Effect Modification on Dietary Patterns on the Relationship Between Slow Gait and Incident Depressive Symptoms: A Six-Year Cohort Study of Older Japanese Adults (NISSIN Project)

Wen Hao^1,2Yi-fan Shan^2,3Takashi Kimura²Shigekazu Ukawa⁴Hideki Ohira⁵Satoe Okabayashi⁶Kenji Wakai⁷Masahiko Ando⁸Akiko Tamakoshi^2*

• ¹School of Public Health, Zhejiang Chinese Medical University, Hangzhou, China
• ²Department of Public Health, Hokkaido Daigaku Daigakuin Igaku Kenkyuin, Sapporo, Japan
• ³The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
• ⁴Osaka Metropolitan University Graduate School of Human Life and Ecology, Osaka, Japan
• ⁵Department of Psychology, Nagoya Daigaku Joho Gakubu Daigakuin Johogaku Kenkyuka, Nagoya, Japan
• ⁶Agency for Health, Safety and Environment, Kyoto Daigaku, Kyoto, Japan
• ⁷Nagoya Daigaku Daigakuin Igakukei Kenkyuka Yobo Igaku, Nagoya, Japan
• ⁸Center for Advanced Medicine and Clinical Research, Nagoya Daigaku Igakubu Fuzoku Byoin, Nagoya, Japan

Background: Slower gait speed is a well-established predictor of late-life depressive symptoms. Prior evidence suggests that diet influences biological processes implicated in both gait decline and depression and may therefore serve as an effect modifier in their associations. This study aimed to examine whether adherence to healthy dietary patterns modifies the relationship between gait speed and incident depressive symptoms in older adults. Methods: In this observational longitudinal cohort study, we analyzed data from 1,887 depression-free, community-dwelling adults aged 64/65 years from the NISSIN Project in Japan. Gait speed was self-rated at baseline as fast, normal, or slow. Dietary intake was assessed using a validated food frequency questionnaire, and principal component analysis identified three dietary patterns: vegetables, fat&meat, and bread&egg. Incident depressive symptoms were defined by a Geriatric Depression Scale score≥6 after a six-year follow-up. Modified Poisson regression was used to estimate relative risks (RRs), and interactions were assessed on multiplicative and additive scales. Results: After six years, 12.5% of participants developed depressive symptoms. Slow gait speed was significantly associated with higher risk of depression (RR: 2.7; 95% CI: 1.6–4.6) , while no dietary pattern was independently associated with depressive symptoms. This risk tended to be lower among slow walkers with higher adherence to a vegetable or bread&egg dietary pattern, although the interactions were not statistically significant. A significant negative interaction was found between slow gait and low adherence to a fat&meat diet on both additive (RERI = –2.5; 95% CI: –4.1 to –0.8) and multiplicative scales (Ratio of RRs: 0.3; 95% CI:0.2-0.3). Conclusion: Dietary patterns may influence the link between slow gait and depression in older adults. Notably, reduced adherence to fat&meat diets was associated with lower combined risk. These findings support dietary improvement as a scalable mental health strategy for physically vulnerable older adults.