Childhood obesity tied to bladder cancer risk

A high body mass index (BMI) early in life is associated with an increased risk of bladder cancer, a Danish study suggests.

Bladder cancer is relatively rare but has an extremely high recurrence rate (up to 70 percent), greatly impacting quality of life and treatment costs. [Nature 2017;551:S34-S35; CA Cancer J Clin 2019;69:363-385; J Med Econ 2019;22:662-670] Given the long latency period of bladder cancer, a potential association between body size and bladder cancer may likely be traced early in life. [Epidemiol Rev 1981;3:203-229]

“[Our findings] suggest that the higher levels of overweight and obesity in children today may contribute to an increased burden of bladder cancer in [the] future,” said lead author Dr Kathrine Sorensen from the Centre for Clinical Research and Prevention at the Bispebjerg and Frederiksberg Hospital in Denmark, in a press release.

At age 13, BMI z-score was positively associated with bladder cancer (hazard ratio, 1.10, 95 percent confidence interval, 1.02–1.18). [Ann Hum Biol 2020;47:166-172]

To put this into perspective, a BMI z-score shift from 0 to 1 (from 42.5 to 48.4 kg) equates to a hazard of 1.10. This implies that, for two 13-year-old boys of average height (154.5 cm), the risk of developing bladder cancer is 10-percent higher in the heavier one, explained senior author Dr Jennifer Baker, also from the Bispebjerg and Frederiksberg Hospital.

“Since adipose tissue accrual takes time, it is likely that a high BMI in childhood increases the cumulative exposure to adiposity which may, in turn, increase risks of bladder cancer,” said the researchers. Potential drivers of this association include higher levels of insulin, adipokines, and inflammation, as well as increased bioavailability of insulin-like growth factors. [Nat Rev Cancer 2015;15:484-498]

The findings are in keeping with previous evidence reflecting an association between urothelial cancer (mostly bladder) and overweight male adolescents. [Obesity 2012;20:2445-2450] Together with the current results, these support the theory that size early in life may have an impact on bladder cancer risk, noted the researchers.

The study sample comprised 315,763 individuals (50 percent male) from the CSHRR*. At a median follow up of 35 years, 1,145 individuals (73 percent male) were diagnosed with bladder cancer.

Despite the large study sample and measurements of high validity used in the study, the lack of data on lifestyle factors (eg, smoking, occupation) and the European-dominant population may have limited the generalizability of the findings. The low fraction of bladder cancer cases among women may have also limited the power to detect the impact of gender, noted the researchers.

There is limited evidence regarding the potential link between adult adiposity and bladder cancer, hence the need for further research in this area. “[Although] the overall chance of developing the disease may be low … it comes with a significant personal and economic impact. Our study contributes to the understanding of how body size early in life may indicate a risk for bladder cancer,” said Sorensen.