The objective was to examine whether aspects of social relationships in old age are associated with all-cause dementia and Alzheimer's disease (AD).

We studied 1,715 older adults (≥ 65 years) who were dementia-free at baseline over a period of up to 16 years. Data on living status, contact/visit frequency, satisfaction with contact frequency, and having/not having a close friend were analyzed using Cox proportional hazards regressions with all-cause dementia or AD as the dependent variable. To control for reverse causality and to identify potential long-term effects, we additionally performed analyses with delayed entry.

We identified 373 incident cases of dementia (207 with AD) during follow-up. The variable visiting/visits from friends was associated with reduced risk of all-cause dementia. Further, a higher value on the relationships index (sum of all variables) was associated with reduced risk of all-cause dementia and AD. However, in analyses with delayed entry, restricted to participants with a survival time of three years or more, none of the social relationship variables was associated with all-cause dementia or AD.

The results indicate that certain aspects of social relationships are associated with incident dementia or AD, but also that these associations may reflect reverse causality. Future studies aimed at identifying other factors of a person's social life that may have the potential to postpone dementia should consider the effects of reverse causality.

The impact of stressful life events as a risk factor of dementia diseases is inconclusive. We sought to determine whether stressful negative life events are associated with incidental dementia in a population-based study with long-term follow-up. We also tested the hypothesis that the occurrence of positive life events could mitigate or overcome the possible adverse effects of negative life events on dementia conversion.

The study involved 2,462 dementia-free participants aged 55 years and older. Information on life events was ascertained at baseline from a comprehensive Life Event Inventory, which included 56 questions about specific life events. For each life event, the emotional impact (both positive and negative) and emotional adjustment were asked for.

During follow-up, 423 participants developed dementia; of these, 240 developed Alzheimer's disease (AD). Cox regression analysis showed no association between the total number of negative life events and the incidence of dementia when adjusted solely for age and gender (hazard ratio = 0.97, 95% CI = 0.92–1.02), or with multiple adjustments for a range of covariates (hazard ratio = 0.96, 95% CI = 0.91–1.01). Similarly, neither emotional impact nor emotional adjustment to these life events was associated with incident dementia. A separate analysis of AD did not alter the results.

The result of this population-based study finds no association between negative or positive life events and dementia. Accordingly, our results reject the hypothesis that stressful life events trigger the onset of dementia diseases.