P4-001: Skull circumference, leg length and handedness as developmental indicators and their association with dementia in low- and middle-income countries: Evidence from the 10/66 population-based studies

Abstract

Adult head circumference is to some extent a proxy for neurodevelopment. Adult leg length is a recognised marker of nutritional adequacy in the first few years of life. There is a limited literature linking small skulls and short legs to an increased risk for cognitive impairment and dementia in late life. Left handedness may be associated with increased mortality, and both higher and lower intelligence; findings regarding association with late-onset dementia are inconsistent. We set out to estimate the association between skull circumference, leg length, handedness and dementia prevalence in seven low- and middle-income countries surveyed in the 10/66 Dementia Research Group population-based study baseline phase. One phase cross-sectional surveys of all over 65 year old residents (n=15,075) in 11 catchment areas in seven low- and middle-income countries (China, India, Cuba, Dominican Republic, Venezuela, Mexico and Peru). In each centre the core minimum data set included cross-culturally validated assessments of dementia diagnosis (10/66 dementia), anthropometry, and an extensive sociodemographic and risk factor questionnaire. Poisson regression (STATA 9.2) was used to calculate prevalence ratios (PRs) controlling for age, gender, education and family history of dementia. The effects of secular improvement in nutrition (larger skulls and longer legs in younger people) were evident in Latin America, but not in China or India. After adjusting for relevant confounders, we found fairly consistent and independent associations between smaller skulls (pooled PR 1.23, 95% CI 1.05–1.43) and shorter legs (pooled PR 1.54, 95% CI 1.32–1.85) and risk for dementia. Contrary to previous reports, the effect of skull circumference was not modified by educational level, and the effect of leg length is not modified by gender. Neither of the effects seemed to be mediated via family history of dementia. There was no clear or consistent pattern of association between handedness and dementia risk. Since skull circumference and leg length remain stable throughout adulthood into old age, reverse causality cannot explain the findings. Selective mortality is also unlikely. General early life nutritional programming may be relevant to lifetime dementia risk, in addition to neurodevelopment and brain maturation.