Of all the cancers proposed to have a relationship to vitamin D, perhaps colon cancer has the strongest connection. More properly called colorectal cancer because the disease may involve any part of the large intestine, including the rectum, colorectal cancer can be picked up in early and curable stages with proper screening.
Colorectal cancer risk factors and symptoms
More than 80 percent of colorectal cancers are spontaneous and not related to family history. The cancers that form in the first part of the colon (proximal), last part of the colon (distal), and the rectum can form for different reasons.
Colorectal cancer usually develops in mushroom-shaped growths called polyps that extend from the inner lining of the colon or rectum into the lumen. Most polyps aren’t malignant, but some develop into cancer.
A number of factors can increase the risk of developing colorectal cancer:
African American background
Alcoholism
Diet high in red meats, especially processed meats like luncheon meats
Family history of colorectal cancer
History of colorectal polyps
History of inflammatory bowel disease, including ulcerative colitis and Crohn’s disease
Obesity
Older age (much more common after age 50)
Physical inactivity
Smoking
Colorectal cancer has many signs and symptoms after it has enlarged or spread. The major ones include the following:
Bowel obstruction when the tumor blocks the colon and prevents stool from moving through the intestine. This is uncomfortable and can lead to vomiting and life-threatening infection of the abdomen if the colon tears due to the strain (perforation).
Change in bowel habits (constipation or diarrhea)
Constitutional symptoms like weakness due to anemia, weight loss, and fever
Dark stools from breakdown of blood in the colon
Jaundice if the tumor spreads to the liver
Rectal bleeding
Colorectal cancer screening methods
Excellent screening methods are available to detect colorectal cancer or polyps. Most screening turns up polyps or pre-cancerous growths. These are removed as a precautionary measure but don’t specifically predict that a person will get a colon tumor later.
Colorectal screening methods include these major forms:
Colonoscopy, visual examination with a long, flexible video camera that can be used to see most of the colon. If everyone over the age of 50 did this once every five years colonoscopy may reduce the death rate from colorectal cancer by 80 percent.
Examination of the rectum by the doctor’s gloved finger. Many tumors can be felt if they’re in the rectal area.
Identification of carcinoembyronic antigen, a protein that the body produces when colorectal cancer is present. Details about the antigen can provide doctors with information about the size of the tumor.
Sigmoidoscopy, direct visual examination with a short, stiff tube inserted into the rectum. This is like a colonoscopy but doesn’t look as far into the colon.
Testing of the stools for blood.
Virtual colonoscopy, using X-rays to see inside the colon. This form still requires visualization with a sigmoidoscope or colonoscope to do a biopsy, if necessary.
Colorectal cancer is staged to define the severity of the cancer and provide a basis for a person’s treatment and prognosis. Treatment of colorectal cancer begins with surgery for the original cancer and for any spread that has occurred, if possible.
After surgery, the patient undergoes chemotherapy in an effort to kill any remaining cancer cells and to prevent future spread of the disease. Many drugs and numerous regimens of treatment are used. Radiation therapy is done for rectal cancers but not for colon cancers.
Follow-up exams are done every three to six months after treatment for colon cancer. These can reduce the death rate from colon cancer by a substantial amount.
Vitamin D’s possible role in colon cancer
Colorectal cancer was one of the first cancers proposed to be associated with low vitamin D status. These first studies showed:
The incidence of colorectal cancer is higher the farther north people live, where they’re less able to make vitamin D in the skin during long winters.
Mortality (death) rates from colorectal cancer in the United States are highest in populations exposed to the least amount of natural sunlight.
In the last two decades the evidence that vitamin D deficiency plays a role in colorectal cancer has greatly increased. Some major discoveries confirm this role:
Calcitriol and synthetic drugs similar to it suppress the growth of colon cancer cells in cell culture experiments by reducing the production of new cancer cells, preventing colon cells from becoming abnormal, causing the death of cancer cells (apoptosis), and preventing blood vessels from feeding cancer tumors.
Drugs designed to function like calcitriol reduce development of colon cancer caused by chemicals in mice and rats.
Diets deficient in vitamin D cause mice to develop colon tumors and for tumors to grow more quickly.
In mice that don’t have the gene for the vitamin D receptor needed for the action of calcitriol, the cells of the colon multiply faster and acquire DNA damage that could lead to cancer-causing gene mutations.
Vitamin D intakes less than 150 IU a day are associated with developing more colon cancer compared to intakes more than 500 IU per day.
Whether measurements of serum 25OH vitamin D are looked at directly or indirectly, an inverse relationship exists between vitamin D status and both occurrence and severity of colon cancer.
This all suggests that one secret to preventing colon cancer is to avoid vitamin D deficiency. The question should be settled definitively within the next five years or so because a large clinical study called VITAL is randomizing 20,000 people to take higher doses of vitamin D versus placebo and looking to see if colorectal and other cancers are decreased.