There is a lot of literature investigating how lifestyle factors are associated with protecting cognitive decline in old age. The influence of lifestyle factors on cognitive ageing is of much interest as it is within an individual’s power to change their lifestyle given the knowledge of how it affects their cognition. By identifying what lifestyle factors are related to poorer cognitive function in older adults, individuals can take the necessary interventions to steer themselves on to the right path towards maintaining cognition throughout their lifespan and therefore ensure a better well-being and quality of life. Social factors include many aspects, such as social activities, social networks, social support, living situation and marital status (Hertzog et al., 2009). However this essay focuses on social isolation and loneliness. Depression is commonly included in studies with social isolation and loneliness and therefore is also considered. There is empirical evidence to suggest that both social isolation/loneliness and depression are related to level of cognition in old age, and this association will be discussed.
How social relationships are conceptualised is important as individuals may have a large social network and an active social lifestyle, but few close friends who they feel they can rely on. Considering there are many different ways of conceptualising social lifestyle, researchers need to ensure that their measurement does assess the factor it is supposed to. This is also true for measuring cognitive ability. Including specific domains instead of, or as well as, one general cognitive assessment is favoured in the literature as it allows researchers to examine whether the predictor variables have an influence on cognitive functioning as a whole, or if it only affects certain domains of cognition. DiNapoli et al. (2014) measured global cognition and four specific domains by assessing performance on 6 tasks. However, they warn readers to be cautious of the findings within the domains as some were based on one task and others were based on two, so there is a lack of consistency within the cognitive measurement.
This study investigated the effect of social isolation on cognitive function in older adults. The researchers suggest that social isolation is combined of two dimensions: social disconnectedness and perceived isolation and so these were included in the study as secondary predictors. The Lubben Social Network scale-6 (LSNS-6) was used to measure the three social predictors. Social disconnectedness was measured by 2 items from the scale; perceived isolation was measured using 4, and social isolation was the score of all 6. They were all found to have significant effects on global cognitive performance and on the four domains. Perceived isolation was found to affect cognition almost twice as much as social disconnectedness did. This suggests that while having more social relationships is important for maintaining cognition, how we personally feel about our relationships is more important. However, Cronbach’s alpha was considered when determining internal consistency of the LSNS-6 and social disconnectedness was not suggested to be a reliable measurement. This may be because Cronbach’s alpha is affected by the number of items included and social disconnectedness was only measured by 2 items. Because of this, the researchers warn readers to treat the association of social disconnectedness and cognition with caution, although it is unlikely that the result was hugely affected by this as it is consistent with previous findings.
This study is a good example of how social factors can be conceptualised in different ways. Social isolation is considered in this study as a combination of social disconnectedness and perceived isolation, whereas others consider social isolation and disconnectedness to be the same thing, and perceived isolation to be something separate. Cornwell & Waite (2009) refer to social isolation/disconnectedness as a lack of interaction with others, infrequent participation in social activities and a small social network. Loneliness, on the other hand, refers to perceived isolation and perceived disconnectedness from others, meaning it is about the dissatisfaction with social relationships, intimacy or support, rather than the physical absence of them. It could therefore be argued that there was not a need to measure social isolation as a combination of disconnectedness and perceived isolation, and instead these two factors should have been measured more extensively as separate entities.
Depression was included as a covariate. Although it significantly correlated with poorer cognitive performance it was not found to be significant in any of the main regression analyses and therefore was only briefly mentioned. The study included a very specific sample of Appalachian community-dwelling elders, presumably because of the “isolated” stereotype associated with Appalachia (Hsiung, 2015), although the study does not discuss this. The results therefore may not represent the overall elderly population. As well as ensuring adults were aged 70 or above and from West Virginia, they also had to have at least four natural teeth in order to participate but it is not explained why.
Wilson et al. (2007) focused on the effect of loneliness on cognition in old age. As it was a longitudinal study, some participants were lost but a total of 823 older adults were included in the final analysis. Cognitive ability was measured at baseline and at each follow-up. However, there was a discrepancy in the study as some participants were followed-up five times and others only twice, meaning that those who were assessed more may have performed better due to having more familiarity with the tests.
Loneliness was measured using a modified version of the de Jong-Gierveld Loneliness scale. The original scale was made up of two components: emotional loneliness and social loneliness. Emotional loneliness is considered the lack of a close intimate relationship such as a partner or a best friend and social loneliness is considered as the lack of a social network or group of friends (De Jong Gierveld & Tillburg, 2006). However this study only measured emotional loneliness. Two other minor changes were made but it was still found to be a valid and reliable measurement. Social isolation was also measured using standard questions assessing network size and frequency of social activity. Loneliness was related to cognitive ability at baseline on each cognitive measure, and also to more decline over time in global cognition and in three of the five domains. The longitudinal design allowed researchers to not only observe the effect of loneliness at one point in time but also examine the interaction between loneliness and time and how they affect cognition together.
Participants were all free of dementia at the beginning of the study but over the four years 76 participants developed signs of dementia that met the criteria for Alzheimer Disease (AD). It was found that lonely individuals were 2.1 times more likely to develop AD than those who were not lonely. Social network was not related to incidence of AD but perceived loneliness was which suggests that the quality of relationships is more important than the quantity for developing AD. Depressive symptoms were also assessed with a 10-item version of the Centre for Epidemiological Studies – Depression (CES-D) scale. 1 item asked about loneliness and was analysed separately from the remaining 9. This 1 question about loneliness showed a stronger relationship with development of AD than depression did when it was measured using the remaining 9 items. This suggests that loneliness affects cognition more than depression does. When loneliness was analysed with the risk of developing AD, but depression was controlled for, there was a modest reduction in the association showing that loneliness is partly determined by depressive symptoms. However, when depression and AD were analysed controlling for loneliness, there was a much larger reduction of association, suggesting that loneliness may be an important aspect of the relation between AD and depression.
The researchers explored the possibility of reverse causation, which means that loneliness is a consequence of cognition decline instead of it being a cause or contributing factor. They were able to do this as they carried out a post-mortem examination of the brain in the participants who passed away in order to quantify AD pathology and cerebral infarctions. These were not found to have an association with loneliness and therefore do not support the possibility of reverse causation. However this is a very complicated subject and more research is needed. The more likely explanation suggested is that loneliness has a negative effect on the neural systems underlying cognition which is why lonelier individuals experienced more cognitive decline.
Luanaigh et al. (2011) also investigated the effect of loneliness, specifically on different domains, in elders free of dementia. A doctor and a researcher visited the participants’ homes to assess them. This could be viewed as a strength of the study as it meant participants would feel more comfortable in their own homes, especially since they have willingly agreed to this, compared to having to travel to an unfamiliar environment, which could also cause fatigue. The Mini Mental State Examination was included as a way of measuring global cognition which is a very brief cognitive test. A detailed psychometric test, much like those used to measure the several domains, would have been better. The measurement of loneliness contained only one question: “do you feel lonely?” Although there were four possible answers to this question, it could be argued that one item is not enough for adequate measurement. On the other hand, it could also be argued that asking the direct question if an individual feels lonely is an accurate and sufficient measure of loneliness. Those who answered ‘sometimes’ and ‘often’ were grouped together in the ‘lonely’ group, and those who answered ‘rarely’ and ‘never’ were grouped in the ‘not lonely’ group. This meant that the severity of loneliness was not considered. Overall, loneliness was found to be significantly associated with global cognition even when depression and social networks were controlled for. The two domains most strongly associated with loneliness were processing speed, which is consistent within the research, and delayed visual memory, which is a new finding and therefore requires more research.
Just like the problems of conceptualising social isolation, there are also problems with conceptualising depression. There are many severities of depression, which Dillon et al. (2014) explores. 118 depressed older adults and 40 healthy controls were matched on age and education. One problem with this is that for every 12 depressed participants there are only 5 controls. There were four subtypes of depression: Major Depression Disorder; Dysthymia Disorder; Subsyndromal Depression Disorder; and Depression due to (mild Alzheimer) dementia. Those who had moderate-severe dementia were excluded from the study.
Global cognitive performance was worse for the depressed group than the controls suggesting that depression is associated with poorer cognitive functioning in old age. All four sub-types showed impairments with memory, however this could be due to the fact that they were recruited from a memory clinic, meaning it is a biased sample as they all had memory complaints. Aside from memory, the subtypes all showed impairments with different domains. This illustrates the importance of measuring both global cognitive function and specific domains, and also of looking at different subtypes of depression instead of only depressive symptoms.
Overall, the research shows that depression and social isolation/loneliness in old age are related to poorer cognitive functioning. It is suggested that how individuals perceive their social relationships is more important than number of relationships when it comes to cognition. Therefore interventions should focus on perceived support and loneliness. As the studies are of observational design, the direction of the relationship is unclear. It is not possible to say that depression or loneliness cause cognitive decline as they could in fact be consequences of the decline. The relationship between depression and loneliness is also complicated as one could influence the other. As mentioned in one study, a depression scale asked about loneliness and therefore researchers need to ensure their measurements are valid. Longitudinal studies are able to look at level of decline over time but cross-sectional studies are not, and therefore more longitudinal research would be useful to understand how the period and severity of depression and loneliness affect how cognition changes with time.
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