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Peer-reviewedCC BY 4.0Journal of Epidemiology

Homogeneity and Heterogeneity in Social Networks and Brain Aging in Community-dwelling Older Adults in Japan: The NEIGE Study

  • Hiroshi Murayama1
  • Shiho Amagasa2,3
  • Masaki Machida3
  • Shigeru Inoue3
  • Takeo Fujiwara4
  • Yugo Shobugawa5
5 affiliations
  1. 1Research Team for Social Participation and Healthy Aging, Tokyo Metropolitan Institute for Geriatrics and Gerontology, Tokyo, Japan
  2. 2Teikyo University School of Public Health, Tokyo, Japan
  3. 3Department of Preventive Medicine and Public Health, Tokyo Medical University, Tokyo, Japan
  4. 4Department of Public Health, Institute of Science Tokyo, Tokyo, Japan
  5. 5Department of Active Aging, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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Abstract

Background: As the global population ages, understanding factors influencing structural brain aging is crucial for dementia prevention. Social networks have emerged as important social factors; however, longitudinal evidence linking specific structural characteristics of social networks to brain volume change remains limited. This study examined whether social network homogeneity and heterogeneity were related to longitudinal changes in brain volume (hippocampus, gray matter, and prefrontal cortex) among community-dwelling older Japanese adults.

Methods: Data were obtained from the Neuron to Environmental Impact Across Generations (NEIGE) study. Participants aged 65–84 years were randomly selected from Tokamachi City, Japan. Of the 527 older adults surveyed at baseline, 279 who underwent magnetic resonance imaging at both baseline (2017) and follow-up (2021) were included. Social relationship (dis)similarities were assessed using ten items, and network homogeneity and heterogeneity domains were derived through factor analysis. Covariates included sociodemographic factors, health behaviors, health conditions, and apolipoprotein E genotype.

Results: Participants were 47.6% male, with a mean age of 73.2 (standard deviation, 5.1) years. Multiple linear regression analyses with inverse probability weighting indicated no association between homogeneous social networks and brain volume changes. However, lower network heterogeneity was significantly associated with a greater decline in hippocampal volume. This was particularly pronounced in the right hippocampus.

Conclusion: Greater social network heterogeneity may attenuate age-related hippocampal volume loss in older adults, highlighting potential benefits of social network heterogeneity for structural brain aging and cognitive aging in later life. Further studies are warranted to clarify the underlying mechanisms.

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Cite

BibTeXRIS
BibTeX
@article{murayama2026homogeneity,
  title = {{Homogeneity and Heterogeneity in Social Networks and Brain Aging in Community-dwelling Older Adults in Japan: The NEIGE Study}},
  author = {Hiroshi Murayama and Shiho Amagasa and Masaki Machida and Shigeru Inoue and Takeo Fujiwara and Yugo Shobugawa},
  journal = {Journal of Epidemiology},
  year = {2026},
  month = nov,
  doi = {10.2188/jea.je20250534},
  url = {https://doi.org/10.2188/jea.je20250534},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Homogeneity and Heterogeneity in Social Networks and Brain Aging in Community-dwelling Older Adults in Japan: The NEIGE Study
AU  - Hiroshi Murayama
AU  - Shiho Amagasa
AU  - Masaki Machida
AU  - Shigeru Inoue
AU  - Takeo Fujiwara
AU  - Yugo Shobugawa
PY  - 2026
DA  - 2026/11/05
JO  - Journal of Epidemiology
DO  - 10.2188/jea.je20250534
UR  - https://doi.org/10.2188/jea.je20250534
AB  - Background: As the global population ages, understanding factors influencing structural brain aging is crucial for dementia prevention. Social networks have emerged as important social factors; however, longitudinal evidence linking specific structural characteristics of social networks to brain volume change remains limited. This study examined whether social network homogeneity and heterogeneity were related to longitudinal changes in brain volume (hippocampus, gray matter, and prefrontal cortex) among community-dwelling older Japanese adults.  Methods: Data were obtained from the Neuron to Environmental Impact Across Generations (NEIGE) study. Participants aged 65–84 years were randomly selected from Tokamachi City, Japan. Of the 527 older adults surveyed at baseline, 279 who underwent magnetic resonance imaging at both baseline (2017) and follow-up (2021) were included. Social relationship (dis)similarities were assessed using ten items, and network homogeneity and heterogeneity domains were derived through factor analysis. Covariates included sociodemographic factors, health behaviors, health conditions, and apolipoprotein E genotype.  Results: Participants were 47.6% male, with a mean age of 73.2 (standard deviation, 5.1) years. Multiple linear regression analyses with inverse probability weighting indicated no association between homogeneous social networks and brain volume changes. However, lower network heterogeneity was significantly associated with a greater decline in hippocampal volume. This was particularly pronounced in the right hippocampus.  Conclusion: Greater social network heterogeneity may attenuate age-related hippocampal volume loss in older adults, highlighting potential benefits of social network heterogeneity for structural brain aging and cognitive aging in later life. Further studies are warranted to clarify the underlying mechanisms.
SN  - 0917-5040
SN  - 1349-9092
ER  -