Commentary

Recent longitudinal research suggests that social and emotional isolation in old age increase the risk of cognitive decline and dementia.1 The study by Crooks and colleagues showing an association between one’s social network and subsequent risk of developing dementia is a good example of this work. Importantly, social network was measured with two questions about its size (ie, number of friends, relatives seen or heard from at least monthly) and four questions about perceived supportiveness and trustworthiness of others. Studies that have defined social networks solely by their size have had inconsistent results whereas studies, such as the present one, that have included data about perceived quality of relationships have generally found an association with dementia. Thus it is not simply the number of people with whom we maintain regular contact but also (and perhaps more so) the quality of the underlying relationships that is critical.

A novel feature of this study is that almost all data collection was done by telephone, including cognitive testing and structured informant interview in the event of cognitive impairment. The results provide further evidence that clinical assessment by telephone is a valid and cost effective alternative to in person assessment.

The basis of the association between social network size and dementia is uncertain. A recent clinical–pathological study found that network size was not related to measures of Alzheimer’s disease pathology but modified the relation of pathology, especially neurofibrillary tangles, to cognition.2 Thus the processes involved in developing and maintaining a large social network may somehow help the brain to better tolerate the accumulation of age related neurodegenerative changes. Understanding the neurobiological mechanisms linking factors such as social network size to risk of dementia may suggest novel strategies for delaying age related loss of cognition function.