Background Living in social disadvantage has been conceptualised as a chronic stressor, although this contradicts evidence from recent studies using hair cortisol as a measure of hypothalamus-pituitary-adrenal (HPA) axis activity. The methodological limitations of previous studies investigating the association between socioeconomic position (SEP) and hair cortisol and cortisone are taken into account in this study which examines if lower SEP is associated with higher levels of HPA axis activity as measured by hair cortisol and cortisone among older adults.
Methods Cortisol and cortisone levels in hair samples from 2468 participants in the 6th wave of the English Longitudinal Study of Ageing (ELSA) are examined, in relation to educational attainment, wealth, social class, and employment status. Multivariable linear regression models were used to examine the association between socioeconomic position and cortisol and cortisone levels. Inverse probability weighting and multiple imputation were used to compensate for missing data. Interactions between social class and employment status were tested. All models were adjusted for gender, age, interaction between gender and age, ethnicity, marital status, hair treatment, hair colour, nurse visiting month, smoking status, body mass index, self-assessed health, number of medications, and depressive symptoms.
Results We found significant differences between the most and least advantaged social classes in their levels of hair cortisol and cortisone. Participants in the lower supervisory social class and retired had increased levels of cortisol (0.71 log(pg/mg), 95% CI 0.14 to 1.28) and cortisone (0.73 log(pg/mg), 95% CI 0.29 to 1.16) compared to participants in the most advantaged social class and those still in work. Among the economically inactive, the most disadvantaged social classes clearly had increased levels of hair cortisol and cortisone. Further analyses that take missing data into account showed that the complete case estimates of hair cortisone in the most disadvantaged groups were underestimated compared to estimates accounting for missing data, such as inverse probability weighting and multiple imputation.
Conclusion This study demonstrates that social disadvantage as measured by low SEP is correlated with increased HPA axis activity. The conceptualisation of social disadvantage as a chronic stressor may be valid and previous studies reporting no associations between SEP and hair cortisol may have some methodological limitations. Future analyses using biosocial data may need to take into account and adjust for missing data in biosocial analyses.
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