Two studies released on Wednesday highlighted the risks and benefits of lifestyle choices in combatting cancer, showing the dangers of smoking for post-menopausal women and exercise's protective effect on the bowel.
Post-menopausal women who smoke, or who used to smoke, face an up to 16-percent higher risk of developing breast cancer compared to women who have never smoked, according to a paper published online by the British Medical Journal (BMJ).
Women who have been extensively exposed to passive smoking, either as children or in adulthood, could also be at greater risk of breast cancer, it added.
However, this apparent risk does not apply to women who were only moderately exposed to second-hand smoke.
The study covered almost 80,000 US women aged between 50 and 79 who were followed for 10 years.
In a separate investigation published in the British Journal of Cancer, people with an active lifestyle were found to be up to three times less likely to develop large bowel growths, known as polyps, which are often a precursor for cancer.
The conclusion is based on an overview of 20 published studies.
"We've long known that an active lifestyle can protect against bowel cancer, but this study is the first to look at all the available evidence and show that a reduction in bowel polyps is the most likely explanation for this," said lead author Kathleen Wolin of the Washington University School of Medicine in St. Louis, Missouri.
"Exercise has many benefits, including boosting the immune system, decreasing inflammation in the bowel and helping to reduce insulin levels -- all factors which we know are likely to have an effect on bowel polyp risk."
Half an hour's "moderate" exercise per day -- anything that leads to a slight shortage of breath -- and maintaining a reasonable weight are keys to reducing the risk of bowel cancer, said Cancer Research UK, which publishes the journal.