Introduction: The association of lifespan cognitive reserve (CR) with mild cognitive impairment (MCI) remains controversial. We aimed to examine the association of lifespan CR indicator with the risk of MCI and its progression to dementia, taking brain pathologies into account.

Methods: In a community-based cohort study (mean age, 79 years) with annual followup (median, 5.16 years; maximum, 20 years), a cognitively intact group (n = 1182) and an MCI group (n = 420) were identified at baseline. During the follow-up, 611 participants died and underwent autopsies. CR indicator encompassing education, early life to late-life cognitive and social activities were obtained and tertiled.

Results: The multi-adjusted hazard ratio (HR) of MCI was 0.72 (95% confidence interval [CI] 0.58 to 0.90) in the cognitively intact group, and the HR of dementia was 0.66 (95% CI 0.45 to 0.97) in the MCI group for participants with the highest CR indicator (reference: the lowest CR indicator). Among MCI participants with brain pathologies, dementia incidence was about 50% lower in people with the highest CR indicator than the lowest CR indicator.

Discussion: High lifespan CR indicator reduces risk of MCI, and delays its progression to dementia.

Objective: This study aimed to examine the relationship between sleep duration and all-cause mortality, and to assess the role of cognitive impairment, physical disability, and chronic conditions on this association among very old adults.

Design: A prospective cohort study.

Setting and Participants: Within the Chinese Longitudinal Healthy Longevity Surveys, 17,637 oldest-old aged 80-105 years were followed up to 10 years (2005- 2014).

Measures: Data on sleep duration at baseline were based on self-report and were categorized as short (<7 hour), moderate (7-9 hours), and long sleep (>9 hours). Information on cognitive function using the Mini-Mental State Examination (MMSE), physical disability using Activities of Daily Living (ADL), and chronic conditions including diabetes, heart disease, stroke, asthma, and cancer were collected at baseline based on a structured questionnaire. Information about vital status was ascertained and confirmed by a close family member or village doctor of the participant during the follow-up. Data were analyzed using Cox proportional hazards models, with adjustment for potential confounders.

Results: During the follow-up of 10 years, 11,067 (62.7%) participants died. The multivariate-adjusted hazard ratios (HRs) with 95% confidence interval (CI) for mortality were 1.03 (0.98-1.09) for short sleep and 1.13 (1.08-1.18) for long sleep compared with moderate sleep duration. In stratified analysis by cognitive impairment, physical disability, and chronic conditions, the risk of morality was present only among people with MMSE scores <= 24 but did not differ much when stratified by physical disability and chronic conditions. There was a statistically significant interaction between long sleep and cognitive impairment on mortality (P for interaction = .002).

Conclusions and Implications: Long sleep duration is associated with higher risk of mortality in very old adults independently of health conditions. Cognitive impairment may enhance this association. These findings suggest that health practitioners and families should be aware of the potential adverse prognosis associated with long sleep.

Objective

We aimed to examine whether impaired olfaction is associated with cognitive decline and indicators of neurodegeneration in the brain of dementia-free older adults.

Methods

Within the Rush Memory and Aging Project, 380 dementia-free participants (mean age = 78 years) were followed for up to 15 years, and underwent MRI scans. Olfactory function was assessed using the Brief Smell Identification Test (B-SIT) at baseline, and categorized as anosmia (B-SIT <6), hyposmia (B-SIT 6-10 in men and 6-10.25 in women), and normal (B-SIT 10.25-12 in men and 10.5-12 in women). Cognitive function was annually assessed with a battery of 21 tests, from which composite scores were derived. Structural total and regional brain volumes were estimated. Data were analyzed using linear regression and mixed-effects models.

Results

At study entry, 138 (36.3%) had normal olfactory function, 213 (56.1%) had hyposmia, and 29 (7.6%) had anosmia. In multiadjusted mixed-effects models, hyposmia (beta = -0.03, 95% confidence interval [CI] -0.05 to -0.02) and anosmia (beta = -0.13, 95% CI -0.16 to -0.09) were associated with faster rate of cognitive decline compared to normal olfaction. On MRI, impaired olfaction (hyposmia or anosmia) was related to smaller volumes of the hippocampus (beta = -0.19, 95% CI -0.33 to -0.05), and in the entorhinal (beta = -0.16, 95% CI -0.24 to -0.08), fusiform (beta = -0.45, 95% CI -0.78 to -0.14), and middle temporal (beta = -0.38, 95% CI -0.72 to -0.01) cortices.

Conclusion

Impaired olfaction predicts faster cognitive decline and might indicate neurodegeneration in the brain among dementia-free older adults.