found that rats given high doses of herbal laxatives formed abnormal colon crypts or developed precancerous lesions, while other studies showed none of these effects. Extensive recent human studies found no association between melanosis coli and precancerous conditions or colon cancer. A study looking at potential nerve damage also found no association with anthraquinone herbal laxative use. Although many physicians believe that the dark colon represents anthraquinone laxative staining by anthraquinone residues, others caution against continuous use because of potential damage to the colon wall in susceptible individuals. Studies show that the colon returns to normal when anthraquinone laxatives are stopped.
Anthraquinone herbal laxatives
Senna, an extract of senna leaves and pods, is probably the most commonly used anthraquinone herbal laxative, but anthraquinone laxatives also include aloe, buckthorn (frangula), rhubarb root and cascara sagrada. I have been taking an herbal prep that came highly recommended by a friend for about a year. This herbal prep contains aloe, cascara and senna. Anthraquinones are degraded in the colon into more active compounds, which act directly on the intestinal wall. Anthraquinone laxatives are stimulant laxatives that are gentler than many other stimulant chemical laxatives.
For many people, a diet rich in fiber, plenty of water or other liquids and daily physical activity ensure a good functioning digestive system. But for some people, whether it is due to genetics, medications, hormonal conditions or the aging process, such a diet and exercise are not enough. Laxatives containing bulking agents, such as polyethylene glycol and fiber, or stool softeners do not work well for these people – they need stimulant laxatives. Not eliminating waste products regularly is probably more damaging to intestinal and overall health than the small potential risk of using stimulant anthraquinone laxatives. As with many other substances, overuse may cause problems.
Leung L. et al. Chronic Constipation: An Evidence-Based Review. Journal of American Board of Family Medicine (2011) 24: 436 (http://www.jabfm.org/content/24/4/436.full)