Prevention of Recurrent Colorectal Adenomas (Colorectal or Colon or Bowel Cancer)
Most cases of colon cancer begin as small, noncancerous (benign) clumps of cells called adenomatous polyps. Over time some of these polyps become cancerous.Colorectal cancer is the second leading cause of cancer deaths in the United States. However, the number of new cases of colorectal cancer and the number of deaths due to colorectal cancer has decreased, which is attributed to increased sigmoidoscopic screening and polyp removal.The majority of the time, the diagnosis of localized colon cancer is through colonoscopy. Therapy is usually through surgery, which in many cases is followed by chemotherapy.
People who have any of the following symptoms should check with their physicians, especially if they are over 40 years old or have a personal or family history of the disease:
- a change in bowel habits such as diarrhea, constipation, or narrowing of the stool that lasts for more than a few days
- rectal bleeding or blood in the stool
- cramping or gnawing stomach pain
- decreased appetite
- weakness and fatigue
- jaundice (yellowish coloring) of the skin or sclera of the eye
Colorectal cancer, also called colon cancer or bowel cancer, includes cancerous growths in the colon, rectum and appendix. It is the third most common form of cancer and the second leading cause of death among cancers in the Western world. Many colorectal cancers are thought to arise from adenomatous polyps in the colon.The symptoms of colorectal cancer may resemble other conditions, such as infections, hemorrhoids, and inflammatory bowel disease. It is important to talk to the physician since finding colorectal cancer early makes successful treatment more likely.
From an epidemiological standpoint, there have been many studies linking calcium intake to colon cancer risk. Significant reductions in risk have been shown for the consumption of milk, dietary calcium and dairy products in general. Supplemental calcium in the diet or drinking water has been reported to decrease the colonic epithelial hyperproliferation induced by bile and fatty acids, enteric resection, a nutritional stress diet, and to suppress induction of the tumor-promotion enzyme ornithine decarboxylase. Calcium has also demonstrated an inhibitory effect on experimental colon carcinogenesis.
Calcium's effects on epithelial cells have demonstrated decreased proliferation and induced cell differentiation with increasing levels of calcium in vitro, similar in vivo effects in rodent and human colon, and decreased carcinogen-induced colonic tumor formation in rodents.In human subjects at increased risk for colon cancer, oral calcium supplementation significantly reduced colonic epithelial cell proliferation in most of the studies, including four randomized clinical trials.
Treatment with calcium supplements for 4 years appears to provide protection against recurrent colorectal adenomas -- the type of polyp that leads to cancer -- for up to 5 years after the supplements are stopped, new research shows. Beyond that point, however, no apparent effect is seen.
"In the Calcium Polyp Prevention Study, we showed that daily calcium supplementation was associated with a reduced risk of colorectal adenomas" in patients with a previous adenoma, study co-author Dr. John A. Baron, from Dartmouth Medical School in Lebanon, New Hampshire, told Reuters Health. The current data from the Calcium Follow-up Study indicates that the beneficial effect is prolonged, he added.
Baron said that experimental studies have suggested calcium may reduce the risk of colorectal adenomas (and colorectal cancer) by forming a complex with bile acids and preventing potential carcinogens from contact with the inner mucosal lining of the colon. He added that there is also evidence that calcium may have a specific effect on blocking formation of colon cells.
The Calcium Follow-up Study, which is reported in the Journal of the National Cancer Institute, included an analysis of data for 597 subjects who underwent at least one colonoscopy (a guided endoscopic colon exam to detect cancer) after the conclusion of the earlier Calcium Polyp Prevention Study. The average follow-up period after calcium supplementation stopped was 7 years.
In the first 5 years of the study, the rate of any adenoma formation among former calcium users was 31.5 percent, significantly lower than that of a comparison group of untreated patients at 43.2 percent.
Previous calcium use was also associated with a reduced risk of advanced adenomas, but the association fell short of statistical significance.
As noted, beyond 5 years, previous calcium use had no apparent effect on the adenoma risk.
Baron said he would like to see the current findings replicated in other studies. He emphasized that it is too early to recommend calcium supplementation as a means of staving off colorectal cancer and noted that there is some evidence that such use may actually increase the risk of prostate cancer.