2.1. Study Population

The present cross-sectional study was based on the Shika Study, which has been conducted in Shika town, Ishikawa prefecture since 2011. The Shika Study included interviews, self-administered questionnaires, and a comprehensive health examination.

Shika town is located in Ishikawa prefecture with a population of 21,061 individuals, of which approximately 40% are elderly (65 years and older) and 56% of individuals are older than 40 years of age. We selected four model districts in Shika town for the study including Horimatsu, Higashi-masuho, Tsuchida and Togi with a population in 2016 of 7183 and 2592 households [32]. The invitation letters to participate in the study were sent to all individuals from 40 years of age between January 2015 to January 2016. The study population of the Shika study consisted of 4121 individuals from 40 years of age. Persons were eligible to participate in the study if they were 65 or older and capable of giving informed consent. The present study was conducted on 1634 elderly participants aged 65 years and older (39.65% of all participants from 40 years of age). Written informed consent was obtained from all participants in the survey. The present study complied with Declaration of Helsinki Guidelines and it was approved by the Ethical Committee at Kanazawa University. The recruitment of subjects is shown in Figure 1.

Participant recruitment chart.