As reported in the Journal of Internal Medicine, the intervention did not reduce the overall cancer risk in the very long term.
The study is a 43-year follow-up of the Oslo diet and antismoking study, which recruited men at high risk for cardiovascular disease in 1972-73. Previous research revealed that the counselling intervention had a clear benefit for reducing cardiovascular disease risk in these men.
So far, evidence for effects of lifestyle interventions on cancer have been limited, but this Norwegian study showed that advice for a heart-friendly lifestyle also could prevent some cancers in the long term.
"This study showed that changes to a healthier diet and stopping smoking in adult life will reduce risk of some lifestyle-related cancer forms, which are on the rise in the population", said senior author Dr. Paula Berstad, of the Cancer Registry of Norway.
Difference peaked after 25 years
Lower cancer incidence became visible 18 years after the healthy changes began.
In men who were either overweight or smokers at the start of the study, researchers found a lower incidence of cancers associated with obesity, lifestyle or smoking up to 25 years afterwards. Cancer of the digestive organs and urinary tract were among the cancer forms affected - cancers that have otherwise increased in the Norwegian population over the last decades.
The largest difference was seen in the digestive system. Obese men and smokers who received counseling had 45 percent lower risk of cancer in the digestive system after 25 years, compared with the control group.
In total, 20 percent of those who were overweight or smoked had cancer after 25 years.
The differences were most marked 25 years after the study started. After that, the groups have approached each other again.
"We know that in most cases, high age is the most important risk factor for cancer. Today, the participants in this study are in their 80's, and not unexpectedly, the cancer rates approach each other for the two groups. But when they were in the 60's, the group who received guidance had a clear advantage compared to the control group, "says Berstad.
Long term effect
"Cancer takes a long time to develop. Exposure to a carcinogenic substances, or the opposite - exposure to a healthy lifestyle, appears in the cancer risk many years later", says Berstad.
She points out that the men in this survey managed to make lasting changes, and maintain the good diet for a long time.
"With good health registries, which enable us to follow their cancer risk over time, this study proved that healthy changes have an effect," continues Berstad.