Summary: Older women tended to have poorer memory fluidity scores than men of the same age group. However, the reverse was true for younger women. Researchers propose the difference could be a result of younger women having more access to higher education than previous generations.
Improvements in access to education for girls over the last century in the UK are likely to have reduced differences in cognitive ageing between men and women, potentially reducing sex disparities in dementia risk, finds a new large cohort study led by UCL.
Though previous research indicates women are at higher risk of dementia than men, the study, published today in The Lancet Public Health, found that historical inequalities in levels of education were partially responsible for differences in cognitive ageing between men and women, potentially contributing to sex disparities in dementia risk.
Using combined data from the English Longitudinal Study of Ageing (ELSA) and the Whitehall II study, the researchers assessed the impact of education and birth cohort on differences in both ‘memory’ and ‘fluency’ trajectories of 15,924 participants born between 1930 and 1955.
Memory was assessed by asking participants to memorise a list of words and then recall as many as possible within two minutes. Fluency was assessed by asking participants to list as many animals as possible within one minute.
Overall, the team found that women performed better than men on the memory test, with more marked differences found in women born more recently. Furthermore, women were also found to experience slower rates of memory decline than men.
Women were found to have poorer fluency scores than men in the older birth cohort, yet this difference progressively reversed in more recent birth cohorts, with women born between 1946 and 1955 having better scores than their male counterparts. The researchers found that these changes could be partially explained by an increase in education level in women born later; whilst men were more likely than women to have high education level across all birth cohorts, women’s education level increased with each successive birth cohort.
Given that poor performance on memory and fluency tests is strongly associated with dementia, the authors conclude that increases in educational opportunities driving improvements in midlife cognition for women may therefore reduce sex differences in dementia risk for future generations.
Carried out with researchers at the French National Institute of Health and Medical Research, the study is thought the be the first of its kind at this scale to comprehensively assess sex differences in cognitive outcomes that also examines the role of secular (long-term) changes in education.
Lead author, PhD candidate Mikaela Bloomberg (UCL Department of Epidemiology and Public Health), said: “Our findings suggest that among people educated in the first half of the 20th century, gender inequalities in access to education led to lower education levels among women and this likely negatively impacted cognitive ageing and therefore increased the risk of dementia for women. Our study suggests this might change in the future, as disparities in access to education decrease, highlighting the importance of equitable access to education for health, particularly in countries where access to education for women and girls is still limited.”
Co-author, Dr Séverine Sabia, (UCL Department of Epidemiology and Public Health) said: “We cannot definitively conclude at this stage that the differences in dementia risk between men and women will be reduced, because we have only studied two components of cognitive function, and education is not the only factor that influences dementia risk. However, the trend that emerges here suggests increases in access to higher levels of education could result in better cognitive ageing and therefore a reduction in sex differences in risk of dementia in the future.”
Funding: The study funders included the National Institute on Aging, National Institutes of Health; UK Medical Research Council; British Heart Foundation; and National Institute for Health Research.
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Sex differences and the role of education in cognitive ageing: analysis of two UK-based prospective cohort studies
Previous studies have shown an excess risk of Alzheimer’s disease and related dementias among women. Education is thought to have a causal association with dementia onset. We aimed to investigate the role of education in influencing sex differences in cognitive ageing.
We analysed data from two prospective cohort studies in the UK; the English Longitudinal Study of Ageing (ELSA) and the Whitehall II study, to assess sex differences in cognitive performance and cognitive decline by birth cohort (birth year 1930–38, 1939–45, or 1946–55), before and after adjustment for education, and by high and low education level. Memory was assessed using immediate recall, for which data were available from all waves of the ELSA (2002–14) and Whitehall II (1997–2015) studies. Fluency was assessed using a semantic fluency test based on an animal naming task, with data available from all waves of the Whitehall II study and waves one to five (2002–10) and wave seven (2014) of the ELSA study. Cognitive scores were standardised separately in each study based on the mean and SD of the corresponding test among participants aged 50–59 years with secondary education.
15 924 participants were included from the two studies. In pooled analyses, women had better memory scores than men in all birth cohorts, irrespective of adjustment for education (eg, at age 60 years, birth cohort 1930–38, mean difference between sexes [male scores minus female scores] –0·25 SDs [95% CI –0·32 to –0·19] after adjustment for education), and in both education level groups. Memory decline was faster in men than in women (at age 60 years, birth cohort 1946–55, mean difference in 13-year change –0·15 SDs [–0·20 to –0·09]; after adjustment for education –0·14 SDs [–0·20 to –0·08]). Men had better fluency scores than women in earlier birth cohorts and in the low education group (at age 60 years, birth cohort 1930–38, mean difference 0·20 SDs [95% CI 0·05 to 0·36]); but women had better fluency scores than men in later birth cohorts and in the high education group (at age 60 years, birth cohort 1946–55, mean difference –0·17 SDs [–0·24 to –0·10]). No sex differences were observed for fluency decline.
Our findings suggest that decreasing disparities between sexes in education, due to secular increases in educational opportunities, could attenuate sex differences in dementia risk and cognitive decline in the future.
National Institute on Aging, National Institutes of Health; UK Medical Research Council; British Heart Foundation; and National Institute for Health Research.