It’s no secret that cancer is the second leading cause of death for women in the U.S., accounting for approximately 275,000 deaths per year. This causes not only a tremendous physical and emotional toll, but also places a significant economic burden on society. Approximately $90 billion is spent each year on the direct costs of cancer such as medication, hospital, physician, and nursing services.
Our health behaviors play a significant role in determining our risk of developing different types of cancer. It has long been known that there are many risk factors for cancer that can be modified by changes in health behaviors. These include tobacco use, poor diet, moderate–to-high alcohol intake, as well as exposure to carcinogens in the environment and/or at work. More recently, obesity and sedentary lifestyle have been shown to be significantly associated with cancer death in women. Thus, we thought it would be of great interest to examine various combinations of cardiorespiratory fitness (CRF) level and obesity measures on risk of cancer death.
A sample of 14,256 women completed a comprehensive physical examination at the Cooper Clinic. All women were cancer free at baseline. The exam included a maximal treadmill exercise test to measure CRF, while measures of height and weight were used to determine body mass index (BMI)*. Women were divided into low, moderate, and high CRF categories based on their treadmill time and age, and were also divided into normal weight, overweight, and obese categories based on their BMI. The sample was then followed for an average of 15 years, during which 250 cancer deaths occurred. Breast, lung, and ovarian cancer accounted for 52% of these cancer deaths. In our analyses, we carefully controlled for factors such as smoking and age that might ‘muddy the waters.’ First, we examined the relationships between CRF, BMI, and cancer death rates separately; these results are shown in Figures 1 and 2 below.
In Figure 1, we see a strong association between CRF and the rate of cancer death. The rates were 7.9, 5.5, and 2.9 deaths/10,000 person-years** in low, moderate, and high CRF categories respectively.
In Figure 2, we see a strong association between BMI and the rate of cancer death. The rates were 4.6, 5.7, and 8.8 deaths /10,000 person-years in normal weight, overweight, and obese BMI categories respectively.
Lastly, we examined different combinations of CRF and BMI on risk of cancer death. Moderate and highly fit women were combined into a ‘Fit’ category. These results are found in Figure 3 below.
Within each BMI category, fit women had substantially lower cancer death rates compared to unfit women. The sample size was quite small for obese women who were fit; therefore those results (0.3 cancer deaths per 10,000 person-years) need to be interpreted with caution.
These results suggest that CRF is a stronger predictor of cancer death in women than BMI. Women in all BMI categories are urged to achieve at least a moderate level of CRF in order to decrease their risk of cancer death. Such levels of CRF are attainable for most women who meet or exceed the minimal public health guidelines for physical activity (perform at least 150 minutes of moderate intensity aerobic activity per week, and perform resistance training at least twice per week). Not using tobacco, limiting alcohol intake, consuming more plant-based foods, and consuming less red and processed meat can decrease this risk much further!
*BMI is calculated as follows: BMI = body weight x 703 / height in inches2. Normal weight is a BMI of 18.5-24.9 kg/m2, overweight is a BMI of 25.0-29.9 kg/m2, and obesity is a BMI of 30 kg/m2 or higher.
**Death rates are often reported as number of deaths per 10,000 person-years. For example, if 1000 people are followed for 10 years, then we have 1000 x 10 = 10,000 person-years of data.
Farrell, S. W., Finley, C., E., McAuley, P. A., & Frierson, G. M. (2011). Cardiorespiratory fitness, different measures of adiposity and total cancer mortality in women. Obesity, 19, 2261-2267. doi:10.1038/oby.2010.345