A new study on postmenopausal women reveals that the duration of having a high body mass index (BMI) is linked to a higher risk of developing several types of cancer, from breast to endometrial.
The study, which was published in the journal PLOS Medicine, is the first to explore the relationship between overweight duration and cancer risk in a large cohort of women, according to Melina Arnold, a scientist at the World Health Organization’s International Agency for Research on Cancer (IARC) and lead author of the study.
“Given the result from previous studies supporting the overall link between obesity and cancer, our results are in line with what we know about this relationship,” Arnold said. “Yet it adds to current scientific evidence by suggesting that there seems to be a cumulative effect of obesity on cancer risk.”
The researchers analysed data on 73,913 women across the United States using information from the long-term national health study Women’s Health Initiative.
They took a close look at the women’s BMI measurements, diet, physical activity, smoking habits, hormone use, and cancer and diabetes history.
BMI is often used as a screening tool for being overweight or obese, as a measurement of 25 to 30 falls within the overweight range and 30 or higher falls within the obese range, according to the Centers for Disease Control and Prevention (CDC).
Over the 12-year study period, about 6,301 obesity-related cancers were diagnosed among the women.
The research team found that for every 10 years the women were overweight during adulthood, their risk for all obesity-related cancers increased by seven percent.
Meanwhile, the risk for postmenopausal breast cancer went up by five percent, and the risk for endometrial cancer increased by a whopping 17 percent.
The amount that the women were overweight also played a significant role in their cancer risk.
According to Arnold: “This is biologically plausible, as earlier and longer periods of overweight and obesity have been found to increase the risk and severity of hypertension, insulin resistance, chronic inflammation, DNA damage and changes in hormone metabolism, which are all key mechanisms increasing also the risk of cancer.”
She added that more research is needed to determine whether the findings are still applicable for women who may lose weight for a period of time and then gain it back.
“We also showed in our study that the risk to develop these cancers is not only dependent on overweight duration itself but also on the degree of overweight over time,” Arnold said.
“This is why it is difficult to make a general statement about how much overall cancer risk increases per year of overweight or obesity.”
Hoda Anton-Culver, professor and chairwoman of epidemiology at the University of California, Irvine and a co-author of the study, said she and her colleagues plan to further explore this topic.
So why is there a link between obesity and cancer?
“Excess fat tissue causes an overproduction of several blood and tissue factors that can initiate or promote growth of tumours, such as oestrogens, testosterone, inflammation, insulin, and factors that cause growth of blood vessels that can feed tumours,” said Dr Anne McTiernan, a cancer prevention researcher at the Fred Hutchinson Cancer Research Center in Seattle.
“Both men and women have increased risks for several cancers if they are overweight or obese,” added McTiernan, who was not involved in the new study.