Abstract
Evidence on systemic inflammation as a risk factor for future depression is inconsistent, possibly due to a lack of regard for persistency of exposure. We examined whether being inflamed on multiple occasions increases risk of new depressive symptoms using prospective data from a population-based sample of adults aged 50 years or older (the English Longitudinal Study of Ageing). Participants with less than four of eight depressive symptoms in 2004/05 and 2008/09 based on the Eight-item Centre for Epidemiologic Studies Depression scale were analysed. The number of occasions with C-reactive protein ⩾3 mg l−1 over the same initial assessments (1 vs 0 occasion, and 2 vs 0 occasions) was examined in relation to change in depressive symptoms between 2008/09 and 2012/13 and odds of developing depressive symptomology (having more than or equal to four of eight symptoms) in 2012/13. In multivariable-adjusted regression models (n=2068), participants who were inflamed on 1 vs 0 occasion showed no increase in depressive symptoms nor raised odds of developing depressive symptomology; those inflamed on 2 vs 0 occasions showed a 0.10 (95% confidence intervals (CIs)=−0.07, 0.28) symptom increase and 1.60 (95% CI=1.00, 2.55) times higher odds. In further analyses, 2 vs 0 occasions of inflammation were associated with increased odds of developing depressive symptoms among women (odds ratio (OR)=2.75, 95% CI=1.53, 4.95), but not among men (OR=0.70, 95% CI=0.29, 1.68); P-for-sex interaction=0.035. In this cohort study of older adults, repeated but not transient exposure to systemic inflammation was associated with increased risk of future depressive symptoms among women; this subgroup finding requires confirmation of validity.
Highlights
Mental disorders contribute greatly to the global burden of disease[1] and depression is the largest driver of morbidity associated with these disorders.[2]
We examined whether repeated exposure to systemic inflammation increases the risk of developing new depressive symptoms by analysing repeated measures of C-reactive protein (CRP) from a population-based sample of older adults
A total of 2068 participants were free of depressive symptoms in 2004/05 and 2008/09 and had data on CRP on those same occasions, had follow-up data on depression status in 2012/13, and had data on covariates in 2008/09
Summary
Mental disorders contribute greatly to the global burden of disease[1] and depression is the largest driver of morbidity associated with these disorders.[2]. It is reasonable to expect that pro-inflammatory signals need to persist over time in order to induce depression; most studies conducted far have measured inflammation only once and cannot capture these potential effects. This leaves unanswered the question of whether exposure to systemic inflammation is associated with risk of developing depression in a dose–response manner; an observation that would support an argument for causality
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