Melinda Irwin, Ph.D., the Susan Dwight Bliss Professor of Epidemiology, researches lifestyle factors associated with a variety of cancers and also how these same lifestyle factors can improve odds of survival and recovery. She has some intriguing findings that have implications for many people who are either at risk for cancer or are going through cancer treatment.
How does higher body weight, low physical activity or poor diet cause cancer?
MI: Lifestyle factors may lower cancer risk or mortality by changing hormones, which in turn can impact a wide range of human processes. These include energy metabolism, cellular growth factors, steroid metabolism, inflammatory mediation, DNA repair and immune function. Scientists have found that high body weight, low physical activity and poor diet are associated with an increased incidence of 13 cancers, and an increased mortality of 14 cancers.
Lifestyle factors can also play a large role in treating cancer. At Yale, we are currently trying to find out if a diet and physical activity intervention improves adherence to cancer treatments in women who have breast cancer. We think that lifestyle behaviors prevent or lessen side effects, which can improve treatment compliance and, ultimately, improve survival. It is important to understand how these lifestyle factors affect cancer outcomes so that clinical care can be improved for patients with cancer.
With our ability to work from home and use our cell phones to communicate so extensively, many children and adults are more sedentary than ever before. What is more important, exercising at high levels or sitting less?
MI: Both are important. Still, some intriguing observational findings have shown that people who exercise once or twice per week have a similar lowered risk of mortality as compared with people exercising daily. The highest-risk group are people who are inactive, but even people who do less than the recommended amount of exercise had a similar lowered risk of mortality as those who exercise daily or just on the weekend. Even though this finding was from a pooled analysis of a number of prospective observational studies and not a randomized trial, the findings are intriguing and give the important message that doing something is better than nothing.
For some people, reducing sedentary time might be more feasible than finding time for a 30- to 60-minute exercise session. Given that 80 percent of adults do not do at least 2.5 hours a week of moderate-intensity exercise, which is the current recommended amount, and given that a lack of physical activity is linked to about $117 billion in annual health care costs and about 10 percent of premature mortality, finding feasible ways for people to lower their risk of cancer and other chronic diseases is important. To reduce sedentary time, a good approach is to monitor how many steps are taken each day. Most adults walk about 5,000 steps per day. Increasing steps by about 2,000 steps per day, which is about one mile, is an appropriate goal. Ultimately, we should strive to walk at least 10,000 steps per day.
What areas still need to be examined in lifestyle factors and cancer?
MI: Numerous gaps exist in our understanding of the relationship between weight, diet, exercise and cancer in certain populations, including patients with metastatic cancer, racial or ethnic minorities and older adults. Approximately two-thirds of cancer survivors are 65 years and older, and by 2040, older adults are projected to make up 75 percent of cancer survivors. Future research also must focus on how to implement lifestyle behavioral counseling into oncology practice, which in turn may have a large population-level impact.
Obesity prevention and treatment services have not been a part of oncology care. Given that lifestyle behavior counseling programs carry a tremendous potential to affect the length and quality of survival and prevent or control morbidity associated with cancer or its treatment, oncologists and primary care physicians should be encouraged to refer patients for counseling on weight management, nutrition and physical activity. At the Yale Cancer Center Survivorship Clinic, a multidisciplinary team of health care providers counsel patients on these lifestyle behaviors.