High body mass index (BMI) has become the leading risk factor of disease burden in high-income countries. While recent studies have suggested that the risk of cancer related to obesity is mediated by time, insights into the dose-response relationship and the cumulative impact of overweight and obesity during the life course on cancer risk remain scarce. To our knowledge, this study is the first to assess the impact of adulthood overweight and obesity duration on the risk of cancer in a large cohort of postmenopausal women.
Methods and Findings
Participants from the observational study of the Women’s Health Initiative (WHI) with BMI information from at least three occasions during follow-up, free of cancer at baseline, and with complete covariate information were included (n = 73,913). Trajectories of BMI across ages were estimated using a quadratic growth model; overweight duration (BMI ≥ 25 kg/m2), obesity duration (BMI ≥ 30 kg/m2), and weighted cumulative overweight and obese years, which take into account the degree of overweight and obesity over time (a measure similar to pack-years of cigarette smoking), were calculated using predicted BMIs. Cox proportional hazard models were applied to determine the cancer risk associated with overweight and obesity duration. In secondary analyses, the influence of important effect modifiers and confounders, such as smoking status, postmenopausal hormone use, and ethnicity, was assessed. A longer duration of overweight was significantly associated with the incidence of all obesity-related cancers (hazard ratio [HR] per 10-y increment: 1.07, 95% CI 1.06–1.09). For postmenopausal breast and endometrial cancer, every 10-y increase in adulthood overweight duration was associated with a 5% and 17% increase in risk, respectively. On adjusting for intensity of overweight, these figures rose to 8% and 37%, respectively. Risks of postmenopausal breast and endometrial cancer related to overweight duration were much more pronounced in women who never used postmenopausal hormones. This study has limitations because some of the anthropometric information was obtained from retrospective self-reports. Furthermore, data from longitudinal studies with long-term follow-up and repeated anthropometric measures are typically subject to missing data at various time points, which was also the case in this study. Yet, this limitation was partially overcome by using growth curve models, which enabled us to impute data at missing time points for each participant.
In summary, this study showed that a longer duration of overweight and obesity is associated with an increased risk of developing several forms of cancer. Furthermore, the degree of overweight experienced during adulthood seemed to play an important role in the risk of developing cancer, especially for endometrial cancer. Although the observational nature of our study precludes inferring causality or making clinical recommendations, our findings suggest that reducing overweight duration in adulthood could reduce cancer risk and that obesity prevention is important from early onset. If this is true, health care teams should recognize the potential of obesity management in cancer prevention and that excess body weight in women is important to manage regardless of the age of the patient.
In a longitudinal study, Melina Arnold and colleagues assess the relationship between adulthood overweight and obesity duration and cancer risks in postmenopausal women.
Why Was This Study Done?
Excess weight has become the leading risk factor for disease burden in high-income countries and has been offsetting or surpassing the decreasing disease burden attributable to tobacco smoking. Excess weight has been linked to the development of several types of cancer.
To date, most studies exploring the relationship between excess weight and cancer risk looked at cross-sectional exposure information on overweight and obesity, i.e., height and weight measured at one point in time. Insights into the dose-response relationship of the cumulative impact of overweight and obesity during the life course on cancer risk remain scarce.
What Did the Researchers Do and Find?
This study examined how the timing, duration, and intensity of overweight and obesity during adulthood impacts on cancer risk, taking into account important information on other factors related to obesity, such as physical activity, diet, smoking, hormone use, and diabetes history.
A total of 73,913 women were included in the study, and 6,301 obesity-related cancers were diagnosed during a mean follow-up of 12.6 y. About two-thirds of all included women were ever overweight or obese during adulthood.
The study found that being overweight for a longer duration during adulthood significantly increased the incidence of all obesity-related cancers by 7% (for every ten-year increase in adulthood overweight duration), of postmenopausal breast cancer by 5%, and of endometrial cancer by 17%. After adjusting for the intensity of overweight (that is, how overweight individuals were), these figures rose to 8% for postmenopausal breast cancer and 37% for endometrial cancer (for every ten years spent with body mass index ten units above normal weight).
What Do These Findings Mean?
How much of their adult lives women are overweight and how overweight they are play important roles in cancer risk. This finding highlights the importance of obesity prevention at all ages and from early onset.