Social class differences in anxiety and depression across the life-course: evidence from three cohorts in the west of Scotland
Background
Studies of social inequalities in common mental disorders – anxiety and depression – often use measures that do not discriminate between conditions, but these disorders may differ from one another in their social patterning across the lifecourse. The Twenty-07 Study includes the Hospital Anxiety and Depression Scale (HADS), which has sub-scales for each condition, allowing possible differences in patterning to be examined.
Objective
To investigate the age trajectories for anxiety and depression by social class.
Design and Setting
Prospective cohort study of 4150 men and women, living in Clydeside, aged 15, 35 and 55 at baseline in 1987/8 and interviewed at five-year intervals for 20 years. HADS scores were obtained at each of four follow-up visits and growth curve modelling was used to assess the relationship between HADS caseness, age, sex and baseline social class across 10 629 measurement occasions from 3846 respondents. This sample is representative of those interviewed at baseline.
Results
There was a higher prevalence of anxiety than depression: 39.4% of the measurement occasions were defined as anxiety cases, 12.5% as depression cases, and 10.4% as cases for both disorders. There were significant non-linear age trajectories in caseness. The probability of anxiety caseness was relatively high in youth to middle-age and decreased with age thereafter. This age-related improvement was slower for those in manual, compared to non-manual, classes, and this class difference was larger for females. The probability of depression caseness was low in youth, and increased with age with a steeper increase for those in manual classes than for those in non-manual classes. The probability of having both anxiety and depression exhibited an inverse U-shaped trajectory, peaking in middle age, with a class difference in the age gradient similar to that for depression. Sensitivity analyses indicated that these findings were robust to period and cohort effects as well as sample attrition.
Conclusion
Anxiety and depression exhibit quite different trajectories across the lifecourse; the probability of anxiety reduces with age, whilst depression becomes more probable. There is a significant interaction between social class and age in both conditions, with those in manual classes having a slower reduction in anxiety and a faster increase in depression as they age than more affluent respondents. Future work should be sensitive therefore to how the social patterning of the two disorders differs across the lifecourse.
