Joint effects of alcohol use, smoking and body mass index as an explanation for the alcohol harm paradox: causal mediation analysis of eight cohort studies

Abstract

Background and aims Lower socio‐economic status (SES) is associated with higher alcohol‐related harm despite lower levels of alcohol use. Differential vulnerability due to joint effects of behavioural risk factors is one potential explanation for this ‘alcohol harm paradox’. We analysed to what extent socio‐economic inequalities in alcohol‐mortality are mediated by alcohol, smoking and body mass index (BMI), and their joint effects with each other and with SES. Design Cohort study of eight health examination surveys (1978–2007) linked to mortality data. Setting Finland. Participants A total of 53 632 Finnish residents aged 25+ years. Measurements The primary outcome was alcohol‐attributable mortality. We used income as an indicator of SES. We assessed the joint effects between income and mediators (alcohol use, smoking and BMI) and between the mediators, adjusting for socio‐demographic indicators. We used causal mediation analysis to calculate the total, direct, indirect and mediated interactive effects using Aalen's additive hazards models. Findings During 1 085 839 person‐years of follow‐up, we identified 865 alcohol‐attributable deaths. We found joint effects for income and alcohol use and income and smoking, resulting in 46.8 and 11.4 extra deaths due to the interaction per 10 000 person‐years. No interactions were observed for income and BMI or between alcohol and other mediators. The lowest compared with the highest income quintile was associated with 5.5 additional alcohol deaths per 10 000 person‐years (95% confidence interval = 3.7, 7.3) after adjusting for confounders. The proportion mediated by alcohol use was negative (−69.3%), consistent with the alcohol harm paradox. The proportion mediated by smoking and BMI and their additive interactions with income explained 18.1% of the total effect of income on alcohol‐attributable mortality. Conclusions People of lower socio‐economic status appear to be more vulnerable to the effects of alcohol use and smoking on alcohol‐attributable mortality. Behavioural risk factors and their joint effects with income may explain part of the alcohol harm paradox.

The dose-response relationship between socioeconomic deprivation and alcohol-attributable mortality risk—a systematic review and meta-analysis

“…Given that people of low SES tend to experience greater alcohol-related harm than those of high SES, even when the amount of alcohol consumption is the same or less than for individuals of high SES (i.e., the so-called alcohol-harm paradox) [ 7 , 8 ], it would have been ideal if we could have controlled for alcohol use in the included point estimates. However, this was not possible.…”

“…A systematic review and meta-analysis found that the relative socioeconomic inequalities in mortality were about 1.5 to two times higher for alcohol-attributable mortality, compared to socioeconomic inequalities in all-cause mortality [ 6 ]. While alcohol use itself was found to explain less than 30% of the socioeconomic inequalities in all-cause and alcohol-attributable mortality, there is some evidence of joint effects between alcohol use and low SES, contributing to the increased socioeconomic inequality in alcohol-attributable mortality [ 7 , 8 ].…”

Causal mechanisms proposed for the alcohol harm paradox—a systematic review

“…Otherwise, there was evidence to suggest that drinking patterns and clustering of health behaviours may play some role, as several cross-sectional studies highlighted that those of a low SEP tend to engage in heavier drinking patterns and multiple unhealthy behaviours [8,21,22,30,[39][40][41]. Those testing the causal role of risk behaviour (n = 13) found that these factors partially attenuate the AHP but could not fully explain excess harm experienced by lower SEP groups [3,4,9,18,[43][44][45][46][47][48]. For example, one record linkage study revealed that when adjusting for alcohol consumption, heavy drinking, BMI and smoking, the hazard ratio for the most deprived group compared to the least deprived was 2.71 [95% confidence interval (CI) = 2.01-3.64] [4].…”

Economic Recession and the Long Term Risk of Psychiatric Disorders and Alcohol Related Diseases—A Cohort Study From Eastern Finland

“…However, the alcohol harm paradox should be addressed cautiously, since low SEP groups are more vulnerable to higher alcohol-related harm even if they consume similar or lower levels of alcohol than higher SEP groups. Although the alcohol harm paradox is not yet fully understood, the joint effect of other adverse lifestyle factors such as smoking and obesity might partially explain the development of alcohol-related diseases among low SEP groups ( 34 ).…”