Association between stairs in the home and instrumental activities of daily living among community-dwelling older adults

According to a recent report by the United Nations [1], the proportion of people aged 65 or older in the total world population (population aging rate) increased from 5.1% in 1950 to 8.3% in 2015, and it is expected to rise to 18.1% in the year 2060. This indicates that the aging of society will rapidly increase in the latter half of this century. The aging population rate in Japan was 27.3% as of October 1, 2016 [2], and it was the highest in the world.

One of the social issues arising from this progressive ageing of society is the increasing number of older people who need nursing care (i.e., older people in need of nursing). In Japan, the government introduced the public nursing care insurance program in 2000 on the grounds of increasing need for caregiving services and the limitations for family members to give nursing care to other family members due to the changes in family structure [3]. At the time the program started, the number of older people assessed as being in need of nursing care under the public nursing care insurance program was 1.8 million. Since then, it has constantly increased, reaching to 6.2 million in 2015 [4]. It is expected the ratio of old-old people who are 75 or older will increase in the future, which will lead to further increases in the need for nursing care [1, 2].

Once an older person starts to suffer from disability, the decision about whether to live at home or move into a nursing facility becomes important. The rapid increase in the aging population has led to a shortage of nursing facilities for older people. Therefore, Japan and some European and American countries with high population aging rates are promoting home care as an alternative to institutional care as a part of measures to lower social security costs [5, 6]. In view of this social background, it has become a pressing issue to ensure housing stability so that older people can live in a familiar place in their own way until the end of their life, even if they end up needing nursing care. Therefore, studies regarding older people’s housing environments are receiving attention.

Regarding the effects on health of the home environment in older age, especially the impact of the home environment on healthy aging, some researchers have proposed that one of the important indicators is independence in activities of daily living (ADL) [7, 8], and they have reported on the associations between home environment and ADL-related outcomes. For example, Gitlin et al. carried out a randomized controlled trial with a group of older adults aged 70 and over who were not receiving home care services but who had functional difficulties, and reported on a multi-pronged home intervention, which included environmental modifications, and improvements in performing everyday activities, in community-dwelling older adults [9]. Hoenig et al. conducted a study with community-dwelling wheelchair users, and found that more environmental barriers predicted more restriction in daily activities such as medical and non-medical visits [10]. Iwarsson’s study targeted to individuals aged 75–84 living in their own homes, and reported that environmental barriers in the homes were related to ADL dependence [7]. Oswald et al. carried out a survey of people aged 75 to 89 years living alone in their own homes, and demonstrated that very old people living in homes with better accessibility had more independence in daily activities as well as a greater feeling of well-being [11]. These studies’ findings have pointed out that minimizing barriers in the home environment is vital for the older population to maintain their autonomy.

In contrast, recent reports have suggested that, in relation to health effects associated with the home environment, the presence or absence of functional limitations, rather than that of objectively measured environmental barriers, is an important component. For example, Tomsone et al. investigated the relationship between objective and perceived aspects of housing and perceived health among ADL independent and ADL dependent groups of older adults, and reported that persons with ADL dependence tended to have more functional limitations, poorer self-rated health, and poorer perceived housing such as more negative views of their housing situation and less attachment to their home than those without ADL dependence [12]. Ekström et al. studied the differences in the home and health situation between a younger old cohort (i.e., aged 67–70 years) and a very old cohort (i.e., aged 79–89 years), and found that very old people were less likely to live in a dwelling with objectively assessed environmental barriers, but more likely to have functional limitations and report accessibility problems in their housing compared to younger old persons [13]. Kylén et al. investigated objective and perceived aspects of home and health among older adults aged 67–70 living in ordinary houses, and found that all houses had some environmental barriers, but the participants had no problems with accessibility due to good health and functional capacity [14].

According to the World report on disability [15], stairs in a building can become environmental barriers to persons with disabilities and cause activity limitations and participation restrictions. However, if the building incorporates elevators and takes sufficient account of environmental factors by setting barrier-free conditions, activity limitations and participation restrictions can be reduced, as can the limitations to everyday life and social life. Based on the research studies [7, 9‐11] cited above, stairs in buildings are a major environmental barrier to individuals with disabilities, and lead to dependence in ADL. However, based on studies [12‐14], for individuals without disabilities, stairs in a building are unlikely to be a barrier. Instead, stairs in buildings may provide a good opportunity for older adults without disabilities to maintain their physical activity. That is, it is probable that the presence of stairs can create a favorable environment and maintain their functional capacity, which would otherwise deteriorate with advancing age. However, to our knowledge, there has been no study examining whether certain aspects of the home environment are associated with decline or maintenance in functional capacity in community-dwelling older people without disabilities.

We have therefore selected community-dwelling older adults without disabilities at baseline, and conducted a prospective cohort study to test a hypothesis that high-functioning older adults who live in a walk-up residence are less likely to experience a decline in functional capacity.

Baseline characteristics of study participants according to home type are shown in Additional file 1. Subjects who lived in one-storey residences tended to be B Town residents. Subjects who lived in walk-up residences tended to be male, younger, married, working, drinkers, and smokers. Subjects who lived in residences with an elevator tended to have low dietary variety, depression, poor self-rated health, and no participation in social activities. The distribution of self-perceived economic status, BMI, chronic diseases, BADL, and cognitive functioning did not differ with respect to home type.

Baseline characteristics by the presence or absence of IADL decline according to gender are provided in Table 2. Regardless of gender, subjects who had IADL decline were significantly older, more likely to live in B Town, more likely to be underweight, less likely to be habitual drinkers, more likely to have poor BADL, poor cognitive functioning, depression, and poor self-rated health than those without IADL decline. However, the groups did not differ in the distribution of working status, diabetes mellitus, cancer, and smoking history. Men with IADL decline were less likely to have hypertension than men without IADL decline. Women with IADL decline were less likely to be married and poor economic status, were more likely to have cerebrovascular diseases, low dietary variety, and not participate in social activities compared to women without IADL decline.

Table 3 shows the ORs for IADL decline associated with home type according to gender. In Model 1, where the data were adjusted for socio-demographics, health status, and behavioral/physiological/psychological factors, among men, there was no association between home type and IADL decline, while women who lived in walk-up residences were less likely to have a decline in IADL. Significant association in women remained even after additional adjustment for self-rated health and social participation: in Model 2, among men, the ORs for IADL decline were 0.90 (95% CI: 0.71–1.14) in walk-up residences and 0.82 (95% CI: 0.39–1.72) in residences with an elevator. For women, the ORs for IADL decline were 0.72 (95% CI: 0.52–0.99) in walk-up residences and 0.94 (95% CI: 0.49–1.77) in residences with an elevator, compared to those who lived in one-storey residences. Additionally, to explore effect modification by gender, a logistic regression analysis including both “gender” and “the interaction term between gender and home type” was conducted. In Model 2, the results from this additional analysis were not significant (p for interaction = 0.258), suggesting that gender differences in the association between home type and IADL decline were unlikely. Regarding the contribution of the stairs to the decrease in the number of people with IADL decline, the PAF was 3.2% in men and 4.8% in women, suggesting that in this cohort, IADL decline might be preventable in 3.2% of males and 4.8% of females by having stairs in the home.

In this study, we investigated the association between home type and incident decline in IADL. We found that older women who resided in walk-up buildings were significantly less prone to have a 3-year decline in IADL compared to older women who lived in one-storey buildings. Although the mechanisms underlying the association between stairs in the home and IADL change are unknown, we have suggested the following. First, regarding the relation between housing environment and healthy aging, several theoretical approaches have been advocated [39‐41]. In particular, much research has been based on the concept of Person-Environment Fit (PE-fit) [41]. The focus of PE-fit is on interactions and interdependencies between a person and his/her environment; the PE-fit idea assumes that optimal combinations of environmental conditions and person-based competencies can produce the best functioning for that person. As mentioned above, prior studies indicated that the objectively observed barriers in the home environment posed no problem for older adults without functional limitations [12‐14]. Therefore, even if there are the stairs in their home, independent older adults may experience no negative effect on the practice of their daily activities, and have no disadvantage from environmental factors. Indeed, there is a possibility that houses with stairs have a more favorable PE-fit for older people without disabilities than barrier-free housing does. Second, physical inactivity has started to be recognized as the 4th biggest risk factor of human fatalities in the world, and regular physical activity is recommended not only for adults but also children and older people [42]. In so doing, people tend to focus on doing exercises, but it is also recommended to practice and review their daily/lifestyle activities. One guideline on physical activity has cited the following example; “taking the stairs instead of using the elevator, or walking to do errands instead of driving” [43]. Because older people spend more time in their homes compared to younger people [44], going up and down stairs at home may contribute a significant amount of the daily requirement for physical activity, resulting in a positive effect of housing with stairs on functional capacity. In particular, since women are traditionally the main housekeepers, they carry out daily activities like housekeeping, doing laundry, and going out for grocery shopping more than male members of the family [21, 45‐47]. Such activities integrate physical activity into an older female’s daily life, and make a large contribution to their physical activity. Because regular physical activity has a beneficial effect on IADL disability for community-dwelling older persons [48], physical activity that comes from the use of stairs at home may help females maintain their IADL. On the other hand, men didn’t show significantly good effect on their IADL from going up and down stairs at home as women did, because men don’t do housekeeping tasks as often as women. Third, going up and down the stairs makes more demands on respiratory function, builds muscles in the lower leg, and engages greater complexity in neuropsychological organization than walking on flat surfaces and doing light exercises for older people. IADL is a higher-level functional capacity, and it doesn’t only require independent support of physical and cognitive functions but collaboration of each function [49]. The researchers consider that stimulation of muscles and nerve neurons encourages the multiple physical and mental functions required for IADL and leads to IADL maintenance, which is the mechanism matching the use-it-or-lose-it principle.

We need to consider the possibility of reverse causations and confounding factors in this study. First, community-dwelling older adults who were in the preclinical stage of IADL decline may be willing to live in buildings with an elevator. Although the relationship of housing type with BADL and cognitive functioning was not observed, subjects who lived in residences with an elevator were more likely to be older, suffer from depression, have poor self-rated health, and no participation in social activities (data is provided in Additional file 1). Therefore, we cannot dismiss the possibility that people who have a higher risk of developing IADL decline selectively live in buildings with an elevator. Second, because prior studies have demonstrated that regular exercise is positively associated with the maintenance of functioning in older adults [48, 50], we should have asked study participants a question about regular physical activity; our findings have the potential for confounding with fitness habits. Third, although the primary outcome (i.e., IADL) was assessed for both baseline and follow-up surveys, home type was evaluated only at baseline; it is possible that some of the participants’ residences may have been repaired or remodeled during our follow-up period. As home modifications can affect the autonomy of older people [8], it is necessary to conduct a prospective study focused on changes in home type during the follow-up period. Additionally, covariates were only assessed at baseline; we could not consider changing covariates during the follow-up period. Because chronic diseases, cognition, and marital status are identified as significant contributors to IADL in community-dwelling older adults [16, 51], it is possible that these factors impacted IADL if they changed during the follow-up period. However, this study did not take that into consideration. Because the results of this study cannot eliminate the possibility of reverse causation and confounding factors, it is necessary to be cautious when interpreting results.

Our study does not intend to emphasize the beneficial effect of stairs. The docility hypothesis states that people with lower capacity are more vulnerable to the demands of the environment than those with higher capacity [39]. Additionally, a literature search regarding the effects of home environments on disability-related outcomes has indicated that home environmental interventions, such as removing environmental barriers or installing supportive devices, are effective in improving daily activities among functionally vulnerable older adults [8]. Therefore, installing an elevator in a private home may prevent community-dwelling elderly with functional disabilities from being housebound, resulting in benefits to their everyday lives. We also accept that stairs and steps become environmental barriers to people with functional limitations, but in the cases of older people with higher levels of competence, we consider stairs in the home to lead them unconsciously to be more physically active and thereby their functional capacity.

Our study has some limitations. First, the assessment of home type was limited to questions concerning floor level and elevator installation. Previous studies have conducted a detailed assessment of the barriers in homes and accessibility [11, 13, 14]. Furthermore, it has been pointed out that both subjective and objective assessments of the home environment are important [7, 11‐14], but there is no objective data collected for this study. Therefore, our assessment of home type is far from adequate. Further prospective cohort studies are required to confirm our findings by using more detailed and objective instruments to assess home environment. Second, in this study, subjects were asked whether they lived on the 2nd floor or higher in a building and those who answered they did not live higher than the 2nd floor were defined as residents living in one-floor housing. However, there is a possibility that some of those who are defined as living in one-floor housing may live in houses with basements including stairs. Also, there may be one-floor houses with stairs. The researchers cannot deny the possibility that the cohort living in a one-floor house in this study may include people living in a building with stairs. It is unclear whether this issue led to either an overestimate or underestimate of the association between home type and IADL. Third, although this study had a large sample sizes, the majority of older people lived in one-storey residences and the number of people who lived in residences with an elevator was very small. This can cause unstable results, with a wide range of 95% CIs. Additionally, although our study observed a significant association in women between stairs at home and IADL maintenance, its PAF was low (4.8%). The PAF estimate is determined according to the prevalence of cases (in this study, individuals with IADL decline) and the number of people with exposure (in this study, individuals living in houses with stairs). Because women were less likely to have IADL decline and live in walk-up residences than men, this may reduce the impact of stairs at home on IADL in women, leading to a low value of PAF. In the future, our findings need to be replicated in a prospective study in an area where a relatively large number of people live in residences with an elevator or in homes with stairs, for example, a major conurbation. Finally, this study could not yield a high rate of response and follow-up. It is possible that some of those who didn’t participate in the study simply couldn’t because their physical and mental functioning was poor. Regarding subjects who were excluded from this study, their physical and mental functioning were poorer than that of the analyzed subjects (data shown in Table 1). Because cognitive functioning [51] and self-rated health [17] are significant predictors of IADL decline, excluded subjects are considered to be a group at high risk of IADL decline. Additionally, subjects we could not follow-up on may include those who had moved to other dwellings or nursing homes due to a bad housing environment. Hence, subjects who had received a more negative impact of home type on IADL performance may have been selectively eliminated from the survey subjects in this study. These biases may lead to underestimating the association between home type and IADL.

Despite the above-described limitations, to our knowledge, this is the first report to identify an association between home type and IADL of community-dwelling older people with a large-scale prospective cohort study. Although a barrier-free house is recommended for older people, our findings suggest that living in a home with stairs may have the benefit of IADL maintenance for older adults who are functionally independent.