Research Letter
Abstract
We outlined the characteristics and health status of individuals using a mobile health app, based on a real-world user database.
J Med Internet Res 2025;27:e79109doi:10.2196/79109
Keywords
Introduction
The ME-BYO concept, proposed by the Kanagawa Prefecture in Japan, emphasizes the intermediate “predisease” state (ME-BYO) in health management () [,]. The My ME-BYO Record app, launched in 2017, records health and medication data and tracks physical activity. In 2020, the ME-BYO index was integrated to promote behavioral change by visualizing ME-BYO status () []. Unlike many Japanese mobile health (mHealth) apps from private companies, this app is developed and managed by the local government. Most research on mHealth app use relies on surveys [], as developers rarely share app-collected data. We aimed to analyze user characteristics and health status using real-world data from the My ME-BYO Record app, with findings that may inform strategies to improve user engagement.

Methods
Overview
This study reports selected findings from a project commissioned by the Kanagawa Prefectural Government. Between April 1, 2020, and July 31, 2023, a cumulative total of 186,972 individuals registered as users; 10,239 aged ≥18 years who accessed the ME-BYO index at least once were included in the analysis.
The ME-BYO index is a self-reported 15-item assessment of metabolic, locomotor, cognitive, and mental resilience domains. Scores range from 0 to 100, with higher scores indicating better health [] ().
Differences between 1-time and repeat users were tested using t tests (continuous variables) and chi-square tests (categorical variables). Logistic regression examined the association between engagement (1-time users as reference) and independent variables (sex, age, and domain scores). Analyses were performed using Stata 17 SE (StataCorp). Further details are provided in .
Ethical Considerations
This study was approved by the Institutional Review Board of the Kanagawa Cancer Center (2024Eki-108). Informed consent was waived as only anonymous data were analyzed. No compensation was offered. The My ME-BYO Record app is freely available, and users consent to the Kanagawa Prefectural Government’s Terms of Use upon registration [].
Results
Of 10,239 users, 21.5% (n=2202) were repeat and 78.5% (n=8037) were 1-time users. Repeat users had significantly lower ME-BYO scores (). Logistic regression showed they were older, had lower cognitive function, and higher locomotor function than 1-time users (Table S1 in ).
| Characteristic | ME-BYO index users | P valuea | |||
| 1-time users (n=8037) | Repeat users (n=2202) | ||||
| Sex, n (%) | <.001 | ||||
| Women | 3966 (49.3) | 992 (45) | |||
| Men | 4071 (50.7) | 1210 (55) | |||
| Age (years), mean (SD) | 52.4 (12.8) | 56.2 (11.7) | <.001 | ||
| Age group (years), n (%) | <.001 | ||||
| 18-29 | 441 (5.5) | 56 (2.5) | |||
| 30-39 | 921 (11.5) | 138 (6.3) | |||
| 40-49 | 1625 (20.2) | 361 (16.4) | |||
| 50-59 | 2596 (32.3) | 744 (33.8) | |||
| 60-69 | 1805 (22.5) | 636 (28.9) | |||
| 70-79 | 575 (7.2) | 245 (11.1) | |||
| ≥80 | 74 (0.9) | 22 (1) | |||
| ME-BYO score, mean (SD) | 84.1 (10) | 83.6 (10.1) | .02 | ||
| Metabolic function, mean (SD) | 89.5 (11.4) | 89.1 (11.4) | .13 | ||
| Locomotor function, mean (SD) | 83.6 (21.1) | 85.5 (19.8) | <.001 | ||
| Cognitive function, mean (SD) | 84.3 (23.3) | 80.8 (25) | <.001 | ||
| Mental resilience, mean (SD) | 63.4 (21.4) | 63.5 (21.5) | .97 | ||
aP values were calculated using the t test for continuous variables and the chi-square test for categorical variables.
Discussion
Principal Findings
Approximately 20% (n=2202) of users were repeat users, indicating repeat engagement with the ME-BYO index for health monitoring was low. Although engagement may increase over time, the Prefectural Government may struggle to incorporate the app into regional health strategies until such growth occurs.
Repeat users were older than 1-time users. Users of mHealth apps supporting self-care and chronic disease monitoring also tend to be older than nonusers []. Older individuals may view the free ME-BYO index feature as a useful tool for monitoring well-being, leading to repeat engagement [,].
Repeat users also had lower ME-BYO index scores, particularly in cognitive function. As the app displays the latest ME-BYO index score on the home screen, repeat users may be motivated by disappointment with low scores and continue using the app to improve them []. Conversely, 1-time users might worry that subsequent scores would be worse. Lower cognitive ability has been associated with reduced mHealth access [], yet individuals with chronic conditions are more likely to use mHealth apps than those without []. Our findings suggest that this app may help manage cognitive function in those with poorer cognitive abilities.
Repeat users also had higher locomotor function scores. Physically active individuals are more likely to use mHealth apps to manage health behaviors []. Similarly, those with better mobility may perceive the app as more useful for health monitoring, encouraging active engagement [].
Limitations
First, most app users were aged older than 40 years, limiting the generalizability of our findings to younger age groups. Second, there is potential for reporting bias through self-report. Although the Mini-Cog and walking speed measures in the ME-BYO index have been validated [,], other components still require validation. Third, the dataset lacked details such as disease comorbidities and socioeconomic status, which may affect user engagement. Including these confounders in future studies will improve the interpretation of the findings.
Conclusions
This study highlights a gap between 1-time and repeat engagement with the ME-BYO index for health monitoring. Using a real-world database, our findings may help inform strategies to improve engagement.
Acknowledgments
Data analysis was conducted by the authors as part of a project commissioned by the Kanagawa Prefectural Office. We thank Editage for English language editing.
Data Availability
In accordance with the Act on the Protection of Personal Information, public disclosure of the data is restricted. For details regarding personal data protection and the use of anonymized data, please refer to the Kanagawa Prefectural website.
Authors' Contributions
Writing—original draft: CLC
Writing—review and editing: CLC, SN, KW, and HN
Conflicts of Interest
None declared.
Additional materials on the ME-BYO index, data analysis, and Table S1.
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Abbreviations
| mHealth: mobile health |
Edited by A Mavragani, A Stone; submitted 15.Jun.2025; peer-reviewed by S Kc, E Baker; comments to author 14.Aug.2025; revised version received 25.Sep.2025; accepted 30.Sep.2025; published 10.Oct.2025.
Copyright©Choy-Lye Chei, Sho Nakamura, Kaname Watanabe, Hiroto Narimatsu. Originally published in the Journal of Medical Internet Research (https://www.jmir.org), 10.Oct.2025.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research (ISSN 1438-8871), is properly cited. The complete bibliographic information, a link to the original publication on https://www.jmir.org/, as well as this copyright and license information must be included.

