Frailty phenotype associated with traffic crashes among older drivers: A cross-sectional study in rural Japan

Highlights

• Prevention strategies towards traffic crashes and physical frailty are urgently needed among the aged population.

• Pre-frail/Frail drivers were significantly associated with increased traffic crashes, compared to robust drivers.

• Frailty intervention programs may not only prevent adverse health outcomes, but also improve driving safety

Abstract

Introduction

In places such as Japan, driving safety and physical frailty are two urgent issues due to a rapidly aging population. However, few studies have focused on whether physical frailty is associated with traffic crashes among older drivers. This cross-sectional study aimed to investigate the association between frailty phenotype and self-reported traffic crashes in the past year among Japanese community-dwelling older adults.

Methods

The sample consisted of 349 community-dwelling older drivers (aged 74.4 ± 5.0 years) enrolled in the Kasama Health Checkup for Longevity survey in rural Japan. The Japanese version of the Cardiovascular Health Study was used to classify participants into a pre-frail/frail group (n = 155, 44.4%) and a robust group (n = 194, 55.6%). Physical and cognitive function were evaluated using performance-based measures, the Geriatric Depression Scale (GDS) was used to evaluate depressive symptoms, and information on risky driving behaviors and traffic crashes was obtained from a self-report questionnaire.

Results

Compared to robust participants, pre-frail/frail participants demonstrated poorer physical function, scored lower on a total five cognitive functions test (5-Cog), and were more prone to depression. Additionally, pre-frailty/frailty (34.2%) was significantly associated with near-miss traffic incidents, compared to robustness (18.0%). Moreover, 46 participants reported involvement in traffic crashes in the past year (33 of 46 were pre-frail/frail). After adjusting for age, sex, total 5-Cog scores, GDS scores, driving distances, and near-miss traffic incidents, pre-frail/frail participants showed higher rates of traffic crash involvement in the past year than robust participants (OR = 3.74, 95% CI: 1.75–7.96).

Conclusion

Frailty phenotype was shown to be associated with an increased rate of traffic crashes. Our findings can be applied to inform health promotion policies and provide timely interventions designed to improve driving safety among pre-frail/frail older adults.

Introduction

As the older adult population rapidly increases in Japan, the number of licensed drivers aged 65 and older has reached approximately 18.2 million (Japanese National Police Agency, 2018), which is 51.7% of the aged population. Consequently, although road traffic crashes in Japan have reportedly decreased, the percentage caused by older drivers—especially those aged 75 years and older—rises annually (Japanese Cabinet Office, 2016). Therefore, prevention strategies are urgently needed to reduce the number of traffic crashes and protect public safety among the aged population.

Another urgent issue associated with the rapidly aging population is the health problem known as frailty (Walston et al., 2006). A consensus of medical professionals has defined physical frailty as a medical syndrome featuring diminished strength, endurance, and reduction of physiologic function. Due to multiple possible causes and contributors, physical frailty leads to increased vulnerability of individuals, high risk of dependency on others, and/or death (Morley et al., 2013). Fried and colleagues (2001) proposed a well-known measurement of frailty phenotype comprising five components: weakness, shrinking (weight loss), slowness, low physical activity, and exhaustion. Frailty is identified by the presence of three or more components, pre-frailty is identified by the presence of one or two components, and robustness (non-frailty) is identified by no components.

Several previous studies reported an association between physical frailty and the driving status of older drivers. A nationally representative longitudinal cohort study showed that frail older drivers had a higher incidence rate for driving cessation over four years than non-frail older drivers (Bond et al., 2017). Another retrospective study comparing characteristics of current older drivers who are frail with those of former drivers showed that advanced age, place of residence (e.g., residential community), and weaker grip strength were independent predictors of driving cessation (Carr et al., 2006). However, few studies have examined the association between frailty and traffic crashes among older drivers. To the best of our knowledge, the only study was a multisite prospective cohort study from the American Automobile Association (Man et al., 2019) demonstrating pre-frailty was associated with a 30% higher risk of at least one self-reported crash in the past year, compared to non-frailty. Contrastingly, no significant association was found between frailty and non-frailty.

Despite these findings from the American Automobile Association, clarification is still needed regarding detailed factors linking frailty phenotype and traffic crashes, which includes health status, physical function using performance-based measures, and general cognitive function (Anstey et al., 2005), presenting a major issue when trying to understand the complexities between physical frailty and driving safety. Additionally, self-reported risky driving behaviors that may subsequently lead to increased risk of traffic crashes, including traffic violations (Factor, 2014) and near-miss traffic incidents (Makizako et al., 2018) also require further examination.

Moreover, although there are several tools to assess physical frailty, the Japanese version of the Cardiovascular Health Study (J-CHS) criteria developed by Satake and colleagues is considered to be the most acceptable assessment tool by Japanese investigators and suitable for Japanese older adults, because two questions of the J-CHS criteria that assess shrinking and exhaustion were adapted from the Kihon- Checklist. The cut-off values for grip strength and gait speed were also modified to suit Japanese older adults. Additionally, two other questions that assess low physical activity were adapted from a previous population-based study conducted on Japanese older adults (Satake et al., 2017). Therefore, it is important to investigate the prevalence of frailty phenotypes as defined by the J-CHS criteria for different characteristics of older adults.

Furthermore, most previous studies regarding Japanese traffic crashes or risky driving behaviors have been limited to urban or suburban areas (Kosuge et al., 2017; Makizako et al., 2018; Matsuoka et al., 2009; Shimada et al., 2016), and have paid less attention to older adults living in rural Japan, although 80.5% of them are current drivers (Abe et al., 2018). Thus, the present study focused on older drivers living in Kasama (population 74,481, area 240.4 km², proportion of older adults 31.6% in 2019), a rural area in Japan, to provide some evidence for research related to traffic crashes among Japanese community-dwelling older adults.

In view of the above, we hypothesized that physical frailty leads to a decline in health status, physical function, and cognitive function, as well as increase in depression, which induces risky driving behaviors in older drivers and subsequently leads to an increased risk of traffic crashes. Thus, the purpose of the present study was to explore the differences in physical and cognitive function and risky driving behaviors across frailty phenotypes, as defined by the J-CHS criteria, and to investigate the association between frailty phenotype and self-reported traffic crashes in the past year among older drivers in rural Japan.