More than a decade ago, after conducting a comprehensive review of the scientific evidence at that time, an international team of researchers reported that excess weight was linked to higher risks of five cancers: colon, esophagus, kidney, breast and uterus.
That same group of researchers — convened by the World Health Organization’s International Agency for Cancer on Research (IARC) — now says the list needs to be expanded.
In a new analysis of the existing evidence, published Thursday in the New England Journal of Medicine (NEJM), the researchers identify eight additional cancers linked to excess weight and obesity: stomach, liver, gall bladder, pancreas, ovary, thyroid, meningioma (a type of brain tumor) and multiple myeloma (a type of blood cancer).
“The burden of cancer due to being overweight or obese is more extensive than what has been assumed,” said Dr. Graham Colditz, a cancer-prevention specialist at the Washington University School of Medicine in St. Louis and chair of the IARC research team, in a released statement. “Many of the newly identified cancers linked to excess weight haven’t been on people’s radar screens as having a weight component.”
A global problem
Obesity is generally determined by body mass index (BMI). Overweight is defined as a BMI of 25.0 to 29.9, and obesity as a BMI of 30 or more. (Yes, the BMI method of determining a healthy weight is not accurate in every case, but it’s generally considered “a good proxy for assessing overall body fatness,” as the authors of the new analysis point out.)
The rapidity with which the world is becoming obese is stunning. An estimated 640 million adults and 110 million children are now obese. That’s six times as many adults and twice as many children as four decades ago.
In fact, more people today are overweight or obese than are underweight.
In the United States, 38 percent of adults aged 20 and older are considered obese, according to the Centers for Disease Control and Prevention (CDC).
Last year, the U.S. passed a distressing milestone: More Americans are now obese than overweight.
The toll on health is enormous. Globally, about 4.5 million deaths are caused by overweight and obesity each year, according to a study published earlier this year in the journal Cancer Epidemiology.
Many of those are cancer deaths. The Cancer Epidemiology study estimated, for example, that 9 percent of cancers developed among women in North America, Europe and the Middle East are linked to obesity.
Up to 13 cancers
In the new IARC analysis, which involved examining more than 1,000 relevant epidemiologic studies, the highest risks associated with being overweight or obese were for uterine cancer and esophageal cancer (specifically, adenocarcinoma, which begins in the mucus-producing glandular cells of the esophagus).
When compared with people of normal weight, those with the highest BMI (40 or greater) were almost five times more likely to develop uterine cancer and almost seven times more likely to develop esophagus adenocarcinoma.
For people in the highest BMI category, the increased relative risk for the other 11 cancers ranged from 10 percent (for multiple myeloma and postmenopausal breast cancer) to 80 percent higher (for cancers of the stomach, kidney and liver).
The analysis also found that the higher the BMI, the greater the risk — for some cancers, at least. For example, compared with normal-weight women, those with a BMI of 25 to 25.9 had a 50 percent higher relative risk for endometrial (uterine) cancer. That risk more than doubled when the BMI was between 30 and 34.9, and it more than quadrupled when it reached the 35 to 39.9 range. And for women with a BMI of 40 or greater, the risk climbed seven-fold.
Another wake-up call
The studies involved in this analysis were mostly observational ones, which means they cannot prove a direct link between excess weight and the development of cancer.
The authors of the current analysis point out, however, that excess fat is associated with an overproduction of various hormones, such as estrogen, testosterone and insulin, as well as with chronic inflammation — factors that may help explain its link to cancer.
But plenty of people who aren’t overweight or obese develop cancer, and many obese people never get the disease. So this study shouldn’t be used as way of “blaming” overweight people with cancer for their illnesses.
Still, as Colditz says: “This is another wake-up call. It’s time to take our health and our diet seriously.”
FYI: You’ll find an abstract of the IARC report on the NEJM website, but the full report is, unfortunately, behind a paywall.