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Open Access Research article

Assessing the association between all-cause mortality and multiple aspects of individual social capital among the older Japanese

Jun Aida12*, Katsunori Kondo3, Hiroshi Hirai3, S V Subramanian4, Chiyoe Murata5, Naoki Kondo6, Yukinobu Ichida3, Kokoro Shirai47 and Ken Osaka2

Author Affiliations

1 Department of Epidemiology and Public Health, University College London, London, UK

2 Department of International and Community Oral Health, Tohoku University Graduate School of Dentistry, Sendai, Japan

3 Center for Well-being and Society, Nihon Fukushi University, Nagoya, Japan

4 Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, USA

5 Department of Community Health and Preventive Medicine, Hamamatsu University School of Medicine, Hamamatsu, Japan

6 Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of the Yamanashi, Chuo-shi, Japan

7 University of the Ryukyus, Naha, Japan

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BMC Public Health 2011, 11:499  doi:10.1186/1471-2458-11-499

Published: 25 June 2011

Abstract

Background

Few prospective cohort studies have assessed the association between social capital and mortality. The studies were conducted only in Western countries and did not use the same social capital indicators. The present prospective cohort study aimed to examine the relationships between various forms of individual social capital and all-cause mortality in Japan.

Methods

Self-administered questionnaires were mailed to subjects in the Aichi Gerontological Evaluation Study (AGES) Project in 2003. Mortality data from 2003 to 2008 were analyzed for 14,668 respondents. Both cognitive and structural components of individual social capital were collected: 8 for cognitive social capital (trust, 3; social support, 3; reciprocity, 2) and 9 for structural social capital (social network). Cox proportional hazard models stratified by sex with multiple imputation were used. Age, body mass index, self-rated health, current illness, smoking history, alcohol consumption, exercise, equivalent income and education were used as covariates.

Results

During 27,571 person-years of follow-up for men and 29,561 person-years of follow-up for women, 790 deaths in men and 424 in women were observed. In the univariate analyses for men, lower social capital was significantly related to higher mortality in one general trust variable, all generalised reciprocity variables and four social network variables. For women, lower social capital was significantly related to higher mortality in all generalised reciprocity and four social network variables. After adjusting for covariates, lower friendship network was significantly associated with higher all-cause mortality among men (meet friends rarely; HR = 1.30, 95%CI = 1.10-1.53) and women (having no friends; HR = 1.81, 95%CI = 1.02-3.23). Among women, lower general trust was significantly related to lower mortality (most people cannot be trusted; HR = 0.65, 95%CI = 0.45-0.96).

Conclusions

Friendship network was a good predictor for all-cause mortality among older Japanese. In contrast, mistrust was associated with lower mortality among women. Studies with social capital indices considering different culture backgrounds are needed.