It has already been established that severe psychological distress is a major risk factor for completed suicide. However, the impact (population attributable fraction; PAF) of moderate psychological distress on completed suicide has not been clarified. The present study investigated the association between various severities of psychological distress and completed suicide. We analyzed follow-up data covering a 7.3-year period (2006-2014) for 43,473 adults (aged ≥ 40 years) participating in a community-based, prospective cohort study. Psychological distress was measured using the K6 psychological distress scale at the baseline. Participants were classified into three groups according to their K6 score (low: 0-4; moderate: 5-12; severe: 13-24). Completed suicide was determined from a Japanese national database. The Cox model was used to estimate hazard ratios (HRs) for completed suicide. The PAFs of moderate and severe psychological distress for completed suicide were also estimated. The multivariate-adjusted HRs (95% confidence interval) for completed suicide were 2.37 (1.49-3.78) among participants with moderate psychological distress, and 4.16 (2.13-8.15) among those with severe psychological distress, relative to those with low psychological distress (P for trend < 0.001). The PAF of the moderate group for completed suicide was 26.8%, whereas that of the severe group was 10.9%. Not only severe but also moderate psychological distress was significantly associated with an increased risk of completed suicide. The PAF of moderate psychological distress for completed suicide was larger than that of severe psychological distress. Public health actions for suicide prevention should focus on moderate as well as severe psychological distress.

Although it has been suggested that the Japanese diet contributes to the longevity of the Japanese population, no study has examined the association between the Japanese diet and survival time. The present study investigated the association between the Japanese diet and survival time. We analyzed 20-year follow-up data from a cohort study of 14,764 Japanese men and women aged 40-79 years. At the baseline survey in 1994, we collected dietary information using a validated 40-item food frequency questionnaire. Adherence to a Japanese diet consisting of nine components (rice, miso soup, seaweeds, pickles, green and yellow vegetables, fish, green tea, beef and pork, and coffee) was assessed in terms of a Japanese dietary index (JDI) score, the total score ranging from 0 to 9. Cox proportional hazards model and Laplace regression analysis were used to estimate the hazard ratios (HRs) and differences in median age at death (50th percentile differences - PDs in age at death) with 95% confidence intervals (CIs) according to the quartiles of the JDI score. During the follow-up period, we documented 4,619 deaths. We observed that a higher JDI score was associated with a lower risk of mortality and longer survival time: In comparison to participants in the lowest JDI score quartile (0-4), the multivariate-adjusted HR (95% CI) of all-cause mortality was 0.91 (0.83-0.99) and the multivariate-adjusted 50th PD in age at death (95% CI) was 10.2 (3.2-17.2) months longer for those in the highest quartile (7-9). Adherence to a Japanese diet is associated with a longer survival time.

To investigate the association of smoking status and years since smoking cessation with the risk of incident dementia among elderly Japanese. We conducted a longitudinal analysis of smoking status and smoking cessation with dementia in prospective cohort study of 12,489 Japanese individuals aged ≥ 65 years who were followed up for 5.7 years. Information on smoking status and other lifestyle factors was collected via a questionnaire in 2006. Data on incident dementia were retrieved from the public Long-term Care Insurance Database. The Cox proportional hazards model was used to estimate the multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for incident dementia. During 61,613 person-years of follow-up, 1110 cases (8.9%) of incident dementia were documented. Compared with individuals who had never smoked, current smokers showed a higher risk of dementia (HR 1.46, 95% CI 1.17, 1.80). Among ex-smokers, the risk for those who had stopped smoking for ≤ 2 years was still high (HR 1.39, 95% CI 0.96, 2.01), however, quitting smoking for 3 years or longer mitigated the increased risk incurred by smokers; the multivariable HRs (95% CIs) were 1.03 (0.70, 1.53) for those who had stopped smoking for 3–5 years, 1.04 (0.74, 1.45) for 6–10 years, 1.19 (0.84, 1.69) for 11–15 years, and 0.92 (0.73, 1.15) for > 15 years. Our study suggests that the risk of incident dementia among ex-smokers becomes the same level as that of never smokers if they maintain abstinence from smoking for at least 3 years.

Although some experimental biological studies have indicated that citrus may have preventive effects against cognitive impairment, no cohort study has yet examined the relationship between citrus consumption and incident dementia. In a baseline survey, we collected data on daily citrus intake (categorised as ≤2, 3–4 times/week or almost every day) and consumption of other foods using a FFQ, and used a self-reported questionnaire to collect data on other covariates. Data on incident dementia were retrieved from the Japanese Long-term Care Insurance database. A multivariate-adjusted Cox model was used to estimate the hazard ratios (HR) and 95 % CI for incident dementia according to citrus consumption. Among 13 373 participants, the 5·7-year incidence of dementia was 8·6 %. In comparison with participants who consumed citrus ≤2 times/week, the multivariate-adjusted HR for incident dementia among those did so 3–4 times/week and almost every day was 0·92 (95 % CI 0·80, 1·07) and 0·86 (95 % CI 0·73, 1·01), respectively (P_trend=0·065). The inverse association persisted after excluding participants whose dementia events had occurred in the first 2 years of follow-up. The multivariate HR was 1·00 (reference) for ≤2 times/week, 0·82 (95 % CI 0·69, 0·98) for 3–4 times/week and 0·77 (95 % CI 0·64, 0·93) for almost every day (P_trend=0·006). The present findings suggest that frequent citrus consumption was associated with a lower risk of incident dementia, even after adjustment for possible confounding factors.