An analysis of more than 1000 studies suggests multiple myeloma (MM) and 12 other cancers are associated with excess weight.
The data suggest that limiting weight gain over time could help reduce a person’s risk of developing these cancers.
A working group convened by the International Agency for Research on Cancer (IARC) conducted this analysis and reported the results in NEJM.
“The burden of cancer due to being overweight or obese is more extensive than what has been assumed,” said Graham Colditz, MD, DrPH, who chaired the IARC working group.
“Many of the newly identified cancers linked to excess weight haven’t been on people’s radar screens as having a weight component.”
In 2002, an IARC working group reported finding sufficient evidence linking excess weight to higher risks of colon, esophageal, kidney, breast, and uterine cancers.
Now, another IARC working group has found evidence linking excess weight and additional cancers.
The group reviewed more than 1000 epidemiologic studies. Most of the studies provided cancer risk estimates for adult body mass index (BMI), although some provided estimates for BMI or body shape in childhood/adolescence, changes in BMI or weight over time, or other indicators of adiposity.
The IARC working group reported the relative risk (RR) of developing various cancers for the highest BMI category evaluated, versus a normal BMI.
The group said there was sufficient evidence linking excess weight to the following cancers: adenocarcinoma (RR=4.8), gastric cardia (RR=1.8), colon and rectal cancer (RR=1.3), liver cancer (RR=1.8), gallbladder cancer (RR=1.3), pancreatic cancer (RR=1.5), postmenopausal breast cancer (RR=1.1), corpus uteri (RR=7.1), ovarian cancer (RR=1.1), renal cell cancer (RR=1.8), meningioma (RR=1.5), thyroid cancer (RR=1.1), and MM (RR=1.5).
Looking more closely at MM, the RR was 1.2 for adults who were overweight (BMI 25-29.9), 1.2 for those with class 1 obesity (BMI 30-34.9), and 1.5 for those with class 2 or 3 obesity (BMI 35-40+).
For most of the cancers, there was positive dose-response relationship; in other words, the higher the BMI, the greater the cancer risk.
In addition, the cancer risks associated with excess weight were similar for men and women and were consistent across geographic regions—North America, Europe, Asia, and the Middle East—where data were available.
“Significant numbers of the US and the world’s population are overweight,” Dr Colditz noted. “This is another wake-up call. It’s time to take our health and our diets seriously.”
Dr Colditz conceded that losing weight can be difficult. Therefore, he recommended that people who struggle with weight loss should focus on avoiding weight gain to reduce their risk of developing certain cancers.
