The impact of lifestyles on the occurrence of dementia

Abstract

This thesis explored the impact of different lifestyles in late life on the occurrence of Alzheimer's disease (AD) or dementia. Smoking, vitamin B12 and folate in relation to AD have been extensively studied, but the results are inconsistent. Research concerning the association between dementia and social network or social activities is scarce. All five studies for this thesis were done using data from the Kungsholmen Project, a longitudinal population-based study on aging and degenerative disorders in Stockholm. The population for this Project consisted of all those subjects who were 75 years and older on October 1, 1987, and registered in the Kungsholmen district of Stockholm, Sweden.

The prevalence of AD and dementia was negatively associated with smoking (adjusted odds ratios = 0.6, 95% confidence interval (Cl) = 0.4-1.1 and 0.4-1.0). In contrast, the hazard ratios (HR) and (95% Cl) of incident AD and dementia in relation to smoking were 1.1 (0.5-2.4) and 1.4 (0.8-2.7). Mortality over a 5-year follow-up was greater among smokers in demented (HR = 3.4) than nondemented subjects (HR = 0.8).

Compared with subjects having normal serum levels of both vitamin B12 and folate, subjects with low levels of vitamin B12 (< 150 pmol/L) or folate (<10 nmol/L) had a higher risk of developing AD (RR = 2.1, 95% Cl = 1.2-3.5). The association was even stronger (RR = 3.1, 95% Cl = 1. 1 -8.4) in subjects with good baseline cognition (MMSE > 26). A comparable pattern was detected when low vitamin levels were defined as vitamin B 12:5 250 pmol/L and folate< 12 nmol/L.

An extensive or moderate social network decreased the risk of dementia by 30% (95% Cl = 0.47- 0.97) over a 3-year period. Daily to weekly engagement in mental, social, or productive activity was inversely related to dementia incidence. Adjusted RRs (95% CIs) were 0.54 (0.34-0.87) for mental activities, 0.58 (0.37-0.91) for social activities and 0.58 (0.38-0.91) for productive activities. An active and socially integrated lifestyle, defined as having an extensivelmoderate social network, and high level of participation in social/leisure activities and associations, was related to a lower dementia risk. Compared with the lowest level of activity and integration, the adjusted RR was 0.56 (95% Cl = 0.35-0.89) for low level of activity and integration, 0.34 (0.20- 0.59) for high level of activity and integration, and 0.29 (0.11-0.78) for the highest level of activity and integration.

The conclusions of this thesis are: smoking is not protective for AD or dementia, the cross- sectional association might be due to differential survival. Low levels of serum vitamin B12 and folate may be involved in the development of AD. A clear association was detected when both vitamins were taken into account, especially among the cognitively intact subjects. An active and socially integrated lifestyle such as having a rich social network, frequent participation in stimulating activities, whether physical-, social-, or mental-oriented, might prevent an elderly person from developing dementia or postpone the onset of the disease.