Weight gain has emerged as an important contributor to cancer incidence. Carrying additional weight in later life increases the risks, according to a Harvard University researcher.
"Avoiding weight gain is probably the most important thing that people can do after quitting cigarettes to avoid cancer," said Dr Walter Willett, chairman of the Department of Nutrition at the Harvard School of Public Health. "Even fairly moderate gains can add to the risk."
Dr Willett was addressing delegates in Belfast at the National Cancer Institute All-Ireland Cancer Conference, which finished yesterday. The conference included talks by some of the leading cancer specialists in the US, the Republic and Northern Ireland.
Many people gained a few pounds after their early 20s, Dr Willett said, and the number of extra pounds was directly related to relative risk. "The greater the weight gain, the greater the risk," he said.
Carrying an extra stone, for example, had been shown to increase cancer incidence of both breast and colon. If you put on an extra three stone between your 30s and 50s, you double the risk of these cancers.
"The issue of weight and weight gain seems to run across a number of important cancers," Dr Willett said. "The most important thing we have seen [in the studies] is staying lean and active. Controlling weight gain has important benefits for other things, including diabetes and heart disease," he added.
Dr Willett discussed a range of ways in which people could reduce their cancer risks, looking in particular at colon and breast cancer. He made reference to early theories about risk reduction that had "not held up in large studies".
A high fibre intake, for example, has been suggested as a way to prevent certain cancers. "It was a good hypothesis but it hasn't been held up in larger detailed studies," he said.
Suggestions that avoiding all fats could help reduce cancers had also failed the test of time, he said. Studies had shown, however, that there was a benefit in avoiding or reducing specific types of fat, including saturated fats typical of fried foods, and solid vegetable fats.
Dr Willett made particular reference to the benefits being discovered for the vitamin folic acid. "It seems to be important for so many things," he said. Low folic acid was linked some time ago to higher incidence of neural tube defects such as spina bifida. New work had shown that low folic acid levels was also associated with heart disease and cancers.
"Folic acid intake is a real problem in Ireland," he said, as evidenced by the State's relatively high rate of neural tube defects in new-borns. It was surprising that health officials had not introduced folic acid supplementation in foods such as breads and cereals as had occurred in the US.
It was easy to raise folic acid levels by taking a daily vitamin tablet containing the recommended 400 mg. "That is probably one of the most important things people can do for their health."
Alcohol consumption even at low levels was increasing the risk of cancers, he said. Moderate alcohol use increased the risk of breast cancer, but alcohol was also able to deactivate folic acid. Even one or two drinks a day could lower folic acid levels and increase risks.
Increasing intake of fruit and vegetables was still found to be valuable in reducing cancer risks and also the risk of heart disease, he said.
Women should also avoid prolonged use, beyond five years, of hormone replacement therapy to control the effects of menopause.
