Decrease in the usual walking speed and body fat percentage associated with a deterioration in long-term care insurance certification levels

Introduction

The long-term care insurance (LTCI) system was established in 2000 to support the care of older adults in Japan, which has the largest older population globally. The number of individuals receiving LTCI certification increased from 4,907,000 in 2010 to 6,689,000 in 2020 (Cabinet Office, 2023). The cost of LTCI increased from 3.6 trillion Japanese Yen (US$ 32.7 billion) when the system was introduced in 2000, to 11.7 trillion Japanese Yen (US$ 106.4 billion) in 2019 (Yamada & Arai, 2020). Under the LTCI system, eligible individuals receive long-term care benefits according to seven levels of certification by estimated daily care minutes (Ministry of Health, Labor, and Welfare, 2021). Higher estimated daily care minutes are marked with more severe certification levels, and the maximum benefits covered by the LTCI are higher for severe certification levels. These certification levels are periodically updated. The main services include visiting, commuting, short stay, and nursing homes, and their availability and frequency differ depending on the certification level (Konishi, Inokuchi & Yasunaga, 2024). Therefore, changes in LTCI certification levels reflect the physical and mental functions as well as health status, with significant social and economic implications. As the population ages and the number of people needing long-term care increases, the sustainability of insurance finances becomes a risk. Maintaining and improving the health of those eligible for LTCI to reduce long-term care costs has become an important policy issue (Yamada & Arai, 2020; Konishi, Inokuchi & Yasunaga, 2024).

Previous studies on the factors contributing to LTCI have mainly followed older adults with no applicable LTCI for several years, searching for factors that contribute to the development of new LTCI needs (Shimada et al., 2023; Ashida, Kondo & Kondo, 2016; Shimizu, Ide & Kondo, 2023; Matsumoto & Takatori, 2021). Previous studies analyzing changes in certification levels among LTCI recipients have several limitations regarding the assessment items and target individuals, including analyses focusing solely on basic characteristics (Kumai & Ikeda, 2021; Ohnuma et al., 2016), analyses based on several basic characteristics and one functional assessment (Kamiya et al., 2017), analyses combined participants with no applicable LTCI and those who already had LTCI certification (Kawamura et al., 2021), and analyses of institutionalized residents (Jin et al., 2018). Thus, there exists a lack of studies addressing the factors contributing to changes in LTCI certification-level renewal in terms of sarcopenia assessment, targeting older adults who originally received LTCI certification and required assistance or care while receiving care and living at home. Sarcopenia is a functional decline associated with the loss of skeletal muscle mass and has been a major focus in geriatrics in recent years owing to its strong association with decreased quality of life and increased incidence of falls and fractures (Chen et al., 2020; Beaudart et al., 2015; Yu, Leung & Woo, 2014). In Japan, the prevalence of sarcopenia is 9.9% among older adults with no applicable LTCI, while it ranges 41.7–60.2% among those requiring LTCI, which is extremely high. (Makizako et al., 2019; Kitamura et al., 2021; Kamo et al., 2018; Sawaya et al., 2020). Furthermore, several reports have indicated that older adults with sarcopenia requiring LTCI tend to have severe certification levels, fewer daily steps, and an association between the certification levels and the SARC-F score (Yin et al., 2023; Kitamura et al., 2021; Tsugihashi et al., 2021). Considering this background, frequent assessment of sarcopenia among older adults requiring LTCI is essential in geriatric rehabilitation. Therefore, determining a simple screening method to efficiently predict and detect changes in LTCI certification levels based on sarcopenia assessment and recommending effective rehabilitation interventions to maintain or improve LTCI certification levels is beneficial.

In this study, we hypothesized that sarcopenia-related assessments, which are often associated with negative outcomes, are also associated with changes in LTCI certification levels. Our study aimed to address the following research questions: (1) we explored which sarcopenia-related assessments demonstrate sensitivity to changes in the LTCI certification levels; (2) we investigated which among these assessments, baseline data, or degree of change reflects a shift in the LTCI certification levels; and (3) we sought to establish a cut-off value for these assessments in understanding and predicting changes in LTCI certification levels.

Materials & Methods

Study participants

The participants in this study were users of day care for older adults based on the Japanese LTCI system. Daycare is a rehabilitation service involving transportation. The rehabilitation program comprised muscle-strengthening exercises (using machine training), exercise therapy (employing a stationary bicycle ergometer), guidance on activities of daily living, exercise instructions, and others tailored to an individual’s physical and mental conditions. All participants were assessed for LTCI certification level and sarcopenia at baseline and follow-up (six months later). In accordance with previous studies, the inclusion criteria for this study were participants who used our day care and were able to undergo body composition measurements in a standing position (Sawaya et al., 2022). The exclusion criteria were as follows: no follow-up data, diagnosis of dementia, missing measurements, outliers (weight >100 kg), severely frozen gait, and no renewal of the LTCI certification level between baseline and follow-up. A flowchart of the participants is shown in Fig. 1. Physiotherapists performed all assessments.

Results

This study involved 98 participants, with an age (mean ± standard error) of 78.5 ± 0.8 years, consisting of 51 males and 47 females. Of the 98 participants analyzed in this study, 65 (66.3%), 21 (21.4%), and 12 (12.2%) belonged to the maintenance, deterioration, and improvement groups, respectively. Changes in the LTCI certification levels are shown in the raw data. The breakdown of the deterioration group was as follows: eight individuals experienced a one-stage deterioration, ten experienced a two-stage deterioration, two experienced a three-stage deterioration, and one experienced a four-stage deterioration. The breakdown of the improvement group was as follows: nine individuals experienced a one-stage improvement, two experienced a two-stage improvement, and one experienced a three-stage improvement. Table 1 compares the three groups at baseline. No significant differences among the three groups were observed in sarcopenia-related assessments, age, or body size at baseline; only LTCI certification level (P = 0.004) and intact neurological disease status (P = 0.008) were significantly different. Details of the chronic diseases of the participants is presented in Table S1. The deterioration group showed a significant decrease in the usual walking speed (baseline: 0.64 ± 0.25 m/s, follow-up: 0.53 ± 0.21 m/s, P = 0.008) and body fat percentage (baseline: 29.2 ± 9.9%, follow-up: 27.7 ± 10.3%, P = 0.047) (Table 2). No significant differences were observed between the maintenance and improvement groups.

Tables 3 and 4 show the factors associated with the deterioration of LTCI certification levels based on binomial logistic regression analysis. Changes in the usual walking speed were significantly associated with the deterioration of LTCI certification levels in the non-adjusted (β = −4.558, P = 0.016) and adjusted models (β = −3.964, P = 0.042). Similarly, changes in body fat percentage were significantly associated with the deterioration of LTCI certification levels in the non-adjusted (β = −0.202, P = 0.021) and adjusted models (β = −0.246, P = 0.011). The Hosmer–Lemeshow test result was P ≥0.05 for all these models. For usual walking speed, the post-hoc statistical power was 0.89 in the non-adjusted model and 0.95 in the adjusted model. For body fat percentage, the post-hoc statistical power was 0.86 and 0.99 in the non-adjusted and adjusted models, respectively, which indicated good power. Tables S2 and S3 present the results of the binomial logistic regression analysis using only the deterioration and maintenance groups, excluding the improvement group. The ROC curves are shown in Fig. 2. The cut-off values to discriminate deterioration in LTCI certification levels were −0.14 m/s for change in the usual walking speed (sensitivity 85.7%, specificity 42.9%, AUC = 0.64, P = 0.047), and −1.0% for change in body fat percentage (sensitivity 72.7%, specificity 61.9%, AUC = 0.66, P = 0.029).

Discussion

In this study, handgrip strength, usual walking speed, and skeletal muscle mass, which are essential for assessing sarcopenia, showed that a decrease in usual walking speed over time reflected worsening certification levels, with a cutoff value of 0.14 m/s decrease. Previous studies have searched for factors in the occurrence of new LTCI certification by older adults who are not eligible for LTCI or in the deterioration of LTCI levels by institutionalized residents (Shimada et al., 2023; Ashida, Kondo & Kondo, 2016; Shimizu, Ide & Kondo, 2023; Matsumoto & Takatori, 2021; Jin et al., 2018). Our study is unique in that it focuses on older adults living “at home” while receiving LTCI services–that is, those whose functional ability is between that of healthy individuals who are not eligible for LTCI and those who live in institutions, and uses changes in LTCI certification levels as the main outcome. The three research questions described in the introduction section are discussed below.

Regarding the first research question, among the typical assessments of sarcopenia such as handgrip strength, walking speed, and skeletal muscle mass, usual walking speed was the assessment item that reflected deterioration in LTCI certification levels. Gait disturbance is an important factor in worsening prognosis (Landi et al., 2010), and a positive correlation exists between usual walking speed and life expectancy (Studenski et al., 2011). Usual walking speed predicts future LTCI incidents better than complex walking tasks (Shimada et al., 2023). These studies suggest a significant association between severe illness/need for LTCI and walking speed, supporting the results of this study. Moreover, the usual walking speed has the advantage of being simple and accurate for both the measurer and the examinee. The intraclass correlation coefficients of usual walking speed were 0.903 for a wide age range of 20–79 years (Bohannon, 1997), 0.97 for daycare users (Chan & Pin, 2020), 0.94 for residential care users (Chan & Pin, 2020), and 0.91 even for older patients with dementia (Chan & Pin, 2019), whose reliability was expected to be low. The reliability was high for individuals from various backgrounds. Furthermore, usual walking speed is unlikely to cause errors in the specific direction of fixed and proportional bias, even in older adults requiring LTCI (Sawaya et al., 2021). Walking speed is an essential assessment tool for older adults because it is included in the assessment of frailty, which is multifactorial, and sarcopenia (Chen et al., 2020; Satake & Arai, 2020).

Regarding the second research question, the baseline and follow-up changes in usual walking speed, but not the baseline data, responded to the deterioration in LTCI certification levels. All participants had various disabilities requiring care and support, and had received LTCI certification. In other words, all participants already had a certain degree of functional decline, which may explain why the baseline muscle strength and physical function data were not characterized. In addition, the multivariate analysis showed that a decrease in usual walking speed was significantly associated with the deterioration of LTCI certification levels, even after adjustment. Thus, an intensive rehabilitation intervention targeting older adults requiring LTCI who show a decline in walking speed over time rather than a functional decline at baseline may contribute to preventing deterioration in the LTCI certification levels. Similarly, several studies focusing on changes over time reported that a decrease in usual walking speed is associated with an increased risk of mortality, supporting our findings (Perera et al., 2005; White et al., 2013).

Regarding the third research question, the change in usual walking speed that discriminated deterioration in LTCI certification levels was a decrease of 0.14 m/s. The minimal detectable change (MDC), which indicates the clinically relevant changes in the usual walking speed in older Japanese adults requiring LTCI, has been reported to be 0.18 m/s (Sawaya et al., 2021) and 0.19 m/s (Takada & Tanaka, 2021). A 1-year decrease of 0.10 m/s in the usual walking speed predicts death within 5 years (Perera et al., 2005); additionally, cutt-off of clinically significant interventions in the walking speed in patients with sarcopenia were observed to increase 0.10 m/s (Morley et al., 2011). The “clinically relevant changes” in usual walking speed in the previous and present studies were similar, and thus valid. Applying the cut-off value of 0.14 m/s to the walking distance, the decrease in usual walking speed during this period of deterioration in LTCI certification levels would be 0.56 s for 4 m, 0.7 s for 5 m, and 1.4 s for 10 m. A decrease in usual walking speed can be indicative of potential worsening of disability.Physiotherapists and other rehabilitation professionals should be attentive to these changes in clinical settings.

Finally, a decrease in body fat percentage was also identified as a factor contributing to deterioration in LTCI certification levels. This indicates that a decrease in body fat percentage is more sensitive to deterioration in LTCI certification levels than body weight or SMI. In eight studies that analyzed factors contributing to changes in certification levels among LTCI recipients, body fat percentage was not included as a predictor in all the studies (Kumai & Ikeda, 2021; Ohnuma et al., 2016; Kamiya et al., 2017; Kawamura et al., 2021; Jin et al., 2018; Hayasaka et al., 2018; Kawamura, Kato & Kondo, 2018; Miyagishima et al., 2015). To the best of our knowledge, this is the first study to report the association between changes in LTCI certification levels and body fat percentage. Body fat percentage is a nutritional index that reflects visceral fat mass in older adults (Kupusinac et al., 2017). A high body fat percentage may protect against sarcopenia (Jackson et al., 2012). The body fat percentage peaks at 80 years of age and begins to decline later than the muscle strength and skeletal muscle mass (Jackson et al., 2012; Yoo, Won & Soh, 2022; Makizako et al., 2017). Therefore, it may be a sensitive indicator of the deterioration in LTCI certification levels among older adults who require LTCI.

This study has several limitations. First, we found no factors associated with improvements in the LTCI certification levels. The follow-up period in this study was relatively short. Second, the rehabilitation program in daycare was difficult to adjust because it was tailored to an individual’s physical and mental functional status. Third, this study included only those whose body composition could be measured in the standing position and did not include those who had difficulty maintaining the standing position. Despite these limitations, this study is unique because it follows a transition in levels after LTCI certification, which is difficult to track. The results may help guide multidisciplinary interventions for older adults who continue to live in their home communities while undergoing LTCI.

Conclusions

In conclusion, deterioration in LTCI certification levels was sensitively predicted not by baseline data but by decreases in usual walking speed and body fat percentage over time. The cut-off values were a 0.14 m/s decrease in the usual walking speed and a 1% decrease in the body fat percentage. Multidisciplinary rehabilitation interventions for older adults requiring LTCI who show a decrease in usual walking speed and body fat percentage may contribute to the prevention of worsening LTCI certification levels.

Supplemental Information