The aim of this study was to determine whether sex differences in cognitive test performance observed in young adults can be observed in a sample of older adults. Our results indicated that the same pattern of sex differences observed in younger individuals was apparent in our cohort. Specifically, women outperformed men on tests of psychomotor speed and verbal learning and memory, whereas men performed better than women on tasks of visuoconstruction and visual perception.
Our finding that sex differences in cognition are apparent in late life suggests that the influence of factors underlying these differences is not attenuated by normal aging. Which factors are most influential in maintaining sex differences in cognitive test performance throughout adulthood remains to be determined, but one possibility is that early-life influences on sexual dimorphisms interact with environmental factors to maintain the differences. Indeed, sex differentiation of the brain is often attributable to the morphological and neurochemical effects of gonadal hormones on brain development. These alterations are thought to lead in some cases to the phenotypic expression of sex differences in adulthood (McEwen, 1983
The notion that organizational, as opposed to activational, effects on brain dimorphism has been suggested to account for why sex differences persist over the lifespan. Results from at least some studies examining the relation between circulating hormones and cognitive functioning, however, would argue against this idea (Puts, Rodrigo, Bailey, Burriss, Jordan, & Breedlove, 2010
). Moreover, preclinical studies have shown that adult hormone manipulations can completely reverse brain sexual dimorphism in some respects (Foy, Chiaia, & Teyler, 1984). Thus, age-related declines on levels of circulating hormones, which appear to have effects on cognition, do not appear to be adequate to diminish the sex differences in cognition that are observed among younger individuals. Examination of sex differences in cognition across the adult-age span is needed to determine whether the magnitude of sex differences in cognition that we observed in this study, while significant, might nevertheless reflect a decrease from that observed among younger adults.
An alternative explanation for why sex differences observed in younger adults are seen among older individuals is that sex differences in other factors associated with cognition emerge in later life. One such factor is vitamin D insufficiency, which has been shown to be more strongly associated with visuospatial skills in women than in men in one study (Seamans, Hill, Scully, Meunier, Androllo-Sanchez, Polito, et al., 2010
) although another study did not find an association between vitamin D levels and visuospatial skills in men or women when assessed with a different test (Menant, Close, Delbaere, Sturkieks, Troller, Sachdev, et al., 2012
). Another factor is the prevalence of white matter disease, which has been shown to be greater in women than in men with advancing age, and has been implicated as contributing to the increased prevalence of dementia in women compared to men (de Leeuw, de Groot, Achten, Oudkerk, Ramos, et al., 2001
). The degree to which other factors affecting cognition become differentially prevalent in men and women with age is an area of future inquiry.
Our finding of a sex difference in cognitive test performance among elderly individuals suggests future studies of cognition among older adults should account for sex. Results from the current study appear to have particular relevance to studies of patients with mild cognitive impairment or frank dementia. Accounting for sex in such studies would maximize the precision with which we can detect cognitive decline, as doing so would increase our ability to detect subtler deficits than we would otherwise be able to appreciate.
This study has several strengths. First, this study represents to our knowledge the largest sample of elderly adults with data from a comprehensive cognitive test battery, which allowed for a comparison of various domains. Second, the men and women in this study were matched for overall level of cognitive functioning, allowing for a comparison of domains of cognition within a sample whose overall level of cognitive functioning was equivalent.
Weaknesses of this study include that it was limited to drivers. This limitation likely restricted the sample to include only those at the higher end of the continuum of cognitive functioning, reducing the representativeness of the sample. However, the fact that our participants may represent the healthier and higher-functioning older individuals may be desirable for our research question, for which we did not wish to have results confounded by sex differences in prevalence of diseases affecting cognition. Nevertheless, we cannot determine whether our results would generalize to individuals who have stopped driving, or to those who have never driven, perhaps for reasons unrelated to health status. Another weakness of this study is that this sample was restricted to one geographic area. Thus, we cannot know whether the cognitive test performance of the participants in this study is representative of those in other geographic locations.