We assessed demographic characteristics, lifestyle factors and health indicators that might associated with overall frailty as well as three domains of frailty within a diverse population group from five European countries. The present study confirms previous findings on association between factors (e.g. female sex, education level, country, physical activity, multi-morbidity, medication risk, and malnutrition) and frailty and its three domains. Remarkably, it shows that age was not associated with psychological and social frailty; sex was not associated with social frailty; people at risk of alcohol use had a lower risk of overall frailty and physical frailty; and smoking was not associated with frailty nor its three domains.
Demographic characteristics
The present study confirms [
41,
42] that overall frailty, and especially physical frailty, is highly associated with age. Remarkably, age was not associated with psychological or social frailty. Although age itself could be a risk factor for one’s physical condition due to human physiology, age may not necessarily be a specific risk factor for psychological and social frailty. For example, an older person might lose his or her spouse, then start to live alone and becomes isolated, which is an adverse life event that may negatively influence the psychological dimension of frailty. Moreover, if people cannot participate in social groups to the same extent as they had previously due to reasons independent of age, social resources that are essential for fulfilling their basic social needs may be lost. Consequently, this loss may lead to social frailty. These situations can happen at any stage of a person’s life, and are not by definition associated with older age. In this perspective, it is a specific adverse life event, rather than age, that may affect the psychological and social dimension of frailty. The age range of the participant is 70 to 102 y (the mean age is 79.7 ± 5.7), which is not a very diverse age population. A previous study illustrated that psychological frailty was affected by life events among community-dwelling persons aged 75 years and older [
43]. People within this age range already experienced several life events. Their ability to cope with different situations, even the ability to recover from an adverse event, may be higher than in younger age. This may explain why age in itself was not to be a risk factor predictive of becoming psychologically or socially frail in our study.
Our results confirm previous findings [
1,
44] that women, compared to men, have a relatively higher risk of having overall, physical and psychological frailty. Previous studies [
41,
45] have suggested that older men have a greater likelihood of dying suddenly, while women more often show a steady decline, associated with an increase in co-morbidity and disability. Therefore, women might be frail more often, compared to men. Remarkably, in our study, sex was not associated with social frailty; this contradicts earlier findings [
46,
47]. This non-consensus might be due to the different concepts of social frailty. In our study, three items were considered: living alone, missing having people around and receiving enough support from other people. However, social frailty is a relatively unexplored concept. To study the association between sex and social frailty, a more precise concept of social frailty and the developing pathways need to be explored in depth.
We found some differences regarding overall frailty and its three domains in the populations off Greece, Croatia and Spain, compared to the Netherlands. These differences could be explained by differences in socioeconomic, political and cultural backgrounds [
48]. Advanced levels of democracy and egalitarian political traditions may contribute to the population health improvement of a country’s population and to a lower prevalence of frailty [
49]. Further studies should be conducted to explore these differences between countries and to provide explanations for them.
In our study, migration background was not associated with overall frailty, nor with physical, psychological or social frailty. However, our study has a relatively low number of participants with a migrant background (n = 194), which might have reduced the power to detect such associations. To investigate the associations more comprehensively, we, therefore, recommend future studies with a larger number of participants from a migration background.
Our results show that people who completed secondary or an equivalent education have a relatively higher risk of overall, physical and psychological frailty. Education level was associated with frailty components, such as (instrumental) activities of daily living ((I)ADL), and self-rated health in several studies [
48,
50]. Previous studies have concluded that people with a lower education level are, on average, frailer than people with a higher education level [
51]. However, in our study, a tertiary or higher education level was not statistically significantly associated with overall frailty and its domains. It might be that the power of our study was too low to explore the association between educational level and frailty (211participants with tertiary or higher education).
We found that people who lived alone had a higher risk of overall frailty and social frailty, but a lower risk of physical frailty. People living alone had a lower risk of physical frailty might be because they were more likely to manage all the housework and other daily living tasks by themselves, thereby offering more opportunities to engage in physical activities. In line with this result, physical activities could contribute to reducing the risk among older people of being overall frailty as well as physical, psychological and social frailty. We found that the association between living alone and psychological frailty was not statistically significant. This finding can be explained by the fact that older people living alone may not be able to recognize mental health problems due to their social and financial vulnerability and the lack of proper formal/informal personal support. In light of this, it is possible that psychological frailty might also remain unrecognized. More studies are needed to clarify these findings.
With regard to social frailty, it should be noted that ‘living alone’ is one of the three items that defines social frailty in the Tilburg Frailty Indicator [
26]. Because of this definition, the association between ‘household composition (i.e. living alone)’ and social frailty is artificially increased; therefore, we performed additional analyses with a definition of social frailty based on two items (excluding the item ‘living alone’). To define the dichotomous variable ‘social frailty-2 items’, we applied a cut-off score of 2 points as well as 1 point. With a cut-off of 2 points, Household composition-living alone was significantly associated with social frailty in the multivariable model (OR = 1.53,
P < 0.01); with a cut-off of 1 point, this association was also significant (OR = 2.15,
P < 0.001). So, ‘living alone’ is independently associated with social frailty. For example, after the loss of a partner and then living alone, the subsequent potential loss of social resources and activities may induce social frailty. Additionally, we made a multivariable model of the potential factors except ‘household composition-living alone’ and ‘social frailty-3 items’ (the original definition). This model showed that also age and sex were significantly associated with social frailty (
p < 0.05). See Supplementary Table
S2.
The impact of ‘living alone’ on social frailty might differ between women and men [
11,
52] because of different ways of dealing with social situations. In both the original analyses and the additional analyses with a 2-item definition of social frailty, among men the association between living alone and social frailty was stronger than among women (see Supplementary Table
S3). Further research is therefore needed to explore the differences between men and women regarding the impact of household composition on social frailty.
Lifestyle factors
Remarkably, the results showed that people ‘at risk of alcohol use’ had a relatively lower risk of overall frailty and physical frailty; moreover, there was no association with psychological and social frailty. These findings was in contrast with a previous research [
53]. An explanation for this might be that alcohol may often be consumed in a moderate and socially accepted way; accordingly, moderate consumption may facilitate social bonding [
54]. It has been illustrated that increasing social contact and social support have an association with better health behavior [
55,
56], which further results in better health outcomes: reduce the chance of being ill and positively influence the overall frailty and its three domains [
50,
57,
58]. While this study did not study on the amount or frequency of alcohol intake, further studies should explore levels of alcohol intake in relation to frailty and its three domains.
We found that people who engaged in physical activities only once a week or less were more likely to be frail (both overall and its three domains). These results are in line with the results of a previous study [
33]. Previous studies have concluded that physical activities could help older people realize that their bodies can still function well, increase connections with other people [
59] and then decrease the occurrence of depression or depressive symptoms [
60] and further improve their emotional well-being [
61]. Under these mechanisms, physical activities could contribute to a lower risk of overall frailty, and physical, psychological and social frailty among older people.
Smoking was not significantly associated with frailty and its three domains in this study. However, as was stated in previous studies, smoking can damage a range of tissues and organs [
62], and it is associated with diseases such as peripheral vascular disease [
63], coronary heart disease [
64], cancer [
65], respiratory diseases [
66], multiple sclerosis [
67]. All these adverse effects and diseases can negatively influence the physical, psychological and social health of smokers and may lead to frailty [
68,
69]. A potential reason for this might be that we dichotomized smoking into ‘current smoker’ and ‘not current smoking’. It did not consider the amount of smoking or former smoking. Further research is needed to investigate the association between smoking and frailty, including considering the amount of smoking and the smoking history.
Health indicators
In line with previous studies, we found that people who have experienced or currently have at least 2 out of 14 common chronic conditions were associated with a higher risk of being overall frail, and physically and socially frail. Previous studies found that chronic diseases are considered to be major determinants of frailty [
66]. A particular chronic disease could contribute to a specific component of frailty and initiate or worsen frailty [
66]. For example, heart failure and other morbidities accelerate muscle loss, leading to sarcopenia [
70], which further results in rapid functional decline. As has been established, functional decline is closely associated with frailty [
4]. Higher levels of medication risk were associated with higher risks of being overall frail and physically, psychologically and socially frail, which has been confirmed by other studies [
71,
72]. Ageing is associated with an increased prevalence of non-communicable diseases and an increased need for various medications. As a result, an increased risk of inappropriate medication use could occur. Participants who were reported to be malnourished were more likely to be overall frail, and physically, psychologically and socially frail, which is consistent with previous studies [
73,
74]. Unintentional weight loss is one of the items defining frailty [
75]. So, there exist overlap between frailty and sarcopenia [
76]. Muscle mass is low in sarcopenia and poor nutrition may further accelerate loss of muscle mass. This may result in decreasing physical functioning, and further causing adverse outcomes such as falls, infections and pressure sores [
74]. The accumulation of adverse health conditions can result in frailty [
4,
5].
The presence of an interaction effect between sex and household composition on social frailty, indicates that the associations of all studied factors on social frailty varies between different sex as a function of household composition. As previous study have shown [
11], after losing their partner, women more frequently living without a spouse than men. So women are more likely to be engaged in physical activity, but less likely be recognized from potential psychological risks. In addition, women have traditionally played the role of caregiver, may have better life skills, and may not seek care that may be helpful [
77]. It could result in potential undiscovered health problems. However, all these findings could not fully explain the interaction effect of sex and household composition on social frailty. Further studies are needed to clarify this finding.
Limitations and strengths
Our results should be interpreted in the light of some limitations. First, due to the cross-sectional study design, we cannot infer causality. Second, persons were excluded if they lacked the basic knowledge of the local language or if they were not expected to be able to make an informed decision regarding participation in the project. Some of excluded persons might have had a migration background, some might not have been well educated, some might have had a severe health problem. Therefore, our findings may have under-estimated frailty at the population level. Third, we used dichotomous outcome measures of frailty, which may have resulted in loss of information. However, this increases the understanding for practice.
The present study has several notable strengths. First, it is among the few studies that has explored factors of frailty from a multidimensional perspective. We used a validated instrument to consider frailty broadly from the physical, psychological and social domains. Second, the target population is from five diverse European cities. This provides information on this study of a coordinated preventive care approach in various European settings.