Research has linked both body weight and exercise to survival in various cancers. For example, a review of 16 observational studies of populations of breast cancer patients showed that women who engaged in any kind of physical activity before their cancer diagnosis had approximately a 20% lower risk of dying from breast cancer or other causes. Physical activity after diagnosis had about the same effect. For colon cancer, an increase in exercise of about 30 minutes, 5 days a week, reduced cancer mortality by 38%. And an observational study of obese women – those whose body mass index was over 30 – demonstrated an increased risk of dying from lung, colon and breast cancer that was 3-4 times that of normal weight women (body mass index of 20-25).
Ovarian cancer is the most fatal of the gynecologic cancers, and affects over 20,000 women a year in the United States. Do exercise and body weight affect outcomes in this cancer? Some previous studies suggested that this might be the case, but these studies were generally too small to draw accurate conclusions.
To address this question, a national group of researchers used data that was collected during the course of a major study of women’s health, the Women’s Health Initiative. This study collected data from healthy women, and then observed them for several years during trials of hormone therapy, diet modification and calcium and vitamin D supplementation. About 900 of the more than 161,000 women in the study were diagnosed with ovarian cancer after the start of the study. Of these, 600 had sufficient data to be included in an analysis of effects of exercise and body mass index on breast cancer. Ovarian cancer patients in the study were diagnosed an average of 7 years after they started the study.
At the start of the study, data were collected on height, weight and physical activity. Physical activity was classified as walking, moderate-intensity recreational activity and vigorous-intensity recreational activity. The researchers calculated body mass index from height and weight data (a calculator is available at http://www.bmi-calculator.net/). They then calculated the risk of mortality due to ovarian cancer, and overall risk of mortality from all causes. The analysis took into account potentially modifying variables such as use of hormone therapy, smoking, history of diabetes and participation in diet modification or calcium-vitamin D supplementation.
This study found no association between BMI measured in the study and either overall mortality or mortality due to ovarian cancer. Another publication reviewed ovarian cancer and obesity, and included studies in which BMI was measured at the time of diagnosis or chemotherapy. That publication found that obese (BMI over 30) ovarian cancer patients had a 17% higher mortality than those of normal weight. It’s not clear why the impact of BMI measured at the time of diagnosis is different from BMI measured an average of 7 years before diagnosis. Perhaps the difference arises because of the typically aggressive and fast-moving nature of ovarian cancer, which might grow quickly over just a few years, and thus be more heavily influenced by the conditions in the body just before diagnosis than a cancer like breast cancer, which takes many years to grow. The lack of influence of BMI on overall mortality (mortality from all causes) is similar to results seen in some other studies, which find a “U” shaped relationship between BMI and mortality, in which high mortality is seen in both underweight and obese people, while both those with normal weight and those who are overweight, but not obese, have lower mortality.
Researchers found that patients reporting moderate physical activity did not have better overall or ovarian cancer mortality than those who reported no physical activity. However, when they contrasted those who reported any kind of vigorous physical activity with all the other patients (i.e., those who had no physical activity and those who had moderate physical activity), they found that the vigorous activity group had 24% lower overall mortality and a 26% lower ovarian cancer mortality. This result is different than that found in some other cancers, such as breast cancer, in which moderate physical activity was linked to better outcomes. It seems to take really vigorous physical activity prior to diagnosis in order to have an impact on the course of this aggressive disease.
What kinds of activity are classified as vigorous and moderate? Moderate physical activity includes activities like brisk walking, heavy cleaning, moderate bike riding, badminton and doubles tennis. Vigorous physical activity, on the other hand, includes hiking, jogging, carrying heavy loads, fast bicycling, basketball, soccer and singles tennis.
In evaluating this study, it’s important for ovarian cancer patients, as well as other readers, to remember that for the time being we don’t have proof from randomized, controlled trials (considered the “gold standard” in research) that taking up either moderate or vigorous physical activity after you are diagnosed will improve your outcome. All we have so far are results of observational studies like this one, that look at existing exercise habits of patients and link them to mortality or disease outcomes. The studies in which cancer patients are randomly assigned to do exercise, and then monitored for their survival are currently underway. These are the studies that will be needed to prove that exercise improves ovarian cancer survival.
So we can’t know for certain that ovarian cancer patients who take up vigorous exercise are going to do better than those who exercise moderately. But what we do observe from exercise trials to date is that exercise improves fatigue, functioning and quality of life in multiple types of cancer. For ovarian cancer specifically, a study in which stage 3 and 4 ovarian cancer patients were instructed to start walking, based on an individualized assessment of their physical condition. Women who integrated walking into their daily activities experienced improvements in physical functioning, physical symptoms, physical well-being and quality of life! Therefore, whether or not walking or other exercise will definitely improve survival, we are all in favor of healthful interventions that improve quality of life and daily functioning for cancer patients, and would encourage all patients to undertake exercise programs individualized to their particular physical abilities and medical conditions.