We have known for quite some time that women are more likely to develop Alzheimer’s disease than men. The obvious inference is that women live longer than men, on average (the current average age of death for women is 81 and men 76). Given that age is the biggest risk factor for Alzheimer’s disease, women are more likely to live long enough to show symptoms than men.
But many studies have adjusted for age and it is clear that age is not the cause of this sex difference. Indeed, the risk for Alzheimer’s disease is twice that for women than men aged 70-79 but the same for those 80 and older. There is no clear explanation for this relationship.
Despite having a greater risk for Alzheimer’s disease, another interesting sex difference in memory is that healthy woman typically do better than healthy men on recalling lists of words as evidenced by the age norms for memory tests. A recent study from the Mayo Clinic adds an interesting complication (“Age, sex, and APOE4 effects on memory, brain structure and beta amyloid across the adult life span, 2015, JAMA Neurology, March 16, http://archneur.jamanetwork.com/article.aspx?articleid=2193880).
The study focused on 1246 (1209 aged 50 to 95, 37 aged 30-49) participants in a longitudinal study of aging and memory. All were cognitively “normal.” The variables assessed included, age, sex, APOE4 (the “risk gene” for Alzheimer’s disease), hippocampal volume (the short-term memory structure in the brain that is associated with memory loss), and amyloid (a current marker for Alzheimer’s disease based on PET scan results).
1) Memory worsened between 30 and the 90s – as we all suspected.
2) Hippocampal volume reduced between 30 and 60s and reduced faster after the 60s – presumably the source of the memory inefficiency.
3) There was little amyloid until after age 70 – suggesting that the memory loss of aging was not related to Alzheimer’s disease.
4) The memory loss was greater for men than women after age 40.
5) Hippocampal volume was less in men than women especially beyond age 60.
6) There was no sex difference for amyloids – the findings do not appear to be related to the development of Alzheimer’s disease.
7) APOE status was unrelated to hippocampal volume, memory, or sex at any age.
8) After age 70 those with APOE4 displayed more amyloid than those with E2 or E3.
Obviously the relationship between dementia and sex is complicated. However, these results do fly in the face of the belief that memory loss in older adults is always a sign of Alzheimer’s disease. The best conclusion at this time is that the memory inefficiencies associated with normal aging are different from the memory loss associated with Alzheimer’s disease.