Risk for 4 cancers goes up the longer a woman is overweight

A longitudinal study of almost 74,000 postmenopausal women found that for every decade a woman is overweight, her risk of obesity-related cancers is likely shoot up by 7 percent. But the findings do not prove excess weight causes these cancers.

Duration and extent of overweight and obesity in adulthood have been linked with a significantly increased risk of all obesity-related cancers, according to an analysis of Women’s Health Initiative (WHI) data. The risk was increased for colon and postmenopausal breast cancers but highest for endometrial cancer and kidney cancer.

Over 6,000 cancers were diagnosed during the 12.6-year mean follow-up. No link was seen between time spent overweight and rectal, liver, gallbladder, pancreatic, ovarian or thyroid cancer. “By studying whether and how overweight and obesity affect cancer risk, we hope to be able to design ways to prevent cancer”. “If we manage to raise awareness among people and health practitioners that obesity is a risk factor for several diseases, not only cancer, this would be a great success”, lead author Melina Arnold, PhD, of the International Agency for Research on Cancer, Lyon, France, told MedPage Today in an email.

“We wanted to answer questions like “Does it matter how many years you have been obese during your life?’ and “Does the degree of overweight and obesity play a role in this?’ In epidemiology we call this ‘dose-response relationship” or the ‘impact of cumulative exposure”.

Why is there a link between obesity and cancer? About two thirds of women were overweight or obese at some point during adulthood. 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. “This is why it is hard to make a general statement about how much overall cancer risk increases per year of overweight or obesity”.

In secondary analyses, a priori interactions were assessed by stratifying by postmenopausal hormone use, hysterectomy and/or oophorectomy, ethnicity, diabetes, and smoking status.

Statistical analyses included adjustments for these factors.

A longitudinal study featuring almost 74,000 USA women has found that the longer a woman has been overweight or obese during her adult life, the higher her risk of developing cancer.

In the study, 439 overweight/obese postmenopausal women who did not have cancer were randomized to 1 of 4 groups: follow a diet that restricted calories and fat, participate in aerobic exercise 5 days a week, combine diet and exercise, and no intervention (control). The researchers while assessing the data have especially focused on women’s body mass index measurement, physical activity, diet, smoking, hormone use and cancer.

Arnold told MedPage Today, “Given a similar overweight prevalence in this cohort of women when compared to the general USA population, we believe that our findings are generalizable to the female USA elderly population and potentially to other high-income countries experiencing similar levels of overweight and obesity”. “Excess fat tissue causes an overproduction of several blood and tissue factors that can initiate or promote growth of tumors, such as estrogens, testosterone, inflammation, insulin, and factors that cause growth of blood vessels that can feed tumors”, said Dr. Anne McTiernan, a cancer prevention researcher at the Fred Hutchinson Cancer Research Center in Seattle, who was not involved in the new study.