Healthy lifestyle 'stacks the deck' for cancer prevention

Up to 40 per cent of cancer cases and about half of cancer deaths among some Americans might be prevented if people followed healthy habits, researchers estimate. 

Population studies have established smoking, drinking alcohol, obesity and lack of physical activity as factors that increase cancer risk. But this body of knowledge was challenged last January by the so-called "bad luck" study that compared cancer incidence and stem cell divisions. It created confusion about how preventable cancer is because it was often interpreted to mean bad luck drives most cancer.   

Now researchers at Harvard Medical School have examined cancer prevention using the more traditional approach in a large group of Americans today.

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In a study published in Thursday's issue of JAMA Oncology, men and women were placed in the low-risk category for cancer risk if they met four criteria of a healthy lifestyle pattern:

• Never or past smoking of less than five years.
• No or moderate alcohol drinking — one drink a day or less for women and two drinks a day or less for men.
• Body mass index, an indicator of excess weight for height, of at least 18.5 and lower than 27.5.
• Weekly physical activity of at least 75 minutes of vigorous-intensity or 150 minutes of moderate intensity.

Of the more than 89,000 female registered nurses and 46,000 male health professionals in the study, 16,531 women and 11,731 men had a healthy lifestyle pattern and the rest were placed in the high-risk group.

Dr. Mingyang Song of Massachusetts General Hospital and Dr. Edward Giovannucci at Harvard T. H. Cahn School of Public Health in Boston analyzed data following the two groups starting in 1976 for the women and 1986 for the men. This study followed participants until 2012. 

Lifestyle factors tops 

The health professionals filled in detailed questionnaires about their medical history and lifestyle every two years and diet questionnaires every four years. The researchers also checked medical records and national databases of deaths and cancer surveillance for comparisons with the general U.S. population.

"In the two cohort studies of U.S. white individuals, we found that overall, 20 per cent to 40 per cent of carcinoma cases and about half of carcinoma deaths can be potentially prevented through lifestyle modification," the researchers concluded.

"Lifestyle factors remain the most important factor for cancer incidence and mortality," Song added in a journal podcast.

What's more, the researchers said, about 80 per cent to 90 per cent of lung cancer deaths could be avoided by adopting the healthy lifestyle habits of the low-risk group, mainly by butting out.

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The researchers defined as overweight those with a body mass index of 27.5, instead of the usual 25, to include less common cancers.

In Canada, the healthy range for adults is a body mass index of 18.5 to 24.9. 

They said since the participants were mainly white, they included only whites in their analysis.  

While health professionals might be expected to be more health conscious about cancer screening than others, Song said they were surprised to find little difference between the two groups for screening.

The reduction in cancer mortality among male health professionals was largely due to lower incidence, which they said argues against the idea that this group had access to better treatments.   

Most cancer is preventable, with estimates as high as 80 per cent to 90 per cent for smoking-related cancers, such as lung and oropharyngeal cancer and as high as 60 per cent for colorectal and bladder cancer, Dr. Graham Colditz and Siobhan Sutcliffe of Washington University School of Medicine in St. Louis said in a journal editorial published with the study, titled The Preventability of Cancer: Stacking the Deck.

"As a society, we need to avoid procrastination induced by thoughts that chance drives all cancer risk or that new medical discoveries are needed to make major gains against cancer, and instead we must embrace the opportunity to reduce our collective cancer toll by implementing effective prevention strategies and changing the way we live," the editorial concluded.

The editorial authors suggested guidelines and reimbursements to encourage doctors to counsel patients and their families about healthy lifestyles.

In the study, skin, brain, lymphatic and hematology cancers that likely have strong environmental causes were excluded. Genetics and age also contribute to cancer risk.

The Canadian Cancer Society expects cancer  cases to increase by about 40 per cent by 2030 as the population ages and grows.

The study was funded by the U.S. National Institutes of Health.