Implications for practice and research

• Population ageing is expected to produce a dramatic increase in the number of individuals with dementia.

• Patients’ social isolation and loneliness are potentially modifiable risk factors for poor cognitive functioning.

• Attention to a patient's social environment may help preserve cognitive functioning in at-risk older adults.

Context

With the dramatic increase in life expectancy in developed countries, it has become important to identify factors that may mitigate the rising prevalence of cognitive dementia. The social environment in which older adults live has been linked to dementia, but the specific features of the social environment that are predictive have been elusive. Shankar and colleagues investigated the extent to which social isolation and perceived social isolation (loneliness) were predictive of declines in cognitive functioning.

Findings

At baseline, 13.1% of the participants reported depression, 1.7% loneliness and 4.8% isolation. Loneliness and isolation were both positively associated with a series of covariates, such as depression, CVD, smoking and diagnosed diabetes. Higher scores of loneliness and isolation were also associated with poorer cognitive function. After 4 years, the mean scores of cognition were significantly lower than at baseline, although the mean differences were small. After adjusting for covariates, loneliness and isolation were associated with poor memory among those low in education, and isolation was associated with poorer cognitive performance at follow-up.

Commentary

Loneliness has previously been related to various aspects of cognition, including cognitive decline and the onset of dementia in the elderly.1 There are several differences between prior studies and the present study, however, so it is useful to explain this discrepancy.

First, both experimental and longitudinal research indicates that loneliness increases depressive symptomatology.1 Consistent with this research, Shankar and colleagues reported that loneliness (but not isolation) was moderately correlated with their measure of depression. If loneliness were to alter cognitive functioning through its effects on depression or through a different but correlated mechanism, the inclusion of depression as a covariate in the initial analyses may mask the true association between loneliness and cognition.

Second, prior population-based studies of cognitive decline and dementia in older adults, including the Health and Retirement Study,2 the Cardiovascular Health Study,3 the Framingham Study4 and the Sacramento Area Latino Study on Aging,5 specified the minimum requirements for the diagnosis of dementia as a cognitive impairment in at least two domains reflecting a decline from prior levels, and sufficient severity to affect daily functions. By contrast, Shankar and colleagues did not aggregate results across cognitive tasks or measure the effects on daily functions, but instead separately analysed the scores of participants on each of the three specific cognitive tasks.

Third, most prior studies investigated changes in cognition over periods of time at least twice as long as examined by Shankar and colleagues. The extent to which the small mean changes in performance over 4 years reflect age-related cognitive declines or dementia is uncertain. The authors raise important questions about the relevance, importance and practical implications of social isolation and loneliness on cognitive function in older adults, but the answers to these questions must await future research.