Social capital and cognitive decline after a natural disaster
Authors: Akihiko Ozaki, Tetsuya Tanimoto, Claire Leppold, Tomohiro Morita, Kumi Oshima
Journal: The Lancet Planetary Health (2017)

In their Article, Hikichi and colleagues1Hikichi H Tsuboya T Aida J et al.Social capital and cognitive decline in the aftermath of a natural disaster: a natural experiment from the 2011 Great East Japan Earthquake and Tsunami.Lancet Planet Health. 2017; 1: e105-e113Summary Full Text Full Text PDF Scopus (65) Google Scholar report that social capital appeared to buffer the association between experience of the 2011 Great East Japan Earthquake and Tsunami and increased risk of cognitive impairment among older community-dwelling adults in Iwanuma City, Japan. We have three comments. First, 1329 (37%) of 3156 survivors in the study lost relatives and friends after the 2011 disaster, and were analysed conjointly. However, the risk of cognitive decline might have differed depending on who was lost among relatives and friends. For instance, loss of a spouse could be thought to have delivered a more detrimental effect on social capital than loss of friends. Second, although cognitive disability scores were adjusted for sex as a confounding factor, it is unclear whether gender differences in social capital affected the study results. Social capital and social networks might not have been evenly distributed between both genders, as a result of differing opportunities to invest in social capital between men and women, gender-specific socialisation processes, and differential societal expectations with regard to social networking.2Leeves GD Herbert R Gender differences in social capital investment: theory and evidence.Econ Model. 2014; 37: 377-385Crossref Scopus (15) Google Scholar, 3Van Emmerik IIJH Gender differences in the creation of different types of social capital: a multilevel study.Soc Network. 2006; 28: 24-37Crossref Scopus (114) Google Scholar Particularly in a rural Japanese community, such as Iwanuma, the influence of gender differences might be amplified with the preservation of traditional gender roles. Additionally, it has been suggested that widowhood might be associated with increased mortality among Japanese men, but not Japanese women.4Ikeda A Iso H Toyoshima H et al.Marital status and mortality among Japanese men and women: the Japan Collaborative Cohort Study.BMC Public Health. 2017; 7: 73Crossref Scopus (152) Google Scholar As such, loss of a spouse might have had a different effect on physical and cognitive function depending on the gender of the surviving spouse. Finally, changes in household composition after the disaster were not considered. Our recent study suggested that cohabitant children might be a key source of social support among the elderly population in the coastal area of Fukushima, where levels of social capital could have significantly decreased because of a rapid population ageing and depopulation.5Ozaki A Nomura S Leppold C et al.Breast cancer patient delay in Fukushima, Japan following the 2011 triple disaster: a long-term retrospective study.BMC Cancer. 2017; 17: 423Crossref PubMed Scopus (26) Google Scholar Given that the distance between Iwanuma City and our study site is less than 30 km, the observed findings might also be applicable to the residents in the city, which would suggest that the existence of cohabitant children might have mitigated the decline of cognitive function among the elderly residents in the present study. We would be grateful if the authors could comment on these three points. We declare no competing interests. Social capital and cognitive decline in the aftermath of a natural disaster: a natural experiment from the 2011 Great East Japan Earthquake and TsunamiImproved informal socialising and social participation reduces the risk of cognitive decline due to housing damage in the aftermath of natural disasters. Interventions to promote civic participation should be tried to promote cognitive resilience of older survivors. Full-Text PDF Open AccessSocial capital and cognitive decline after a natural disaster – Authors' replyWe thank Dr Ozaki and colleagues for their interest in our paper.1 Regarding loss of a loved one, we separately examined the effects of loss of relatives versus loss of friends on the decline in cognitive function. Neither type of loss was associated with cognitive decline. We note two limitations of our study. First, our survey asked about loss of “close relatives” in the disaster, and we could not distinguish between spouses and other close relatives (such as adult children). Second, we did not inquire on the baseline survey (ie, before the disaster) about the frequency of social interactions between the survivors and the relatives or friends who were lost. Full-Text PDF Open Access