Discussion
The goal of the current study was to evaluate cognitive functioning in IDCs and identify (potential) risk factors as predictors for cognitive functioning in IDCs. This study showed that IDCs had worse executive functioning compared to control participants, a finding in line with the first hypothesis. Since caregiving often requires the capacity to make judgments, solve problems, recall necesarry information, and communicate effectively (7), all skills that invoke the executive functions (7,54), cognitive decline in IDCs, especially when affecting executive functioning, may affect the ability to provide adequate care (17). However, IDCs showed both better verbal immediate and delayed episodic memory in comparison to control participants.
Our findings regarding cognitive functioning in IDCs appear to be inconsistent, suggesting that the caregiver effect on cognitive functioning might vary per cognitive domain and is affected by several alternative mechanisms. First, all of the instruments used have been validated for the assessment of dementia, however contradictory caregiving effects on verbal memory might be a consequence of several shortcomings reported on the WMS-III: range restriction, problematic scoring floors, and confounding irrelevant factors are identified (55). Furthermore, Logical Memory had lower sensitivity and specificity for detecting dementia (respectively 48% and 92%) compared to both Letter Fluency (respectively 89% and 85%) and Category Fluency (respectively 100% and 92.5%) (56–58). Second, in general findings regarding worse cognitive performance in caregivers have not been consistent in the literature. A model labelled as the healthy caregiver hypothesis showed better health outcomes in some older caregivers compared to non-caregivers (59–63). This might be mediated by greater physical activity and more engagement in cognitive challenging tasks, such as making judgment or decisions, that could help to maintain physical and cognitive health in caregivers (33,59–63). Furthermore, IDCs might be more conscious about their memory since they have experienced memory changes in their proxy with dementia. Therefore they could worry about developing dementia themselves, but also practice and compensate more to maintain normal memory functioning. These variables might buffer the negative effects of caregiving stress on cognitive performance (59).
Nevertheless our findings support other research which indicated that caregivers perform worse on tasks involving attention and speed, but not on a word list memory test (10,17). Likewise, cognitive decline associated with stress and depression, which have a higher incidence in IDCs, mostly affects speed and subsequently both attention and executive function tasks with a speed component (20,21). IDCs also showed significant higher levels of both depression and anxiety in the current study. Furthermore, tasks that involve speed/executive functioning, in the current study the Fluency tasks, are especially sensitive to age but less sensitive in detecting MCI or dementia, since executive function is often impaired to a lesser extent in dementia as opposed to episodic memory which is related to preclinical Alzheimer’s Disease (64–66). In the current study the IDCs were significantly older than the control participants.
It is important to note that our results may underestimate the degree of cognitive decline experienced by the general population of IDCs. This may have occurred by excluding both individuals with physical disabilities and people with severe psychological problems, due to the inability to enter the simulator or the risk of getting confused by the dementia simulator, a relatively healthy, more physically active IDC group was included. Research suggests however that cognitive functioning might be positively related to physical function, especially to the ability to execute instrumental activities of daily living (15,67). Moreover, providing care for an adult might negatively affect physical health, particularly in case of psychologically distressed IDCs (11,12).
Concerning the second and third hypothesis, both unmodifiable and modifiable risk factors – which were either known from the literature or theory-driven but not yet explored – were investigated as predictors of cognitive functioning in IDCs. Regarding unmodifiable risk factors, this study found that age was the only significant predictor being responsible for most of the variance found in verbal memory storage and retrieval, with older people showing a worse cognitive performance. This result is consistent with the literature (25–27) and the current study where IDCs were significantly older compared to control subjects. In executive functioning, both being a spousal caregiver and spending more weekly hours on care of the care recipient explained a significant amount of variance in executive functioning and predicted worse executive functioning, on top of age. Spousal IDCs might be particularly vulnerable since this is strongly correlated with an older age (15,68). These results are supported by previous studies; an increase in hours of care has a negative effect on well-being, increases burden, and hereby indirectly affects cognitive functioning (69). It would be interesting for future research to look at how many hours spending on care has a negative effect on cognitive health.
With regard to the third hypothesis, none of the modifiable risk factors were significant predictors of verbal memory or retrieval in IDCs. This was surprising, since caregiver burden has been widely associated with impaired memory (17). This could be the result of a relatively healthy and highly educated population in this study with a bigger cognitive reserve leading to higher scores in verbal memory (70). In executive functioning, both less potential and actual social support, predicted a worse performance, which is supported by the literature (30,31,34,71,72). Results also showed significantly lower potential social support in IDCs compared to control subjects. Social support is positively associated with social networks and engagement and although exact mechanisms are still unknown, a commonly used explanation is that neural networks are preserved by participating in complex cognitive exchanges (31,71,73).
This study had some advantages: the sample size was relatively big, with more than 100 participants in each group. As a result, statistical assumptions were not violated and a sufficient powerlevel was reached. Second, three different neuropsychological tests measuring different cognitive domains were used as instruments for cognitive functioning.
Despite the advantages, results of this study must be interpreted in the context of its limitations. In contrast to the IDC participants, most participants included in the control group were recruited via private and professional networks. Moreover, the IDC group and the control group were recruited at different moments in time and both groups comprised a relatively low number of people with a low educational level, therefore generalizability of the current study might be limited. Second, study results can only be generalized to IDCs who are not physically disabled or known with severe psychological problems.
Another shortcoming is the use of unstandardized scores for the WMS since T-scores (corrected for the influence of age, gender, and educational level) were only available for Fluency tasks. In analyzing WMS scores only age was used as a covariate because independent samples t-tests showed baseline differences between groups for age, not for gender and educational level.
Fourth, the independent variable caregiver burden could only be measured in the IDC sample group and a variable regarding burden was not included in the control group. Therefore burden level could not be compared for both groups. Moreover, in the current study we did not control for possible relevant variables, such as the worksituation, and physical activity of the caregiver neither was a baselinelevel of cognitive functioning available.
Furthermore, the study included a relatively large number of both predictor and outcome measures. To minimize the possibility of type I errors, a stepwise approach to the statistical analysis was used. Besides, effect sizes of the results found were small and must therefore be interpreted with caution.
Finally, the cross-sectional design of this study precludes making causal inferences.
The findings of this study have some implications for clinical practice and further research. Results about the effects of caregiving on cognitive health found in previous studies are still contradictory. Nevertheless, clinical practice should not only pay attention to the person with dementia but also to the caregiver. Spousal older individuals, who spend a significant amount of hours on care or have low social support might be more vulnerable to adverse cognitive outcomes. Second, results demonstrate that the role of unmodifiable risk factors in predicting cognitive functioning in IDCs is bigger than the predictive value of modifiable risk factors. It would be interesting to look at cognitive performance over time with a prospective cohortstudy design, including more neuropsychological tests with better psychometric properties, and evaluate the role of unmodifiable and modifiable risk factors in establishing which IDCs have positive health outcomes and which will be negatively affected and develop dementia. Hereby our understanding of the caregiving effect on cognitive functioning can be increased so that it can be used by clinicians, researchers, and policy makers in order to improve care. Future studies would help to assess whether care needs to focus on modifiable risk factors possibly through implementing interventions which could help to maintain or bolster IDCs’ social network/support and protect IDCs’ capacity to care or on unmodifiable risk factors by increasing awareness about potential increased risk of dementia in IDCs so that policy makers can identify at-risk groups.
In short, our results show that IDCs have worse executive functioning compared to non-caregivers, but better verbal episodic memory. Age was the biggest predictor in cognitive functioning, but also being a spousal caregiver, spending more weekly hours on care, and feelings of poor social support tend to negatively affect executive functioning in IDCs. These findings suggest vulnerability of IDCs in cognitive decline and the role of risk factors. Periodic monitoring, in order to prevent harmful behavior towards the person with dementia and themselves, and evaluation of cognitive functioning over time of these vulnerable IDCs is strongly recommended.