No major difference in the incidence of dementia between men and women

A new study on the incidence of dementia in England and Wales, published in the forthcoming issue of the open access journal PLoS Medicine, challenges three commonly held assumptions about dementia.

Contrary to widespread views, the study found that there was no major difference in the incidence of dementia between men and women, that the incidence did not fall beyond a certain critical age, and that there was no difference in the incidence across five different sites (three urban and two rural).

Unlike many previous studies, restricted to single sites, this research, funded by the British Medical Research Council, applied a single methodological approach to over thirteen thousand people across five diverse sites. The researchers studied two thousand five hundred people from each site, dividing them into two age groups: those from sixty-five to seventy-four years of age; and those who were seventy-five years of age and older. Dementia incidence, or the number of new cases over a given time, rises with age. However, the study did not support the previous assumption that dementia incidence varied according to sex. The suggestion in the previous literature that incidence may fall again after a certain, critical age, was also not supported by the findings.

There was no convincing evidence of variation across the sites. This puts into question the idea that action to reduce cardiovascular disease will necessarily have an impact on dementia incidence: a proposal that emerged out of previous, single site studies with differing prevalence of cardiovascular disease and other chronic disorders. The results, together with the methodological approach developed for the Medical Research Council's study, will be valuable for the future research on dementia incidence that is needed to inform public health policy.