OBESITY AND CANCER RISK

A longer duration of being overweight during adulthood significantly increased the incidence of all cancers that are associated with obesity, a new study in postmenopausal women has concluded. The large population-based study was publishedAugust 16 in PLoS Medicine.

"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," write the authors, led by Melina Arnold, PhD, from the International Agency for Research on Cancer, Lyons, France.

Dr Arnold and colleagues found that for every 10 years of being overweight as an adult, there was an associated 7% increase in the risk for all obesity-related cancers.

The risk was highest for endometrial cancer (17%) and kidney cancer (16%).

For breast cancer, the increased risk was 5%, but no significant associations were found for rectal, liver, gallbladder, pancreatic, ovarian, and thyroid cancer.

When the authors took into account the degree of excess weight over time, the risks were further increased, and there were "clear dose-response relationships," they note.

Again, the risk was highest for endometrial cancer. For each additional decade spent with a body mass index (BMI) that was 10 units above normal weight, there was a 37% increase in the risk for endometrial cancer.

Overweight/obesity is also associated with an increased risk for other serious health conditions, including diabetes, stroke, and cardiovascular disease. While the authors in this study looked only at the impact on cancer, it may be likely that the duration and degree of obesity could also play into the risk for other illnesses, explained study coauthor Hoda Anton-Culver, PhD.

"We are looking at these chronic conditions as well," she told Medscape Medical News.

The study also looked only at women, so it is unclear whether these results could extrapolate to men as well. "Mechanistically we can extrapolate for some cancer sites, but quantitatively and to look at other cancer sites we should replicate the study in men," Dr Anton-Culver said.

The findings also help bring home the message that excess body weight can affect health. "I think the results provide strength and ammunition to the healthcare providers to counsel their patients, particularly those at high risk, and also to apply intervention programs for weight control in those who are overweight," said Dr Anton-Culver.

Study Details

The researchers used data from the huge American Women's Health Initiative (WHI) trial of postmenopausal women (aged 50 to 79 years at time of study enrollment).

For this analysis, the team focused on a cohort of 73,913 postmenopausal women.

During a mean follow-up of 12.6 years, 6301 obesity-related cancers were diagnosed.

About 40% (n = 29,770) of women in the cohort were never overweight during their adult life.

The remaining 60% (n = 44,143) were ever overweight; of this subgroup, almost half (n = 19,654) were also ever obese.

Women who were ever overweight were on average overweight for about 30 years, while those who were ever obese had been so for an average of 20 years.

The authors found that the risk of being diagnosed with an obesity-related cancer rose for every 10 years of being overweight (hazard ratio [HR], 1.07).

The association for obesity duration was even stronger for all cancers (multivariable-adjusted HR per 10-year increment, 1.10), as well as individually for colon, breast, endometrial, and kidney cancer; the HRs for every 10 years of being obese ranged from 1.07 for breast cancer to 1.23 for endometrial cancer.

In a discussion of the study, NHS Choices, the official website of the National Health Service in England, notes that the "study's size and use of BMI measurements over time mean it is likely to be more reliable than smaller studies, or those that look at BMI only at one time point."

Despite the study's limitations, NHS Choices writes that "the study is a serious attempt to quantify the risk that overweight and obesity contribute to cancer risk. Obesity levels have been rising in recent decades and figures from Public Health England show 65% of men and 58% of women in England were overweight or obese in 2014."

The WHI program is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health. Support for Dr Arnold's research came from the Department of Epidemiology in the School of Medicine and the Genetic Epidemiology Research Institute at the University of California, Irvine; the World Cancer Research Fund International; and the Union for International Cancer Control International Cancer Technology Transfer Fellowship. Coauthor Erin LeBlanc's institution has received grant funding from the National Institutes of Health, the Agency for Healthcare Research and Quality, Merck, Amgen, Bristol-Myers Squibb, and Astra Zeneca for her research work that is unrelated to the current study. The other authors have disclosed no relevant financial relationships.

PLoS Med. Published online August 16, 2016