Associations between depression symptom burden and delirium risk: a prospective cohort study

BACKGROUND AND OBJECTIVES: Delirium and depression are increasingly common in aging. There is considerable clinical overlap, including shared symptoms and comorbid conditions, including Alzheimer’s disease (AD), functional decline, and mortality. Despite this, the long-term relationship between depression and delirium remains unclear. This study assessed the associations of depression symptom burden and its trajectory with delirium risk in a 12-year prospective study of older individuals during hospitalization. RESEARCH DESIGN AND METHODS: 319,141 UK biobank participants between 2006–2010 (mean 58y [range 37–74, SD=8], 54% female) reported frequency (0–3) of four depressive symptoms (mood, disinterest, tenseness, or lethargy) in the preceding 2 weeks, and aggregated into a depressive symptom burden score (0–12). New-onset delirium was obtained from hospitalization records during 12y median follow-up. 40,451 (mean age 57±8; range 40–74y) had repeat assessment on average 8y after their first. Cox proportional hazard models examined whether depression symptom burden and trajectory predicted incident delirium during hospitalization. RESULTS: 5,753 (15 per 1000) newly developed delirium during follow-up. Increased risk for delirium was seen for mild (aggregated scores 1–2, hazards ratio, HR=1.16, [95% confidence interval 1.08–1.25], p<0.001), modest (scores 3–5, 1.30 [1.19–1.43], p<0.001) and severe (scores ≥ 5, 1.38 [1.24–1.55], p<0.001) depressive symptoms, versus none in the fully adjusted model. These findings were independent of the number of hospitalizations and consistent across hospitalization settings (e.g., surgical, medical, or critical care) and specialty (e.g., neuropsychiatric, cardiorespiratory or other). Worsening depression symptoms (≥1 point increase), compared to no change/improved score, were associated with an additional 39% increased risk (1.39 [1.03–1.88], p=0.03) independent of baseline depression burden. The association was strongest in those over 65y at baseline (p for interaction <0.001). DISCUSSION AND IMPLICATIONS: Depression symptom burden and worsening trajectory predicted delirium risk during hospitalization. Increased awareness of subclinical depression symptoms may be warranted for delirium prevention.