Cancer Risk Increases the Longer a Woman Is Overweight or Obese

A large observational study of participants in the Women’s Health Initiative (WHI) study found that the longer a woman is overweight or obese, the higher the risk of developing several forms of cancer. The study, published in PLoS Medicine, also concluded that the degree of overweight during adulthood appears to play an important role in the risk of developing cancer, especially endometrial cancer.

The investigators, led by Melina Arnold of the International Agency for Research on Cancer in Lyon, France, and colleagues, said the study differs from most others exploring the relationship between excess weight and cancer risk that measure height and weight at only one point in time.

“The finding highlights the importance of obesity prevention at all ages and from early onset,” the authors wrote, and added that this is the first attempt to assess the impact of adult overweight and obesity duration on the risk of cancer in a large cohort of postmenopausal women.

A total of 73,913 women were included in the study, with body mass index (BMI) information from at least 3 occasions during a mean follow-up of 12.6 years. Trajectories of BMI across all ages were estimated using a quadratic growth model; overweight duration, obesity duration, and weighted cumulative overweight and obese years were calculated. Cox proportional hazard models were applied to determine the cancer risk associated with overweight and obesity duration. The investigators examined how timing, duration, and intensity of overweight and obesity during adulthood affected cancer risk, taking into account other important factors related to obesity such as physical activity, diet, smoking, hormone use, and diabetes history.

During follow-up, 6301 obesity-related cancers were diagnosed. About two-thirds of all the women in the study were either overweight or obese during adulthood.

Being overweight for a longer duration of adulthood significantly increased the incidence of all obesity-related cancers by 7% (for every 10-year increase in adulthood overweight duration), of postmenopausal breast cancer by 5%, and of endometrial cancer by 17%. After adjusting for how overweight individuals were, the figures rose to 8% for postmenopausal breast cancer and 37% for endometrial cancer (for every 10 years spent with BMI 10 units above normal weight).

The researchers also observed that the risks of postmenopausal breast and endometrial cancer related to overweight and obesity duration were modified by postmenopausal hormone use and were largely attenuated or even eliminated among postmenopausal hormone users.

The results of the study suggest that reducing duration of being overweight in adulthood can reduce cancer risk and that obesity prevention is important from early onset.

“How much of their adult lives women are overweight and how overweight they are play important roles in cancer risk,” the authors concluded. “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 age of the patient.”