Cancer cells are abnormal cells that multiply excessively to form a malignant mass or tumour. These cells can invade surrounding tissue and may travel through the blood stream or lymph vessels to other areas of the body where they can form secondary cancers called ‘metastases’. Cancer cells sometimes consume a large amount of the body’s nutrients, which causes weight loss and tissue wasting.

Many cancers are removed surgically. Surgery may be followed, or preceded, by radiation therapy, chemotherapy or both. Some cancer cells are, however, resistant to the drugs used in chemotherapy. Furthermore, these drugs have unpleasant side effects causing nausea and vomiting, hair loss, fatigue and suppression of the immune system. Radiation therapy with x-rays also causes adverse effects including burning of the skin and it destroys healthy tissue as it passes through the body to the cancer cell mass.

People with colorectal cancer can be treated effectively if the cancer is diagnosed and treated in its early stages. Colorectal cancer is rarely diagnosed in people less than 40 years of age meaning that people affected are often elderly. Environmental factors related to lifestyle, including diet, obesity, physical inactivity, smoking and alcohol consumption may play an important role in the development of colorectal cancer. High fibre, fruit and vegetables, folate (a water-soluble B vitamin) and methionine (an essential amino acid) intake are considered to be protective. The incidence is most common in industrialised societies and lowest in Asia, including China and Japan, and Africa.

We present some of the evidence from Cochrane systematic reviews about complementary and alternative treatments related to prevention of cancers. This evidence comes from carefully researched reviews of information about clinical trials done to evaluate medical treatments. Studies are only included in these reviews if they meet pre-defined criteria.

DIETARY FIBRE FOR THE PREVENTION OF COLORECTAL CANCER

Colon cancer is one of the leading cancers in men and women and is more common in industrialised societies. The risk of colorectal cancer begins to increase after the age of 40 years and rises sharply from the age of 50 to 55 years. Early detection and treatment may have some effect on reducing the mortality from colon cancer but prevention is the more important goal.

Most colorectal cancers develop from a type of slowly growing benign polyps (adenomatous polyps). These polyps are considered a ‘biomarker’ for increased risk of colorectal cancer. A decrease in the number of polyps could potentially indicate a decrease in the incidence of cancer in the large intestine or rectum.

What is known

Genes, diet and lifestyle all seem to be important factors in the development of colorectal cancer, which is especially prevalent in industrialised countries. Several communities with low rates of this type of cancer have diets that are rich in fibre. However, descendents of immigrants from these countries who grow up in an industrialised country take on the higher incidence of that industrialised country (for example American born Chinese). Increasing the levels of fibre in the diet of people living in industrialised countries might, therefore, help to reduce the incidence of polyps and the rate of colorectal cancer.

There is no internationally accepted definition of fibre. It is classified as soluble (for example pectin from fruit and some vegetables or agar from seaweed) or insoluble (for example wheat bran).

What the research says

Overall, there was no evidence that a high-fibre diet decreased the recurrence of adenomatous polyps. When the data was combined there was no difference found between those on the high-fibre diet compared to those on a regular western diet.

This conclusion is based on five trials that reported the number of participants who developed at least one polyp. Similarly, the combined results from two studies recorded the number of participants who developed more than one polyp and also indicated that the high-fibre diet did not decrease the risk of recurring polyps.

The combined results of four studies that looked at the number of participants with polyps greater than 1 cm in size also did not find any evidence that a high-fibre diet decreased the risk of these larger polyps. The type of high fibre eaten did not alter these conclusions.

How it was tested

The researchers made a thorough search of the medical literature and found five controlled trials with 4349 participants who had a history of adenomatous polyps but no diagnosis of colorectal cancer. All of the participants had undergone a procedure to remove existing polyps.

Participants were randomly assigned to a high-fibre diet or to a regular western diet with (and in one trial without) placebo and followed for between two to four years to see if there was a difference in the number of people who developed polyps in the two groups.

The two largest studies were from the USA and the other studies were conducted in Europe, Australia, and Canada. The type of fibre added to the diet in the studies included wheat bran fibre, ispaghula husk (another type of fibre), or a comprehensive high fibre diet.

Side effects and general cautions

Most trials did not report information about adverse events. In one trial no side effects were evident with the high-fibre diet.

One of the problems in determining whether high-fibre diets can prevent colorectal cancer is that the randomised controlled trials need to be larger and go on for longer than the trials included in this review. For this reason, the trials set out to look at the recurrence of polyps.

Source

Asano TK, McLeod RS. Dietary Fibre for the prevention of colorectal adenomas and carcinomas. The Cochrane Database of Systematic Reviews 2002, Issue 1. Art. No.: CD003430. DOI: 10.1002/14651858.CD003430.

DIETARY CALCIUM SUPPLEMENTATION FOR PREVENTING COLORECTAL CANCER

Colon cancer is one of the leading cancers in men and women and is more common in industrialised societies. The risk of colorectal cancer begins to increase after the age of 40 years and rises sharply from the age of 50 to 55 years. Early detection and treatment may have some effect on reducing the mortality from colon cancer but prevention is the more important goal.

Most colorectal cancers develop from a type of slowly growing benign polyps (adenomatous polyps). These polyps are considered a ‘biomarker’ for increased risk of colorectal cancer. A decrease in the number of polyps could potentially indicate a decrease in the incidence of cancer in the large intestine or rectum.

What is known

Calcium is one of the dietary factors that may potentially prevent colorectal cancer. Other dietary factors include reduced fat and increased carbohydrate, high fibre and good fluid intake. The calcium is thought to protect the membrane (mucosa) lining the bowel.

What the synthesised research says

Taking a daily calcium supplement may have a small to moderate protective effect against recurring adenomatous polyps.

Only two trials involving a total of 1346 people contributed to this conclusion. Both controlled trials reported on the number of people who developed at least one recurrent polyp (adenoma). The amount of calcium taken daily was 1200 mg in one trial and 2000 mg in the second trial.

How it was tested

The researchers made a thorough search of the literature. They found two controlled trials that randomly assigned people who had previously had polyps to receive either a calcium supplement or a non-active treatment (placebo) daily for three to four years.

Side effects and general cautions

The trials did not have enough people involved for any meaningful conclusion to be drawn about whether dietary calcium prevented colorectal cancer.

Colorectal cancer is sufficiently rare that it is extremely difficult to conduct a controlled trial large enough and lasting long enough to identify the protective effect of any given single nutrient or nutritional supplement like calcium. That is why researchers rely on the indirect evidence supplied by studying the development of the far more common adenomatous polyps, some of which may be pre-cancerous.

Source

Weingarten MA, Zalmanovici A, Yaphe J. Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps. The Cochrane Database of Systematic Reviews 2005, Issue 2. Art. No.: CD003548.pub3. DOI: 10.1002/14651858.CD003548.pub3.

ANTIOXIDANT SUPPLEMENTS FOR PREVENTING GASTROINTESTINAL CANCERS

Invasive cancer continues to be a world health problem. The possibility that antioxidant supplements such as vitamins A, C, E, beta-carotene (a source of vitamin A) and the trace element selenium may protect against cancer has drawn much attention. Broccoli, cabbage, cauliflower and brussel sprouts are good sources of vitamins A and C. Antioxidants can protect against oxidative stress, which damages cells and could affect their ability to stop the development of cancer.

What is known

Antioxidants may prevent gastrointestinal cancers but this varies in the different regions of the gut. High consumption of fruits and vegetables may prevent oesophageal and gastric cancers.

Antioxidants may inhibit the growth or progression of the type of polyps from which colorectal cancer can develop and reduce chronic inflammation to protect against pancreatic cancer. In the liver, viral infection with hepatitis B or C or alcohol damage causes oxidative stress which could play a role in the development of liver (hepatocellular) cancer.

What the research says

Antioxidant supplements did not influence the incidence of oesophageal, gastric, colorectal, pancreatic, or liver cancers. Supplements used were beta-carotene (a source of vitamin A), vitamin A, vitamin C, vitamin E, or combinations. A benefit was seen with selenium on gastrointestinal cancers.

These conclusions were based on 14 trials involving 170,525 people. None of the trials reported on the incidence of small intestinal or biliary tract cancers.

In four trials, selenium showed a significantly lower incidence of gastrointestinal cancers. Only one of the trials was of high quality.

Participants in the various trials had different degrees of risk of developing gastrointestinal cancers. Nine trials included people who had a high risk of cancers; three included healthy people and one trial included people at a high risk for cardiovascular disease.

How it was tested

The researchers made a thorough search of the literature and found 14 controlled trials that included a total of 170,525 participants. The number of people in each trial ranged from 226 to 39,876. Their ages varied from 15 to 84 years, with a mean age of 55 years. The people were randomly assigned to receive either oral antioxidants or non-active (placebo) capsules or tablets. Some trials used a combination of antioxidants.

All together, nine trials tested beta-carotene (15 to 50 mg), four trials vitamin A (5000 to 50,000 IU), four trials vitamin C (120 to 2000 mg), five trials vitamin E (30 to 600 mg); taken daily or on alternate days for 1 to 12 years. Six trials tested selenium (50 to 228 mg), taken daily for two to four years.

Side effects and general cautions

Beta-carotene increased yellowing of the skin and caused belching in some people.

There was some indication that antioxidants, particularly a combination of beta-carotene and vitamin A or vitamin E, might increase overall deaths. Nine trials (seven of high quality and two of low quality) provided information on this. People in the various trials had different degrees of risk of developing gastrointestinal cancers, which could have influenced the results.

Source

Bjelakovic G, Nikolova D, Simonetti RG, Gluud C. Antioxidant supplements for preventing gastrointestinal cancers. The Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD004183.pub2. DOI: 10.1002/14651858.CD004183.pub2.