Socioeconomic status as an effect modifier of alcohol consumption and harm: analysis of linked cohort data
Research in context
Evidence before this study
The researchers initially searched MEDLINE and Embase in March, 2013, using keywords including “alcohol”, “socioeconomic status”, “socioeconomic position”, “deprivation”, and “inequalities”. Previous studies suggested a potential increased risk of harm for similar alcohol consumption levels among socioeconomically disadvantaged populations, but whether this hypothesis is correct remains unclear. A systematic review published in 2015 on the relation between socioeconomic status, alcohol consumption, and alcohol-attributable harms concluded that studies investigating the interaction between alcohol-attributable disease, socioeconomic status, and alcohol use are scarce.
Added value of this study
The researchers’ study is the largest to date investigating whether socioeconomic status effect modifies the relation between alcohol consumption and harm, and is the only one to investigate a range of potential alternative explanations, including reverse causation. Using high-quality survey data linked to admissions, mortality, and community prescriptions, we eliminated several important biases as potential explanations for the higher burden of alcohol-attributable harms in more socioeconomically disadvantaged populations. Alcohol consumption and binge alcohol use did not differ substantially with socioeconomic status. Despite this finding, the risk of harm was increased strikingly among socioeconomically disadvantaged populations.
Implications of all the available evidence
Alcohol-attributable harms are a major contributor to health inequalities. The body of available evidence indicates that this differential burden does not arise simply as a result of higher risk consumption among socioeconomically disadvantaged groups.
Efforts to target alcohol consumption by socioeconomic status are unlikely to be successful in reducing health inequalities, unless alcohol consumption cultures in the most disadvantaged populations differ systematically from societal norms. Interventions seeking to reduce consumption across the whole population are more likely to result in greater reductions in absolute health inequalities than previously thought.
Further research is needed to investigate the reasons for the noted effect modification.
Alcohol-related mortality and morbidity are high in socioeconomically disadvantaged populations compared with individuals from advantaged areas. It is unclear if this increased harm reflects differences in alcohol consumption between these socioeconomic groups, reverse causation (ie, downward social selection for high-risk alcohol users), or a greater risk of harm in individuals of low socioeconomic status compared with those of higher status after similar consumption.
The researchers aimed to investigate whether the harmful effects of alcohol differ by socioeconomic status, accounting for alcohol consumption and other health-related factors.
The Scottish Health Surveys are record-linked cross-sectional surveys representative of the adult population of Scotland. The researchers obtained baseline demographics and data for alcohol consumption (units per week and binge alcohol intake) from Scottish Health Surveys done in 1995, 1998, 2003, 2008, 2009, 2010, 2011, and 2012. The researchers matched these data to records for deaths, admissions, and prescriptions.
The primary outcome was alcohol-attributable admission or death. The relation between alcohol-attributable harm and socioeconomic status was investigated for four measures:
- education level,
- social class,
- household income, and
- area-based deprivation
To investigate the relation between alcohol-attributable harm and socioeconomic status the researchers used Cox proportional hazards models. The potential for alcohol consumption and other risk factors (including smoking and body-mass index [BMI]) mediating social patterning was explored in separate regression models. Reverse causation was tested by comparing change in area deprivation over time.
50 236 participants (21 777 men and 28 459 women) were included in the analytical sample, with 429 986 person-years of follow-up. Low socioeconomic status was associated consistently with strikingly raised alcohol-attributable harms, including after adjustment for weekly consumption, binge alcohol use, BMI, and smoking.
Evidence was noted of effect modification; for example, relative to light alcohol users living in advantaged areas, the risk of alcohol-attributable admission or death for excessive alcohol users was increased (hazard ratio 6·12, 95% CI 4·45–8·41 in advantaged areas; and 10·22, 7·73–13·53 in deprived areas).
The researchers found little support for reverse causation.
Disadvantaged social groups have greater alcohol-attributable harms compared with individuals from advantaged areas for given levels of alcohol consumption, even after accounting for different alcohol use patterns, obesity, and smoking status at the individual level.