Women's better scores in verbal memory tests may leave Alzheimer's undiagnosed until they are in the more advanced stages of the disease.
According to the Alzheimer's Association's Alzheimer's Disease Facts and Figures report, almost two thirds of Americans with Alzheimer's are women. Of the 5.1 million individuals in the U.S. aged 65 and older with Alzheimer's, 3.2 million are women and 1.9 million are men.
The study - published in Neurology, a journal of the American Academy of Neurology - shows that while women and men may indicate the same problems with metabolizing glucose, which occurs in people with Alzheimer's disease, at the same stage of decline, women perform better than men on verbal memory tests.
"Women perform better than men on tests of verbal memory throughout life, which may give them a buffer of protection against losing their verbal memory skills in the precursor stages of Alzheimer's disease, known as mild cognitive impairment," says study author Erin E. Sundermann, Ph.D., of the University of California-San Diego, who conducted the research while at Albert Einstein College of Medicine in Bronx, NY.
"This is especially important because verbal memory tests are used to diagnose people with Alzheimer's disease and mild cognitive impairment, so women may not be diagnosed until they are further along in the disease," she adds.
Mild cognitive impairment is a condition in which a person has minor problems with their mental abilities such as memory or thinking, and it is an intermediate stage between the expected decline of normal aging and the more serious decline of dementia.
Evidence indicates that mild cognitive impairment sometimes arises from a lesser degree of the same types of brain changes seen in Alzheimer's disease or other forms of dementia.
Women compensate for early brain changes with 'cognitive reserve'
It is not yet possible to accurately predict whether a person with mild cognitive impairment will develop Alzheimer's disease through the use of memory tests, scans, and protein level measurements. However, through diagnosing mild cognitive impairment, people who are at an increased risk of Alzheimer's disease can be offered information, advice, and support.
Sundermann and colleagues used data from 254 people with Alzheimer's disease, 672 people with mild cognitive impairment who exhibited memory problems, and 390 people without memory of thinking problems that were included in the Alzheimer's Disease Neuroimaging Initiative.
All participants received verbal memory skill testing and PET brain scans to visualize how well the brain metabolized glucose - the brain's primary source of energy. Reduced glucose metabolism is a sign of dysfunction in brain cells.
Study participants were read 15 words and asked to repeat them back straight away (immediate recall) and then again after 30 minutes (delayed recall).
The results showed that women who had no, mild, or moderate problems with brain metabolism scored better on the memory test compared with men. However, on examination of participants with more advanced metabolism problems, both sexes scored similarly.
"These results suggest that women are better able to compensate for underlying changes in the brain with their 'cognitive reserve' until the disease reaches a more advanced stage," explains Sundermann.
Women reached impaired scores at a lower metabolism rate than men
The maximum score that can be achieved on the immediate recall test is 75. Memory is considered to be impaired if a person scores less than 37. The delayed recall test has a maximum score of 15, and scores of less than eight are considered to be impaired.
Glucose metabolism rate was analyzed in the temporal lobe, the area of the brain responsible for memory function, relative to glucose metabolism in the cerebellum, the area of the brain where metabolism remains stable with increasing age. Temporal lobe glucose metabolism rate ranges from one to four, with the lower end of the scale indicating heightened brain cell dysfunction.
Findings for the immediate recall test demonstrated that women reached the impaired scores at a lower metabolism rate than men - a temporal lobe glucose metabolism rate of 2.2, compared with 2.6. For the delayed recall test, women reached impaired scores at a glucose metabolism rate of 2.9, compared with 3.7 for men.
"If these results are confirmed, adjusting memory tests to account for the differences between men and women may help diagnose Alzheimer's disease earlier in women."
Erin E. Sundermann, Ph.D.
Limitations of the research include that the study was from one point in time with one set of results and scans, which did not allow for changes to be observed over time. Additionally, the participants may not give an accurate representation of the overall population due to the majority of the study participants being white and well-educated.