Despite the high prevalence of late-life depression
at threshold and subthreshold levels, their joint role in the disablement process remains unclear. This study aims to examine the association of comorbid occurring depression
across the full spectrum of symptom severity with disability
onset in older adults.
The study included 3663 participants from the 2011 National Health and Aging
Trends Study, who reported no limitations in self-care and mobility activities at baseline. Disability
onset was defined as a report of receiving help from another person in any of the activities for 3 consecutive months. Depression
symptoms were measured using the four-item Patient Health Questionnaire, grouped into low, mild, and moderate/severe symptom groups. Cox proportional hazards models were used to estimate relative risks for disability
onset over a 5-year period by depression
A total of 1047 participants developed disability
(24.6%; 6.0 per 1000 person-months). At baseline, one-fifth of the sample reported symptoms that were mild (n
= 579 [14.9%]; 31.6% with disability
onset) or moderate/severe (n
= 156 [4.2%]; 38.1% with disability
onset). After adjustment for sociodemographics, there was a dose-response relationship between depression
symptom groups and disability
onset (mild versus low: hazard ratio [HR] = 1.43, 95% confidence interval [CI] = 1.20–1.70; moderate/severe versus low: HR = 1.94, 95% CI = 1.45–2.59). The increased risk remained significant after adjustment for health status variables for the mild symptom group (HR = 1.26, 95% CI = 1.07–1.49), but not for the moderate/severe symptom group (HR = 1.30, 95% CI = 0.94–1.79), possibly reflecting lower statistical power.
Findings suggest that the full spectrum of depression
symptoms are associated with increased risk for disability
in late life. Their role in the disablement process warrants further investigation.