Age Moderates the Link between Epilepsy and Self-Rated Health (SRH)

Epilepsy is one of the most severe neurological diseases that affect people around the globe. Self-rated health (SRH) refers to one’s subjective evaluation of their own health and is associated with various outcomes such as morbidity and mortality. Thus, understanding the association between epilepsy and SRH is of great importance. Moreover, SRH generally decreases with age. The aim of the current study is to test whether age moderates the link between epilepsy and SRH. The current study used a hierarchical regression and three multiple regressions to analyze the associations between epilepsy and SRH in 529 epilepsy patients and 46,978 healthy controls from the United Kingdom. The current study found that age significantly moderates the association between epilepsy and SRH. Specifically, epilepsy status was negatively related to SRH in young people (b = −0.69, p < 0.001, 95% C.I. [−0.84, −0.54]), more strongly in middle-aged adults (b = −0.81, p < 0.001, 95% C.I. [−0.95, −0.66]), and most strongly in older adults (b = −0.89, p < 0.001, 95% C.I. [−1.09, −0.69]). The current study may imply that older adults need more attention in terms of their SRH, which is closely associated with outcomes. Clinicians and health professionals should come up with ways that improve SRH in people with epilepsy, especially for older adults with epilepsy.


Introduction
To better identify and track the burden of epilepsy in communities, it is important to develop and enhance the infrastructure and capacity for surveillance and epidemiologic studies of people with epilepsy and is as a key priority in doing so [1]. Burdens induced by epilepsy include both social and personal dimensions, which could cause direct and indirect costs such as health care costs, impaired well-being, and can negatively affect physical and mental health (see [2]).
Self-rated health (SRH) refers to one's subjective evaluation of their own health and has been widely used as an indicator of general health in healthy research at the population level, which integrates biological, functional, mental, and social aspects of a person [3]. Although SRH is non-specific, it has good predictive validity, as demonstrated by its associations with various health-related conditions such as stroke, lung disease, arthritis, functional impairment, cardiovascular disease, depression [4], and outcomes such as morbidity and mortality [5]. There are few studies that have looked at SRH in epilepsy patients. For instance, Kobau et al. [2] found that adults with active epilepsy and with a history of epilepsy were more likely to report fair or poor health in a cohort from the United States. Kang (2022) found that epilepsy patients are characterized by poorer SRH compared to healthy controls [6].
Age is also a consistent predictor of SRH, given that objective health decreases with age. Indeed, studies have found that SRH declines with age (e.g., [7,8]). These declines could be also explained by age-related health conditions. For instance, cardiovascular disease is more prevalent in older people compared to younger people [9]. Several studies suggested that health conditions are the most critical factors for formulating the subjective health evaluation change across age, independent of gender [10].
Thus, one would suspect that age moderates the link between epilepsy and SRH, and understanding how epilepsy is associated with SRH has a profound meaning in terms of understanding the outcomes, as SRH is predictive of various health-related outcomes.
The aim of the current study is to investigate how age moderates the associations between epilepsy and SRH.

Data
This study extracted data from Understanding Society: the UK Household Longitudinal Study (UKHLS), which has been collecting annual information from the original sample of UK households since 1991 (when it was previously known as The British Household Panel Study (BHPS). This dataset is publicly available at https://www.understandingsociety. ac.uk/documentation/mainstage, accessed on 10 September 2022. All data collections have been approved by the University of Essex Ethical Committees. Participants received informed consent before participating in these studies. Data were used from Wave 1, which was collected between 2009 and 2010 [11]. There were 529 epilepsy patients and 46,978 healthy controls in the current study. Descriptive statistics can be found in Table 1. Self-reported epilepsy is a valid measure to identify epilepsy at a population level (e.g., [12]). Participants answered the question "Has a doctor or other health professional ever told you that you have any of these conditions? Epilepsy." to indicate if they have epilepsy.

SRH
Participants responded to the question, "In general, would you say your health is..." using a 5-point scale ranging from 1 (excellent) to 5 (very poor). The reliability of this single measurement of subjective health is moderate (e.g., [13]). SRH was reverse coded, so now 1 = very poor and 5 = excellent.

Demographics Variable
Demographic variables include age, sex (male vs. female), monthly income, highest educational qualification (college vs. under college), and marital status (married vs. not currently married).

Analysis
A hierarchical regression model [14] with demographic variables including age, sex, monthly income, highest educational qualification, marital status, epilepsy status, and epilepsy status by age interaction was taken into the model as predictors to predict SRH. Participants were then grouped into three groups based on their age, including young (16 and 35), middle-aged (35 to 55), and older people (above 55). Finally, three multiple regressions were used by taking demographic variables including age, sex, monthly income, highest educational qualification, and marital status; these variables were taken into the model as predictors of SRH for young, middle-aged, and older people.

Results
Descriptive statistics can be found in Table 1. The current study found that age significantly moderates the association between epilepsy and SRH (b = −0.009, p < 0.  Table 2 and visualized in Figure 1. Table 2. The regression coefficient (b) for the demographics and epilepsy status with the total explained variances (R 2 ) for young, middle-aged, and older people. All numbers were rounded up to two digits. *** p < 0.001.

Young
Middle

Discussion
The aim of the current study was to investigate whether age moderates the link between epilepsy and SRH. By using a hierarchical regression and three multiple regressions on data from 529 epilepsy patients and 46,978 healthy controls, the current study found that age significantly moderates the association between epilepsy and SRH. Specifically, epilepsy status was negatively related to SRH in young people, more strongly in middle-aged adults, and most strongly in older adults.
The findings that epilepsy status is negatively associated with SRH across age groups seem to be consistent with previous studies (e.g., [2,6]). Indeed, epilepsy patients face a lot of challenges in their daily life including poor health, reduced physical activities, higher inflammation rate, more disability, and more risky behaviors [15][16][17][18]. Second, perceived limitations in social and emotional support can also lead to poor SRH, given that SRH is not only a reflection of objective health but also incorporates psychosocial aspects of a person. Third, neurological factors have adverse impacts on the SRH in people with epilepsy [19] as well. These challenges may in turn explain the poorer SRH in the current study.
The main finding of the current study was that age significantly moderates the association between epilepsy and SRH. Indeed, previous studies have found that SRH declines with age (e.g., [7,8]). Young people with a diagnosis of epilepsy had poorer SRH compared to healthy controls. However, this effect was larger in older participants. Older adults with declined health may be more sensitive to their diagnosis of epilepsy and may be more impeded by their epilepsy, which may then result in poorer SRH. Older adults with a diagnosis of epilepsy may also have awareness of their impaired physical health, which strengthens the link between epilepsy and SRH.
Despite the strengths of the current study, including a large data set and well-controlled sociodemographic characteristics, there are some limitations of the current study. First, the current study relied on self-reported data, which cannot avoid self-reporting bias. Future studies should confirm epilepsy status with medical diagnosis. Second, the current study is cross-sectional, which cannot establish causality. Future studies should use longitudinal approaches to establish casualties if possible. Third, the current study focused on participants from the United Kingdom, which may make it hard to generalize the current findings to other countries and cultures. Future studies should test how age may moderate the associations between epilepsy and SRH in various countries and cultures. Finally, unmeasured variables may contribute to the results of the current study, such as the frequency of seizures, discrimination, and stigmas. Future studies should control for these confounding variables.

Conclusions
Taken together, the current study found that age moderates the link between epilepsy and SRH, with older adults having the strongest negative association between epilepsy and SRH. The current study may imply that older adults need more attention in terms of their SRH, which is closely associated with outcomes. Clinicians and health professionals should come up with ways that improve SRH in people with epilepsy, especially for older adults with epilepsy. Specifically, social participation should be encouraged, as participation in the community salon was associated with improvements in SRH over time [20]. Moreover, eHealth tools can also be useful for encouraging healthy behaviors and improving SRH [21]. Moreover, as demonstrated by the results from the current study, obtaining at least a college degree and being married are also associated with better SRH. Moreover, one study has found that being involved in vigorous or moderate physical activities and frequently consuming legumes and eggs is associated with better SRH [22].
Funding: This work was supported by the Imperial Open Access Fund.
Institutional Review Board Statement: Ethics approval was received from the University of Essex Ethics Committee.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement:
Publicly available datasets were analyzed in this study. This data can be found here: https://www.understandingsociety.ac.uk (accessed on 21 September 2022).

Conflicts of Interest:
The author declares no conflict of interest.