Sleep and Cognition in Late-Life Depression

Depression commonly occurs with subjective as well as objective impairment in sleep and cognition.   However, few studies have examined the interaction between sleep impairment, cognition and depression in elderly cohorts.   Sleep disturbances predict increased risk for new onset depression and recurrence of depression in those with previous episodes.  Impaired sleep appears to reduce memory function and possibly reduce neurogenesis. 

Naismith and colleagues recently examined the correlations between sleep parameter and cognition in a group of 44 subjects with a lifetime history of depression (minimum age >45 years, mean 63 years) and a group of similarly aged adults without depression.  Neuropsychological testing in this study focused on domains felt to be impaired in mood disorders including: 1.) processing speed, 2.) attention, 3.)visual memory, 4.) verbal memory, 5.) language-as tested by counting number of animal names produced in one minute and 6.) executive function-planning, problem solving and response inhibition.

Sleep function was measured using actigraphy and sleep diaries.  Actigraphy typically involves using a wrist watch type device that measures movement during the night and provides an estimate of key sleep parameters including: 1.) total rest interval 2.) sleep latency—time from going to bed to falling asleep (in minutes), 3.) wake after sleep onset (WASO), 4.) arousals—number of periods during night where activity indicated being awake and 5.) sleep efficiency—the percent time asleep during the night

Elderly subjects with a history of depression (current depression ratings suggest a relatively mild depression cohort at time of study) showed increased WASO and decreased sleep efficiency (two highly correlated sleep variables).   WASO and sleep efficiency variables correlated with reduced cognitive function particularly in the domains of attention, memory (semantic and visual) and executive function.  Of note, late onset of depression tended to be associated with poorer sleep quality than earlier age of onset.  The authors controlled for depression severity in this study so the findings appear outside of this influence.

The authors suggest greater cognitive impairment in late onset depression may relate to white matter changes due to cerebrovascular disease.   White matter changes in frontal cortex-subcortical circuits have been associated with reduction in psychomotor speed and executive function.

The authors also note this study is unable to identify the sequencing and causal pathway for these relationships.  If impaired sleep directly impairs cognition, early identification of sleep abnormalities and treatment may limit associated cognitive impairment.  Sleep apnea also needs to be considered in this population, although the authors found no association between measures of sleep apnea and cognitive impairment.

The take home message from this study is that sleep impairment (poor efficiency) may be a marker for depression and cognitive impairment in those over 50.  Clinicians caring for the older adult, should carefully assess the health of the sleep of their patients and keep the sleep, cognition and depression triad in mind.  Sleep complaints in older adults need thorough assessment and should not be dismissed simply as age-related physiological in nature. 

Photo of Tiger Woods putting during practice for 2010 PGA championship courtesy of Yates Photography.

Naismith SL, Rogers NL, Lewis SJ, Terpening Z, Ip T, Diamond K, Norrie L, & Hickie IB (2011). Sleep disturbance relates to neuropsychological functioning in late-life depression. Journal of affective disorders PMID: 21435728