Colorectal cancer is the third most common type of cancer in both men and women. It is also the second most common cause of cancer death in the United States. About 57,000 Americans die from this disease each year, and 145,000 new cases are diagnosed. Only lung cancer leads colorectal cancer in cancer deaths.
All Americans should take steps to reduce their risk of colorectal cancer and be screened for it regularly, but people with Type 2 diabetes have even more reason to educate themselves about this deadly disease. That’s because they are at greater risk of developing it than the rest of the population. This article offers some suggestions for lowering your risk as well as guidelines for screening for early detection.
What is colorectal cancer?
Colorectal cancer is a cancer, or tumor, that forms in the colon (the large intestine) and/or rectum (the last 8 to 10 inches of the colon). The colon is where water and nutrients are reabsorbed into the bloodstream as the last stage of digestion. At this point only waste remains. The waste is then eliminated through the rectum and anus.
Symptoms of colorectal cancer can include a change in bowel habits, blood in the stool, lower abdominal pain or cramping, fatigue, and vomiting. In the early stages, however, there are no symptoms. The early stages are also the time when it is easiest to cure. That’s why regular screening is so important. However, because so many Americans do not get screened according to the schedule recommended by the American Cancer Society, only about 39% of cases of colorectal cancer are found in the early stages.
Most cases of colorectal cancer develop from precancerous polyps, or adenomas. Polyps are growths in the colon that occur frequently in people over 50. Although most polyps are benign, or noncancerous, they can become malignant, or cancerous. While only 5% to 10% of all polyps become cancerous, all polyps should be surgically removed to test for cancer.
Some of the risk factors for colorectal cancer are modifiable, and some are not. Age is one that is not: 93% of people who develop colorectal cancer are over age 50. The average age at diagnosis is mid-60s.
Having a family history of colorectal cancer or a personal history of ulcerative colitis, Crohn’s disease, or a previous history of colorectal cancer is also a risk factor for colorectal cancer.
A rare, hereditary form of colorectal cancer is called hereditary nonpolyposis colon cancer, or HNPCC. Only 2% of all colorectal cancers fall into this category. The average age at diagnosis for this colorectal cancer is 44.
Another rare, inherited condition that raises the risk for colorectal cancer is familial adenomatous polyposis (FAP), in which hundreds of polyps form in the colon or rectum. When FAP is left untreated, colon cancer usually occurs by age 40. Only 1% of all colon cancers occur from FAP.
People with Type 2 diabetes have a 30% to 40% increased risk of colorectal cancer. While this connection is still being studied, there is evidence that hyperinsulinemia, or high levels of circulating insulin, increases the risk of colon cancer. It is thought that high insulin levels can damage the mucosa, or lining of the colon. Hyperinsulinemia is often associated with insulin resistance, in which the body’s cells are resistant to the action of insulin, so more insulin is needed to allow glucose into the cells. Insulin resistance is one of the major causes of high blood glucose levels in Type 2 diabetes.
Recent research studies have also suggested that people with Type 2 diabetes who have been on insulin therapy for more than one year have an increased incidence of colorectal cancer. However, more research needs to be done to clarify this issue. In the meantime, people who currently take insulin should not stop taking it. But they should follow the screening guidelines for early detection of colorectal cancer. It is estimated that with early detection and removal of polyps, risk for this disease can be decreased by 70%.
Obesity also raises the risk of colorectal cancer. In fact, it is estimated that 3.2% of all new cases of cancer in the United States have an association with obesity. Obesity and overweight are also responsible for 14% of cancer deaths in men and 20% in women. The National Institutes of Health defines overweight as a body-mass index (BMI) of 25.0 to 29.9, and obesity as a BMI greater than 30. To calculate your BMI, divide your weight in pounds by your height in inches, then divide that result by your height in inches again. Multiply that result by 703. In other words, weight ÷ height ÷ height × 703.
It has been estimated that 70% of the cases of colorectal cancer in Western countries could be prevented through changes in lifestyle. While many lifestyle factors are mentioned in this article, the best path to successful prevention of colorectal cancer includes all of these factors. However, incorporating even a single lifestyle change is beneficial.
The influence of diet
Many studies have examined the connection between diet and the risk and incidence of colorectal cancer. While there are still many unknowns, it’s clear that following a nutritious diet high in fruits and vegetables and low in red and processed meats and saturated fat is likely to be beneficial.
Meat. A large study published in 2005 showed that a diet high in processed and red meat increases the risk of colorectal cancer. It additionally found that a high consumption of poultry and fish was associated with a lower risk.
Processed meats include bacon, bologna, ham, hot dogs, luncheon meat, salami, sausages, and other beef and pork products preserved by salting, smoking, or adding nitrites or nitrates. Red meat includes beef, pork, lamb, liver (including chicken livers), and veal. In the study, a high intake of red meat was defined as 3 or more ounces a day for men and 2 or more ounces a day for women.
The study did not determine the mechanism by which red or processed meat increases colorectal cancer risk. But the take-home message is clear: By decreasing the amount of processed and red meat in the diet and eating more fish and poultry, many cases of colorectal cancer could be prevented.
Other studies have shown that grilling meat — including red meats, chicken, and fish — at high temperatures can produce cancer-causing, or carcinogenic, compounds, among them chemicals known as heterocyclic amines. The longer and hotter the cooking method, the more compounds are formed. These compounds have been linked to colon cancer as well as to breast and prostate cancer.
Fruits and vegetables. Many studies have shown that a high intake of fruits and vegetables not only protects against colorectal cancer but also against many other types of cancer, cardiovascular disease, and Type 2 diabetes. Fruits and vegetables contain vitamins, minerals, fiber, antioxidants, and other nutrients. The allium vegetables — onion, garlic, scallions and leeks — have a strong protective effect against colorectal cancer. Green vegetables, carrots, and cruciferous vegetables also have a protective effect. Cruciferous vegetables, which include broccoli, cauliflower, cabbage, and Brussels sprouts, contain a chemical called sulforaphane, which protects against many kinds of cancer. Chlorophyll in green vegetables binds to cancer-causing chemicals — including the heterocyclic amines that are formed when foods are grilled — and forms a large molecule that is excreted from the body in feces rather than being absorbed.
However, there are many different types of nutrients in vegetables that are protective, so it is probably not one single nutrient but the combination of nutrients working together that has protective effects.
Calcium. At least two studies have found that consuming at least 1200 milligrams of calcium per day — either in the form of supplements or supplements and food — for several years reduces the risk of developing colorectal adenomas. Calcium binds bile and fatty acids in the colon, which decreases exposure to carcinogenic chemicals. Dairy products, such as milk, cheese, and yogurt are good sources of calcium, but full-fat varieties are also high in saturated fat. When consuming dairy products, choose low-fat cheese, skim or 1% milk, and low-fat or nonfat yogurt.
Omega-3 fatty acids. Omega-3 fatty acids found in fish and some nuts and seeds decrease the inflammation associated with the initial stages of colon and other cancers.
Folate and alcohol. Folate, also called folic acid, is a B vitamin and is combined with vitamins B6 and B12 for healthy cell development. A diet low in folate can lead to precancerous cells. Since there is a rapid turnover of cells in the colon, and therefore a greater need for folate in these cells, a low folate intake is a risk factor for colorectal cancer. Folate is found in dark-green, leafy vegetables such as spinach and turnip greens, citrus fruits and juices, and dried beans and peas. Since 1996, the Food and Drug Administration has required that folic acid be added to enriched breads, cereals, flours, pasta, rice, corn meals, and other grains.
Alcohol interferes with folate metabolism, so heavy drinkers have an increased need for folate. In fact, people who have a diet low in folate and high in alcohol have an increased risk of colorectal adenomas. People who are heavy beer and liquor drinkers have been shown to have an increased risk of colorectal cancer, while those who drink wine have a decreased risk. It is recommended that beer and liquor be limited to no more than one drink a day. Getting enough folate can also help to prevent polyps from reoccurring.
Vitamin D. Vitamin D is a fat-soluble vitamin that is synthesized in the skin by sunlight and is found in some foods. There is some evidence that high blood levels of vitamin D have a protective effect against colorectal cancer. Good food sources of vitamin D include salmon, sardines, mackerel, and other fatty fish. Milk has been fortified with vitamin D since the 1930’s to prevent rickets.
Normally, exposure to sunlight provides the body with all of its vitamin D needs. However, in the northern parts of the United States, sun exposure in the winter months does not supply enough skin synthesis of vitamin D. Cloudy days, use of sunscreen, and shade also decrease skin synthesis. Perhaps not surprisingly, there is a higher incidence of colorectal cancer in the North than the South. Older people also do not synthesize vitamin D in the skin as effectively as younger people.
Vitamin D helps to absorb calcium during the digestive process, so taking a multivitamin containing vitamin D is recommended for adults over 50, people who live in northern latitudes, and people who get limited sun exposure for any reason.
Fiber. The link between dietary fiber intake and colorectal cancer is controversial. While many studies have been done on the effects of fiber consumption on colorectal cancer, the findings have been inconsistent.
It has been suggested that the inconsistency comes from the type or source of fiber being studied. There are two types of fiber: soluble and insoluble. Both types of fiber come from plant foods. Fruits and vegetables, which contain both soluble and insoluble fiber, appear to have the most benefit, while wheat fiber, which is primarily insoluble, and psyllium, which is about 70% soluble and 30% insoluble, do not seem to provide protection against colorectal cancer.
While researchers continue to seek out answers to this question, there are still plenty of good reasons to eat whole grains and at least five servings of fruits and vegetables each day as part of a healthy lifestyle.
Other lifestyle influences
Stopping smoking and performing regular physical activity are beneficial for many reasons, including lowering your risk of colorectal cancer.
Cigarette smoking. Smokers have a 30% to 40% increased risk of colorectal cancer compared with nonsmokers. Cigarette smoking increases the likelihood both of developing adenomas and of their becoming cancerous.
Physical activity. Having a sedentary lifestyle has also been implicated as a risk factor for colorectal disease. Studies have shown a 50% decrease in risk of colon cancer among people who walk briskly three to four hours a week. People who are even more physically active may be able to decrease their risk of colon cancer by 70%. Increasing one’s level of physical activity can also prove beneficial in preventing many other diseases such as cardiovascular disease and in controlling Type 2 diabetes.
Aspirin. Regular aspirin use has been shown to help prevent colorectal cancer, but taking aspirin for the sole purpose of preventing cancer is not recommended at this time. The side effects of aspirin, such as bleeding in the stomach, outweigh the benefits.
Energy balance. Cancer researchers use the term “energy balance” to describe the interaction of diet, physical activity, and genetics, the effect of this interaction on growth and body weight over a person’s lifetime, and the ways in which these factors may influence cancer risk. The National Cancer Institute is currently supporting research into the complex issue of energy balance, or energetics, and its effect on cancer outcomes.
One step at a time
The best path to successful prevention of colorectal cancer incorporates all of the diet and lifestyle recommendations mentioned in this article. However, making even a single lifestyle change is beneficial. Most important, people with diabetes should follow the American Cancer Society’s screening guidelines for colorectal cancer to detect the disease early if it develops. (For more information about colorectal cancer prevention and treatment, see “Cancer Resources.”)