・Introduction
Frailty refers to "a condition that lies between good health and the need for long-term care, characterized by declines in physical and cognitive functions." Both the national and local governments in Japan have been implementing policies aimed at extending healthy life expectancy through frailty prevention.
To effectively implement and evaluate frailty prevention initiatives, it is essential to first appreciate the prevalence of frailty. Several studies have examined the prevalence of frailty among older adults (hereinafter, frailty prevalence) in Japan. However, the reported prevalence widely varies across studies. For example, among studies applying the criteria proposed by Fried et al., estimates of frailty prevalence range from 1.5% to 17.9%--a difference of more than 15 percentage points. This variation is likely due to differences in surveyed regions and participant selection methods. Furthermore, as these studies were conducted in specific local areas, frailty prevalence among all older adults in Japan could not be determined.
To address this gap, our research group was the first to determine the frailty prevalence among community-dwelling older Japanese adults nationwide, using data from a representative sample in the National Survey of the Japanese Elderly¹⁾.

・Survey Methods
We used data from the 2012 (Wave 8) National Survey of the Japanese Elderly. This survey, which has been conducted continuously since 1987, is jointly implemented by the Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, the University of Tokyo, and the University of Michigan. Participants are selected through a stratified two-stage random sampling method to ensure that the sample is representative of older adults across Japan.
The study population consisted of 2,206 individuals aged 65 and older who participated in home-visit interviews in the 2012 survey. Frailty was assessed using the criteria developed by Fried et al., which is the most widely used measure internationally²⁾. The criteria include five components: weight loss, exhaustion, reduced physical activity in daily life, weak grip strength, and slowed walking speed (Figure 1).

Figure 1. Five Components of the Frailty Criteria Proposed by Fried et al.
(Source: Healthy Longevity New Guideline Series: "Prevent Frailty with Three Arrows!" Supervised by the Tokyo Metropolitan Institute for Geriatrics and Gerontology, Committee for the Development of Healthy Longevity New Guidelines; Published by Social Insurance Publishers)

The five components were assessed as follows: weight loss was evaluated using the Body Mass Index (BMI); exhaustion was assessed through questionnaire; reduced physical activity was defined as having little or no regular exercise or walking habits; weak grip strength was determined by grip strength measurement; and slowed walking speed was measured through normal gait speed testing.
Participants who met three or more of the five criteria were classified as frail, those who met one or two criteria were classified as pre-frail (a pre-stage of frailty), and those who met none were classified as robust (non-frail).
To calculate the frailty prevalence, we applied weighting based on the 2010 National Census population data to adjust for sex and age differences among respondents.

・Results
Overall, 8.7% of the participants (95% confidence interval: 7.5%-9.9%) were classified as frail, 40.8% (95% confidence interval: 38.7%-42.9%) were pre-frail, and 50.5% (95% confidence interval: 48.4%-52.6%) were robust.
Figure 2 illustrates the frailty prevalence by sex and age. While there was no significant difference between males and females, frailty prevalence increased with age, showing an explicit trend toward higher rates among older participants.

Figure 2. Distribution of Frailty by Sex and Age

How about socioeconomic status? Frailty prevalence tended to be higher among individuals with fewer years of education and lower household income (Figure 3).

Figure 3. Distribution of Frailty by Socioeconomic Status

When comparing regional blocks, a general "west-high, east-low" pattern was observed; that is, frailty prevalence tended to be higher in western Japan and lower in eastern Japan (Figure 4).

Figure 4. Distribution of Frailty by Regional Block

Finally, what is the extent of impact of frailty on future health outcomes? In an analysis using data collected five years after the initial survey, outcomes such as all-cause mortality, hospitalization or admission to long-term care, and the onset of disability in basic activities of daily living (impairments in essential daily activities such as walking, eating, bathing, and toileting) were examined. The results suggested that, compared to the robust group, those who were frail had worse prognosis in all categories (Figure 5). Although previous studies have reported an association between frailty and poor prognosis, this nationwide analysis reconfirmed that frailty increases the likelihood of mortality and functional decline.

Figure 5. Association between Frailty and Prognosis

・Significance of the Study
This is the first study in Japan to elucidate the prevalence of frailty among community-dwelling older adults. The findings serve as a reference for evaluating frailty prevention measures and for advancing academic research on frailty.
A similar study conducted in the United States using the same methodology reported a frailty prevalence of 15.3% among older adults³⁾. Considering that frailty is linked to higher risks of mortality and poor prognosis, Japan's longer average life expectancy and healthy life expectancy may be partly explained by its lower frailty prevalence.
Moreover, by visualizing regional differences in frailty prevalence in addition to individual characteristics such as sex, age, and socioeconomic status, this study underscores the need to address health disparities across regions.

・References
1. Murayama H, Kobayashi E, Okamoto S, et al. National prevalence of frailty in the older Japanese population: Findings from a nationally representative survey. Archives of Gerontology and Geriatrics, 2020, 91, 104220.
2. Fried LP, Tangen CM, Walston J, et al. Frailty in older adults: Evidence for a phenotype. Journals of Gerontology, Series A: Biological Sciences & Medical Sciences, 2001, 56, M146-156.
3. Bandeen-Roche K, Seplaki CL, Huang J, et al. Frailty in older adults: A nationally representative profile in the United States. Journals of Gerontology, Series A: Biological Sciences & Medical Sciences, 2015, 70, 1427-1434.