An international team of researchers have linked excess weight and obesity to 8 additional types of cancer. The findings, published in the New England Journal of Medicine, were made after reviewing over 1,000 studies on weight and cancer risk.
The analysis was conducted by the World Health Organization’s International Agency for Cancer on Research (IARC) in France using data from both men and women, and from several geographic regions around the world. The team found that excess weight increases the risk of specific cancers —e.g. stomach, liver, gallbladder, pancreas, ovary, meningioma (a type of brain tumor), thyroid cancer and the blood cancer multiple myeloma — and managing weight can reduce the risk.
"The burden of cancer due to being overweight or obese is more extensive than what has been assumed," said cancer prevention expert Graham Colditz and chair of the IARC Working Group in a statement. "Many of the newly identified cancers linked to excess weight haven't been on people's radar screens as having a weight component."
Overall, the team found a positive correlation with higher body-mass index (BMI) and greater cancer list. As for why obesity spikes a person’s risk of cancer, the team notes there could be a variety of factors at play. For example, weight gain leads to an increase of hormones like estrogen, testosterone and insulin, which can boost cancer growth.
The researchers previously linked obesity to five types of cancer: colon, esophagus, kidney, breast and uterus. Combining their previous and current findings concludes that excess weight is associated with 13 forms of cancer.
"Lifestyle factors such as eating a healthy diet, maintaining a healthy weight and exercising, in addition to not smoking, can have a significant impact on reducing cancer risk," Colditz said. "Public health efforts to combat cancer should focus on these things that people have some control over."
Current estimates project that 640 million adults and 110 million children are obese. In the U.S., a third of adults and children are said to suffer from obesity. Together, the 13 cancers constitute 42 percent of new cancer cases. These figures, coupled with the IARC findings, highlight the importance of public health campaigns focusing on weight management.
"Significant numbers of the U.S. and the world's population are overweight," Colditz said. "This is another wake-up call. It's time to take our health and our diets seriously."
For those who struggle with losing weight, Colditz suggests not focusing on losing weight. "Rather than getting discouraged and giving up, those struggling to take off weight could instead focus on avoiding more weight gain,” said Colditz.
According to Elizabeth A. Platz, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, there is a big takeaway for women as well. “The strongest association they found is with uterine cancer,” said Platz to The New York Times. “And postmenopausal breast cancer is also connected to obesity, especially estrogen receptor positive cancer. These are important messages that women need to hear.”