Cancer is a leading cause of death and suffering across the globe. The causes of cancer are complex, and not always well understood. Some of the common explanations for cancer include genetic predispositions (inherited from parents), cellular mechanisms, lifestyle choices (like smoking), and environmental exposures (sunlight, chemicals). Many of the above factors are nonmodifiable, and therefore not in our control. However, lifestyle choices are an important modifiable risk factor for cancer.
Lifestyle choices can affect cancer risk. Many research studies have linked smoking, heavy alcohol use, lack of exercise and obesity to cancer. In a seminal paper published in JAMA Oncology journal in 2016, researchers at Harvard tried to figure out the number of cancer cases and deaths in the United States attributable to these lifestyle factors.
For this study, the researchers collected lifestyle data and health information from a large group of female nurses and male health professionals. Participants, who were primarily white, provided data from the 1980s through 2010.
Researchers divided participants into a low-risk group and a high-risk group. Low-risk participants had the following characteristics: they did not smoke; they did not drink alcohol in excess of one drink daily for women or two drinks daily for men; they were not underweight or obese (BMI 18.5-27.5); and they engaged in regular physical activity (75 minutes of vigorous intensity physical activity per week or 150 minutes of moderate intensity exercise per week). Participants not meeting the above criteria were categorized as high risk. The researchers collected information on cancer incidence and death directly from individuals and also from a national database. Most fatal cancers were included in the analysis.
The results were striking. The total incidence of cancer was significantly higher in the high-risk group. Calculations showed a Population Attributable Risk (PAR) of 25% in women and 33% in men. PAR of 25% and 33% in this context means that there is an excess 25% and 33% risk of cancer in women and men respectively, that can be attributed to lifestyle factors. In other words, if the high-risk lifestyle choices could be eliminated, the risk would drop by 25% and 33% respectively for women and men.
The link between cancer deaths and unhealthy lifestyle choices was even more striking. PAR for mortality was 48% in women and 44% in men. Again, the implications are very profound. The researchers concluded that roughly half of all cancer deaths were attributable to lifestyle factors. When compared to the average US population, these differences were even more marked. This difference was probably because the average US population has lifestyle factors which can be considered “riskier” than the high-risk group studied in this paper (nurses and health professionals). For example, PAR for breast cancer in women was 12% for the high-risk group but 45% for the average US population.
Certain cancers were more closely attributable to lifestyle factors than others. For example, approximately 80% to 90% of lung cancer deaths could be avoided by lifestyle modification, primarily smoking cessation. The impact of lifestyle on mortality was notable across many different cancers including breast cancer, colon cancer, liver cancer, pancreatic cancer, esophageal cancer, kidney cancer, bladder cancer, endometrial cancer, and ovarian cancer.
Based on this very well conducted trial, it would be reasonable to conclude that a large number of cancers and cancer deaths are preventable. Although many lifestyle choices can reduce the risk of cancer, the four important ones highlighted by this study are the following: quitting smoking, avoiding heavy alcohol consumption, maintaining ideal body weight and exercising regularly.
Reference: https://jamanetwork.com/journals/jamaoncology/fullarticle/2522371
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