Last month two meta-analyses were published about health strategies on how to reduce the chances of developing bowel cancer. A meta-analysis is not a new piece of research, but it looks at all the published research on a subject, thus unifying conflicting results and drawing a conclusion out of the whole body of existing evidence.
The first one looked at more than 1.9 million participants in 25 studies which studied the benefits of dietary fiber, where single studies still produce conflicting results. Taking all the evidence together, the authors came to the conclusion that fiber from fruits, vegetables and legumes are not protective against bowel cancer, but that total fiber intake and fiber from cereals and whole grain reduce the chance of contracting bowel cancer significantly. Unfortunately it could not be established, whether smoking, lack of exercise, obesity and a diet high in fat, red meat or alcohol had an impact on the outcome.
A second meta-analysis with 12.000 participants only showed that long term treatment with low dose Aspirin showed a significantly lower probability of contracting bowel cancer, after it already had been shown that higher dose Aspirin lowered the cancer risk, but increased the risk of serious bleeding.
By presenting this news, I don´t necessarily present good news. In our pursuit of achieving longer and healthier lives, we have to acknowledge the fact that bowel cancer is common. Dietary changes, Aspirin and other life style changes alone cannot be relied upon to prevent the third most common cancer of the developed world; approximately 1 in 17 people will be affected by it during their lifetime.
Dietary and lifestyle changes certainly do improve the overall health of any individual, but everybody from the age of 50 onwards should think of additional strategies to prevent bowel cancer. This is particularly true, because it usually develops slowly. Most cancers develop from polyps and it is thought that it takes up to 10 years to change into a cancerous lesion. Knowing the natural history of its development and being a common disease makes it an ideal candidate for screening. The problem is most polyps never ever will develop into cancer, but there is no way foretelling which one will.
Currently there are 3 (4) accepted methods of screening. Yearly stool tests for occult blood (yearly means yearly) is the least invasive method, but also the least reliable one, too. A combination of 3yearly stool tests and 5yearly sigmoidoscopy would be an alternative. A sigmoidoscopy means a tube is being passed up the last 50cm of the large bowel where three quarters of the polyps occur. 10-yearly colonoscopies are regarded the gold standard, where the entire large bowel is looked at through a tube.
Unfortunately the latter two tests can cause serious complications in up to 2.5% of procedures; bleeding, perforation of the bowel, infection and exacerbation of diverticulitis. But with such procedures most polyps can be removed at the time of screening. A fourth, new screening procedure also seems to be very promising: virtual colonoscopy. This is a special computer tomographic investigation of the bowel, producing hundreds of images. The downside is a lack of experienced radiologists, the amount of radiation and last not least coincidental findings on the images in the rest of the abdomen, frequently leading to unnecessary further investigations.