Association between education and disability-free life expectancy among Japanese older people: The Ohsaki Cohort 2006 study.

BACKGROUND: Higher education level is associated with longer disability-free life expectancy (DFLE). However, evidence is scarce regarding factors that can contribute to eliminating inequality in DFLE according to education level. This study aimed to clarify the association between education and DFLE and estimate whether DFLE in people with lower education may increase to the same level as that in people with higher education through social participation. METHODS: We analyzed data from 13,849 Japanese people aged 65 years and older who participated in a 13-year prospective study. At baseline, we collected information on education levels (low, middle, or high) and social participation. DFLE was defined as the average duration people expect to live without disability. To calculate DFLE for each education level group, the multistate life table method was employed using a Markov model. RESULTS: At the age of 65 years, DFLE (95 % confidence interval [CI]) in women with low education was 21.3 years (20.8-21.8) without social participation and 24.3 (23.8-24.9) with social participation. In the middle education group, DFLE was 22.1 (21.6-22.6) without social participation and 25.0 (24.6-25.5) with social participation. In the high education group, DFLE was 22.1 (21.5-22.8) without social participation and 25.5 (25.0-26.0) with social participation. Similar results were found for men. CONCLUSIONS: DFLE in people with low or middle education with social participation was almost the same as that in those with high education with social participation, suggesting the possibility that disparities in DFLE by education level could be offset by promoting social participation in older adults.

Psychological distress in later life and incident dementia: The Ohsaki Cohort 2006 Study.

BACKGROUND: The role of reverse causation in the association between psychological distress and incident dementia remains unclear. We investigated whether psychological distress is a risk factor for, or prodromal symptom of, dementia. METHODS: A longitudinal analysis of psychological distress with incident dementia was conducted among 12,076 Japanese individuals (age ≥65 years) followed for 5.7 years. Psychological distress was measured using the Kessler 6-item psychological distress scale (0-24 points) at baseline, with participants categorized into four psychological distress groups: no (0-4), mild (5-9), moderate (10-12), and serious (13-24). Dementia cases were retrieved from the public Long-term Care Insurance database. Cox proportional hazards model was used to estimate the multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (95%CIs) for incident dementia. Stratified analysis was conducted by cognitive function (higher or lower) at baseline. RESULTS: During 60,240 person-years of follow-up, 997 individuals developed dementia. A dose-response association was found between psychological distress and dementia; however, the stratified analysis indicated that this association depended on cognitive function at baseline. Among those with higher cognitive function at baseline, a significantly elevated dementia risk was observed only for serious psychological distress (HR: 2.04, 95%CI: 1.24-3.36). Among those with lower cognitive function, both moderate (HR: 1.30, 95%CI: 1.00-1.68) and serious (HR: 1.79, 95%CI: 1.37-2.34) psychological distress showed an increased dementia risk. CONCLUSION: The association between late-life psychological distress and incident dementia is partly explained by reserve causation, whereby mild and moderate distress could be a prodromal symptom of dementia.