Is female gender a risk factor for Alzheimer's disease?

Despite a growing list of potential new risk factors for Alzheimer’s disease (AD), one of the oldest remains controversial. Is female gender a risk factor for AD? It is likely that the greatest influence on the gender differential in crude prevalence rates is the increasing incidence of dementia with age (Paykel et al., 1994) combined with the greater longevity of women (Moritz & Ostfeld, 1990). This must be distinguished from the hypothesis that there may also be a gender difference in the age-specific prevalence rates of some dementias such as AD. In turn, this could be due to either a higher incidence of dementia in women, or to longer survival times in women followingdiagnosis. What is the evidence for these hypotheses? First, with regard to age-specific prevalence rates, Jorm and colleagues (1987) analyzed 22 dementia prevalence studies carried out between 1945 and 1985. They reported that the overall age-adjusted prevalence of dementia showed no gender difference. When their analysis was adjusted for the specific dementia diagnosis, they found higher rates of AD for women but no difference for multi-infarct dementia. They pointed out that the 22 studies varied widely and that they did not all give age-specific prevalence data, with only 3 studies providing age-specific data for the gender/ diagnosis analysis. Hofman and colleagues (1991) analyzed ageand gender-specific prevalence rates from European studies carried out between 1980 and 1990. They reported a slightly higher rate of dementia in men for subjects under 75 years and a higher prevalence of dementia in women in the 75 years or older age group. More recently, Skoog and colleagues (1993) and Kirby and coworkers (1997) reported no significant gender difference in prevalence rates for AD or ”organic disorders,” respectively. However, three recent studies have reported higher rates in women. In a Chinese community sample, Zhang and colleagues (1990) found a higher age-specific prevalence rate in women for dementia as defined by a cutoff on the Mini-Mental State Examination. Consistent with the analysis of Hofman and coworkers (1991), the Framingham study (Bachman et al., 1992) found a higher age-specific prevalence of both dementia and AD in women compared to men in the 75 years or older age group, whereas Saunders and colleagues (1993) reported higher rates of ”organic disorder” in women for those over 75 years of age but no significant gender difference in younger age groups.