A new systematic review and meta-analysis confirms an association between obesity and bladder cancer. Pre-obese individuals also may be at risk.
For the meta-analysis, Yong-Bing Xiang, MD, and colleagues from the Shanghai Cancer Institute at Renji Hospital in China, pooled results from 15 cohort studies published by September 2014 from North America, Europe (including Scandinavia), Asia, and Australia. Among 14 million people, 38,072 bladder cancer cases were identified.
Compared with normal-weight individuals (body mass index [BMI] 18.50–24.99 kg/m2), preobese and obese individuals (BMI 25.00–29.99 and 30 or greater, respectively) had a 7% and 10% increased risk of bladder cancer, respectively, the researchers reported in PLOS One.
Researchers observed a linear relationship between body mass index (BMI) and bladder cancer risk. For each 5 kg/m2 increase in BMI, there was a 4.2% hike in bladder cancer risk.
The findings update and expand a 2013 meta-analysis that reached a similar conclusion. A shortcoming of that study was it did not address confounders.
Investigators in the current study adjusted for smoking and found no meaningful differences. They also examined other possible confounders. Studies that adjusted for physical activity, alcohol consumption, and family history of cancer, for example, actually showed stronger associations.
The researchers presented several theories for how obesity might promote carcinogenesis. Elevated insulin production, which is linked to obesity, might fuel tumor growth. In addition, obesity might promote chronic low-grade inflammation, causing disruptions in levels of cytokines and adipokines that promote cancer.
Given the rising rates of pre-obesity and obesity worldwide, “more in-depth studies are warranted to disentangle the roles of the biological mechanisms involved in obesity-related carcinogenesis,” the researchers concluded.