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Half of U.S. cancer deaths linked to four unhealthy lifestyle behaviors

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Moderate-intensity aerobic physical activity, such as bicycling, is one of the four healthier lifestyle behaviors to adopt to reduce cancer risk.

Almost half of cancer deaths in the United States could potentially be prevented if people adopted just four healthier lifestyle behaviors, according to a study published last week in the journal JAMA Oncology.

The behaviors are ones we’re all familiar with: Stay tobacco-free. Maintain a healthy weight. Drink alcohol only moderately, if at all. And be physically active.

“These findings reinforce the predominant importance of lifestyle factors in determining cancer risk,” conclude the study’s authors. “Therefore, primary prevention should remain a priority for cancer control.” 

The authors — Drs. Mingyang Song and Edward Giovannucci of the Harvard T.H. Chan School of Public Health and Harvard Medical School — felt a need to conduct this new research because of a January 2015  study published in another journal, Science.

That earlier study had reported that random chance — the total number of random mutations a body tissue undergoes within its lifetime — was strongly correlated with lifetime cancer risk.

“This finding led some to conclude that only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions, while most is due to random mutations arising during stem cell division, so-called bad luck,” write Song and Giovannucci. “This study has been widely covered by the press and has created confusion for the public regarding the preventability of cancer.”

The two scientists wanted to help clear up that confusion.

Cancer is the second-leading cause of death (behind heart disease) in the U.S. It’s estimated that 1.6 million people living in the U.S. will be diagnosed with new cases of cancer in 2016, and 600,000 people will die from the disease.

Four risk factors

For their study, Song and Giovannucci used data collected from 89,571 women and 46,339 men who had participated in two large, ongoing studies, the Nurse’s Health Study and the Health Professionals Follow-Up Study. These volunteers had filled out questionnaires about their medical history and lifestyle every two years. They had also provided dietary information every four years.

Song and Giovannucci divided the participants into two groups: those with a low risk of developing cancer, based on their lifestyle, and those with a high risk. To be in the low-risk group, a participant had to meet all four of these requirements:

  • They must have never smoked or not smoked for five years before they were recruited into one of the research studies.
  • They must either not drink alcohol or drink only moderately (one or fewer drinks a day for women, two or fewer for men).
  • They must have a body mass index (BMI) of at least 18.5 and lower than 27.5.
  • They must engage in at least 75 minutes of vigorous-intensity or 150 minutes of moderate-intensity aerobic physical activity (such as running, walking, bicycling) weekly.

Among the 135,901 people whose data Song and Giovannucci analyzed, 21 percent met all four requirements and qualified as low-risk (12 percent of women and 9 percent of men). Everybody else was considered high risk.

Basic results

The researchers then compared the cancer rates between the low- and high-risk groups. Diagnoses of cancer were determined by the self-reported answers in the questionnaires. To identify cancer-related deaths, the researchers used data from the National Death Index.

They found that the incidence of cancer per 100,000 people was 463 for women and 183 for men in the low-risk group. That compared with 618 for women and 425 for men in the high-risk group. 

Song and Giovannucci then calculated something called population-attributable risk (PAR), the proportion of cancer cases that would not occur in a population if a risk factor was eliminated. In this study, that risk factor was having a lifestyle that did not include all four low-risk behaviors.

They estimated that 25 percent of the cancers diagnosed in women and 33 percent of those diagnosed in men could be attributed to the high-risk lifestyle factors. They also estimated that 48 percent of the cancer deaths in women and 44 of those in men could be attributed to those factors.

For individual cancers, the PARs — the proportion of diagnosed cancers estimated to be associated with high-risk lifestyle factors — were as follows:

  • Lung cancer: 82 percent for women, 78 percent for men
  • Colorectal cancer: 29 percent for women, 20 percent for men
  • Pancreatic cancer: 30 percent for women, 29 percent for men
  • Bladder cancer: 36 percent for women, 44 percent for men 

The researchers then compared the cancer risk for people in the low-risk group with that of the general U.S. population. The PARs for cancers resulting from a high-risk lifestyle were even higher in the general population (which had overall higher cancer rates).

They estimated, for example, that 41 percent of all cancers diagnosed in women in the U.S. general population and 63 percent of those diagnosed in men could be attributed to a high-risk lifestyle factors. For colorectal cancer, the PARS in both women and men were about 60 percent.

Limitations and implications

These findings should not be used to blame individuals with cancer for their illness, however. Nor should people who follow the four major healthy lifestyle behaviors feel they are somehow immune to the disease. 

Random mutations are undoubtedly still a factor in the development of cancer, as are environmental factors not related to lifestyle, such as exposure to toxic pollutants

This study comes with several important caveats. It was observational, which means it found a correlation between lifestyle and cancer risk, not a direct cause-and-effect link. In addition, most of the information for the study was collected from questionnaires, which are prone to bias. And the study included only health-care professionals, whose socioeconomic status and other factors may cause them to be healthier than the U.S. population overall. (Indeed, this analysis did find them healthier than the general population.)

Also, all the participants in this study were white, which means the findings may or may not be relevant for other ethnic groups. (The researchers said they used data only from white participants in the Nurses’ Health Study and the Health Professionals Follow-Up Study because there were not enough participants from other races in those studies to represent the general population.)

Song and Giovannucci point out, however, that the four behaviors evaluated in this study have been established as risk factors in diverse populations.

‘We need to avoid procrastination’

The two researchers — and others — hope that both the public and policymakers won’t be distracted by claims that cancer is just “bad luck.” We — as individuals and as a society — can take steps to lower our risk.

“We have a history of long delays from discovery to translating knowledge to practice,” writes Dr. Graham Colditz and Siobhan Sutcliff, two cancer prevention experts at Washington University in St. Louis, in an editorial that accompanies the study. “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.”

“It is these efforts that will be our fastest return on past investments in cancer research over the coming decades,” they add.

FMI: You can read the study and the editorial in full at the JAMA Oncology website

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