An interesting study was undertaken in China and published online on 15th September 2021. The aim was to look at the potential link between alcohol consumption and bladder cancer risk, using various relevant studies from the past, which were searched for in several databases. The results were controversial.
Bladder cancer ranks as the tenth most commonly diagnosed cancer globally, with an estimated 549,000 new cases and 200,000 deaths annually. Men are, perhaps surprisingly, more frequently affected than women, with incidence and mortality rates approximately four times higher in men. Given the substantial societal burden of bladder cancer, identifying its risk factors is vital for reducing its high incidence and mortality rates. While cigarette smoking is the most significant known risk factor, contributing to about half of all cases, other environmental exposures, such as aromatic amines and industrial chemicals, have also been linked to the disease. The relationship between alcohol consumption and bladder cancer, however, remains a topic of ongoing debate.
A study published on 15th September, 2021, titled “Association Between Alcohol Consumption and Risk of Bladder Cancer: A Dose-Response Meta-Analysis of Prospective Cohort Studies” by Yongfeng Lao, Xiaolong Li, et al., aimed to shed light on this perplexing relationship. The objective of the study was to quantitatively investigate the association between alcohol consumption and the risk of bladder cancer, exploring whether a potential dose-response relationship exists.
To achieve this, the researchers conducted a meta-analysis of prospective cohort studies, which involved systematically locating relevant studies from various databases. They performed a categorical meta-analysis to assess risk estimates for any alcohol consumers versus non-drinkers, as well as different degrees of drinking (light, moderate, and heavy) versus none. Additionally, they employed two-stage generalised least-squares regression, restricted cubic spline, and fixed-effects dose-response models to explore both linear and nonlinear dose-response relationships.
The study included data from nine prospective cohort studies, encompassing a total of 1,971,396 individuals. Overall, the researchers did not observe a significant association between alcohol intake and the risk of bladder cancer in the entire population. However, a linear association was detected in those who consumed alcohol from liquor or spirits (P linear=0.02). Specifically, an increment of one drink per day was associated with a 9% increase in the risk of bladder cancer (RR=1.09; 95% CI: 1.01-1.17).
The findings also highlighted a significant risk for male drinkers. Alcohol consumption was found to be a risk factor for bladder cancer among males in a dose-independent manner (RR=1.23; 95% CI: 1.13-1.35; I2=3.7%). Despite this, no linear or nonlinear relationship was observed in the male subgroup, suggesting that the increased risk might not be directly proportional to the amount of alcohol consumed.
The conclusion drawn from this comprehensive analysis was that no significant association exists between alcohol consumption and bladder cancer risk in the general population. However, a linear dose-response relationship was identified for those consuming liquor or spirits. Additionally, alcohol appeared to elevate the risk of bladder cancer in males, although this increase was dose-independent.
These findings contribute to the ongoing discussion about the role of alcohol in bladder cancer risk. Previous studies have shown mixed results. For instance, a meta-analysis of ten cohort studies in Japan found no evidence of an association between alcohol drinking and bladder cancer risk among men and women. Conversely, another meta-analysis of case-control and cohort studies suggested that heavy alcohol consumption significantly increased the risk of bladder cancer in men and the Japanese population without significant statistical heterogeneity.
Further complicating the picture, a recent large cohort study indicated that high alcohol intake was associated with an increased risk of urothelial cell carcinoma (UCC) in men and smokers, potentially due to residual confounding by smoking. Some studies have suggested alternative explanations, such as the role of acetaldehyde, a metabolite of alcohol, in the development of bladder cancer. For example, Masaoka et al. found that moderate alcohol consumption among men with flushing was linked to an increased risk of bladder cancer, supporting the hypothesis that acetaldehyde plays a significant role. Additionally, a case-control study suggested that individuals with inactive ALDH2 alleles, which affect alcohol metabolism, showed an elevated risk of bladder cancer among alcohol drinkers.
Despite the numerous studies conducted over the past decades, the relationship between alcohol consumption and bladder cancer remains unresolved. The study by Lao, Li, and colleagues represents a systematic effort to explore this association on a global scale without regional restrictions. Their dose-response meta-analysis synthesises available prospective studies, offering valuable insights into the potential dose-response relationship in both the general and specific populations. However, more research is needed to fully understand the complex interaction between alcohol consumption and bladder cancer risk.
The original study can be found here:
