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Lifestyle changes can reduce cancer incidence, mortality
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The adoption of healthy lifestyle practices may prevent a large proportion of cancers and reduce cancer mortality in the United States, according to results of a prospective cohort study.
“Epidemiologic studies have established several lifestyle factors that increase cancer risk, such as smoking, alcohol use, obesity and physical inactivity,” Mingyang Song, MD, ScD, research fellow at Harvard T.H. Chan School of Public Health, and Edward Giovannucci, MD, ScD, associate professor of medicine at Harvard Medical School and professor of nutrition and epidemiology at Harvard T.H. Chan School of Public Health, wrote. “However, this substantial body of knowledge has been challenged by a recent study, which found a high correlation between the number of stem cell divisions of a given tissue and the lifetime risk [for] cancer in that tissue.”
Edward Giovannucci
The results of this study — conducted by Tomasetti and Vogelstein and published in Science — appeared to conclude that only one-third of the variation in cancer risk is attributable to lifestyle factors or inherited predispositions. All other cancers, then, were attributed to random mutations, or “bad luck.”
Song and Giovannucci sought to estimate the proportion of cancer incidence and death among non-Hispanic white individuals in the United States that could be potentially prevented by lifestyle changes.
They analyzed cancer and lifestyle data from the Nurses’ Health Study, the Health Professionals Follow-Up Study, and national cancer statistics to prospectively evaluate associations between lifestyle factors and cancer incidence and mortality.
The study included data on all cancers, except skin, brain, lymphatic, hematologic and nonfatal prostate malignancies.
The researchers defined a healthy lifestyle pattern as never smoking or past smoking of less than 5 pack-years; alcohol abstention or moderate drinking (0-1 drinks per day for women and 1-2 drinks per day for men); a BMI of at least 18.5 but lower than 27.5; and weekly physical activity of at least 75 vigorous-intensity minutes or 150 moderate-intensity minutes.
The study included data from 89,571 women and 46,339 men. Participants who met all healthy lifestyle patterns (women, n = 16,531; men, n = 11,731) comprised the low-risk group; the remaining participants (women, = 73,040; men, n = 34,608) comprised the high-risk group.
The researchers calculated population-attributable risk (PAR) by comparing the incidence and mortality of total and major individual cancers between the low- and high-risk groups.
The incidence of total cancers per 100,000 people in the low- vs. high-risk groups was 463 vs. 618 in women and 283 vs. 425 men. These data equated to a PAR for overall cancer incidence of 25% (95% CI, 21-29) for women and 33% (95% CI, 28-38) for men. PARs were higher for cancer mortality among men (44%; 95% CI, 39-48) and women (48%; 95% CI, 44-53).
The highest PARs for individual cancer incidence occurred for lung cancer (women, 82%; men, 78%), followed by colorectal cancer (women, 29%; men, 20%), pancreatic cancer (women, 30%; men, 29%), bladder cancer (women, 36%; men, 44%), kidney cancer (women, 36%; men, 4%), oral cavity and oropharynx cancer (women, 16%; men, 38%), liver cancer (women, 27%; men, 32%) and esophageal cancer (women, 62%; men, 66%).
PARs for death were comparable to PARs for incidence, with the exception of higher PARs for mortality from breast cancer (12%), endometrial cancer (49%), kidney cancer in men (48%), and oral cavity and oropharynx cancer (women, 75%; men, 57%).
Researchers then assessed PAR at the national scale, by comparing the low-risk group to the general non-Hispanic white U.S. population. PARs were substantially higher in this comparison for cancer incidence (women, 41%; men, 63%) and mortality (women, 59%; men, 67%). This increase also was observed for specific cancers, such as breast cancer (incidence, 15%; mortality, 45%) and colorectal cancer (incidence, 50%; mortality, 60%).
Graham A. Colditz
Study limitations included the inclusion of data from non-Hispanic white individuals only and the potential bias introduced by studying health care professionals, who may be more health conscious than the general population.
“These findings reinforce the predominant importance of lifestyle factors in determining cancer risk,” Song and Giovannucci wrote. “Therefore, primary prevention should remain a priority for cancer control.”
It remains to be seen how these findings will be used to control cancer, Graham A. Colditz, MD, DrPH, MPH, deputy director of the Institute for Public Health at Washington University School of Medicine, and Siobhan Sutcliffe, PhD, MHS, ScM, associate professor of surgery at Washington University School of Medicine, wrote in an accompanying editorial.
“Our challenge now is to act on this knowledge,” Colditz and Sutcliffe wrote. “We have a history of long delays from discovery to translating knowledge to practice. 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.” – by Cameron Kelsall
References:
Colditz GA and Sutcliffe S. JAMA Oncol. 2016;doi:10.1001/jamaoncol.2016.0889.
Song M and Giovannucci E. JAMA Oncol. 2016;doi:10.1001/jamaoncol.2016.0843.
Tomasetti C and Vogelstein B. Science. 2015;doi:10.1126/science.1260825.
Disclosure: Song and Giovannucci report no relevant financial disclosures. Colditz and Sutcliffe report no relevant financial disclosures.
Perspective
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Michael J. Hall, MD, MS
This study by Song and colleagues quantifies the benefits of healthy lifestyle on cancer risk. In the study, members of two large cohorts of over 85,000 women and 45,000 men were placed into two risk groups based on self-reported lifestyle risk factors (smoking, drinking and exercise) and one biometric measure (BMI > 18.5 but < 27.5 vs. other).
Not surprisingly, those individuals who reported the healthiest lifestyle that is, those who had four out of four of the healthy lifestyle factors developed fewer cancers.
However, the researchers went a step further to consider the impact of healthy lifestyle on overall cancer incidence and death in the population through the calculation of population attributable risk (PAR). Via PAR, they estimated that 20% to 40% of cancer cases and approximately 50% of cancer deaths could be prevented by elimination of all unhealthy lifestyle risk factors from the population.
The goal of this study, and its overall importance, is not to prescribe unachievable benchmarks of good behavior to the general population. The importance here, rather, is the insight it provides on the incremental and overall combined impact that unhealthy lifestyle risk factors have on cancer incidence and mortality in the general population. Although perfection is difficult, if not impossible, to achieve in the realm of health behavior, we can appreciate from these data that 50% of cancers appear to be preventable via methods to mitigate unhealthy behaviors such as excessive alcohol consumption and smoking and to encourage good behaviors like weight/body size control and regular exercise.
For health policy experts and major funding agencies like the NIH and NCI, these data serve as an important reminder that although perhaps less sexy than laboratory science and developmental therapeutics, research funding to develop and test innovative population-based health behavioral interventions must remain a high priority in this country when one considers the magnitude of the potential to reduce cancer burden through health behavior modification.
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