Science

Naoki Hirabayashi, Takanori Honda, Jun Hata, Yoshihiko Furuta, Mao Shibata, Tomoyuki Ohara, Yasuko Tatewaki, Yasuyuki Taki, Shigeyuki Nakaji, Tetsuya Maeda, Kenjiro Ono, Masaru Mimura, Kenji Nakashima, Jun-ichi Iga, Minoru Takebayashi, Toshiharu Ninomiya

Background and Objectives: Epidemiological evidence has shown that social isolation, a low frequency of social contact with others, is associated with the risk of dementia and late-life depressive symptoms. Therefore, we hypothesized that low frequency of social contact may be involved in brain atrophy, and depressive symptoms may play some role in this relationship. We aimed to evaluate the association between low frequency of social contact and the volumes of various brain regions and to assess the extent to which depressive symptoms mediate these relationships from a large population-based multisite cohort study.

Methods: Dementia-free community-dwelling Japanese aged ≥65 years underwent brain MRI scans and a comprehensive health examination. Frequency of contact with non-cohabiting relatives and friends was determined by asking a single question with four categories: everyday, several times a week, several times a month, and seldom. Total and regional brain volumes, intracranial volume (ICV) and white matter lesions volume were estimated using FreeSurfer software. The associations between frequency of social contact and brain volumes per ICV were examined using analyses of covariance. Mediation analyses were conducted to calculate the proportion of the associations explained by depressive symptoms.

Results: We included 8,896 participants. The multivariable-adjusted mean of the total brain volume in the group with the lowest frequency of social contact was significantly lower compared to that in the group with the highest frequency (67.3% vs 67.8%), with a significant increasing trend across the groups (p value for trend