People who have a parent or sibling with colon cancer can markedly reduce their own chances of developing the disease by taking a daily multivitamin that includes folic acid and limiting their intake of alcohol, according to a new study by researchers at Dana-Farber Cancer Institute, Brigham and Women's Hospital and Harvard School of Public Health in the US.
The findings, published in the March issue of Cancer Epidemiology, Biomarkers and Prevention, join a small but growing body of evidence that dietary and behavioural changes can reduce the risk of some cancers in people who may have an inherited tendency to develop them.
"Previous research has demonstrated that people's risk of developing colon cancer is two times greater if they have a parent or sibling who has been diagnosed with the disease," said study leader Charles Fuchs of Dana-Farber. "Our study points to steps that such individuals can take to substantially lower those odds."
Studies have shown that a variety of diet and behavioural modifications - such as stopping smoking, eating a diet high in fruits and vegetables, avoiding heavy red meat consumption, and having regular colon exams after age 50 - can reduce colon cancer risk in the general population. In the new study, Dr Fuchs and his colleagues asked whether any of these measures are especially effective in people with a family history of the disease.
The researchers collected data from the Nurses' Health Study, a project which has been tracking the health of 121,700 female registered nurses in the United States for more than 25 years. The study, run by researchers at BWH, maintains an extensive databank of participants' dietary and lifestyle habits, making it possible to explore the relation between people's behaviour and their risk of developing certain diseases.
The team analysed information from 88,758 nurses whose family health histories and dietary habits were recorded in the database. It focused on behaviours known to be associated with colon cancer to see if any were particularly helpful or harmful in people with a family history of the disease.
Three particular patterns emerged from the research. A diet high in folic acid, high in methionine (an essential amino acid), and low in alcohol intake, when followed for at least five years, reduced colon cancer risk much more sharply in those with first-degree relatives who had the disease than in those without such a family history. Although all the study participants were women, Dr Fuchs contended there is no reason to think the results do not apply to men as well.
Participants with a family history of colorectal cancer who consumed low-folate diets were 2.5 times more likely to develop colon cancer than similar individuals who did not have a family history. In contrast, among participants on a high-folate diet, those with a family pattern of colorectal cancer did not experience any significant increase in colon cancer risk compared to those without such a pattern. "It appeared that either a high-folate diet or use of folate-containing multivitamins virtually eliminated the excess risk of colon cancer associated with a family history of the disease," Dr Fuchs explained.
While folic acid is found in fruits and vegetables and products made with enriched flour, obtaining the high levels tracked in the study - 400 micrograms a day - can be easily achieved by taking a multivitamin, Dr Fuchs said. The quantity of alcohol consumption that appeared to increase the risk associated with a family history was greater than two glasses of wine per day.
The findings around methionine are more complicated. While high levels of the nutrient were shown to reduce the influence of a family history of colorectal cancer on the development of the disease, high amounts also may be associated with the "hardening of the arteries" that can lead to heart attacks. As a result, dieticians do not recommend taking methionine supplements.
The new study not only provides guidance to people with family risks of colon cancer, Dr Fuchs commented, but also may point toward a better understanding of the biology of the disease. Scientists know that folic acid, methionine, and alcohol all affect a process known as methylation, in which specialised compounds of hydrogen and carbon are attached to various structures and products of cells.
Methylation plays a vital role, for example, in creating the building blocks of DNA within cells. Without sufficient methylation, the DNA structure may become unstable, raising the prospect of certain diseases, including cancer.
It is possible that families with a pattern of colon cancer may have some modest alteration in either DNA processing or repair that makes them particularly susceptible to deficiencies in the methylation process, Dr Fuchs said.
"This research may make it possible to identify genes that confer a greater risk of the disease in families with a history of it. That would be an important step toward therapies able to reduce that risk. Our findings involving folate may offer a first clue," he concluded.