Potentially modifiable risk factors for dementia: Evidence from identical twins

Background: A variety of potentially modifiable risk factors over the lifespan have been shown to be associated with dementia in late life. Studying such factors in twins permits testing their importance while controlling for genetic influences. Objective: To test the following potentially modifiable risk factors among twin pairs discordant for dementia: level of education, relative height (as an index of early nutrition), periodontal disease experienced before early adulthood (as an index of inflammatory exposure), participation in mentally stimulating activities in middle adulthood, blue collar occupation, participation in physical exercise in middle adulthood, and history of stroke (as an index of vascular risk factors). Methods: All monozygotic (MZ) twin pairs in which one or both twins were demented were ascertained from the entire Swedish Twin Registry. There were 109 discordant pairs in which information was available from both members of the pair. Pairs were compared using matched t-tests for continuous variables and conditional logistic regression for categorical variables. Conclusion: The demented twins in discordant pairs had significantly fewer years of education (p=.04) and were three times more likely to be the twin with lower education; were four times more likely to have periodontal disease by midlife (p=.008); and were six times more likely to have had a stroke (p=.004). Fifty-six percent of the dementia cases in discordant pairs had one or more of these risk factors. None of the other variables added significantly. Multivariate analyses show that periodontal disease and stroke each contributed significantly to predicting dementia, while partially accounting for the effect of education. Because the analyses involve monozygotic twins, genetic influences are controlled; there were no significant interactions with whether the pair carried an apolipoprotein e4 allele. The results support the view that preventive measures earlier in the lifespan can contribute to lowering the risk of dementia.