She and her colleagues were prompted in their research by existing studies that seemed to suggest that an older age at menopause — coupled with a longer reproductive life — are linked with better cognitive performance years later.
However, as the study authors explain, those studies did not use a particularly large sample, and neither did they benefit from a group of age-homogeneous participants.
So, Kuh and team set out to rectify this by looking at birth cohort studies. They investigated the data of 1,315 women using the Medical Research Council National Survey of Health and Development in the U.K.
Menopause and memory: Studying the link
As a part of the survey, the women had been clinically followed since birth — that is, since March 1946 — and had at least one cognitive evaluation as adults. Furthermore, the survey included questions about their age at menopause and other aspects of their reproductive health.
At ages 43, 53, 60–64, and 69, the study participants were asked to take verbal memory tests as well as tests for their cognitive processing speed.
The memory assessment consisted of a task in which the participants were asked to recall as many items as possible from a list of 15, and to do so three times. The maximum score achievable in this task was 45 (they scored one point for each word).
Also, the survey included information on whether the women were taking hormone replacement therapy, whether they had had any surgery such as a hysterectomy, their cognitive ability as children, and a few other social factors, such as level of education and their occupation.
All of these factors were accounted for by the researchers in their analysis.
Late menopause may benefit verbal memory
The study revealed that, on average, participants remembered 25.8 words at age 43, a number that declined to 23.3 words by age 69.
But women whose menopause occurred naturally and later in life had higher scores, being able to recall an additional 0.09 words per year. This correlation was not affected by the use of hormone replacement therapy.
Kuh comments on the findings, saying, "The difference in verbal memory scores for a 10-year difference in the start of menopause was small — recalling only one additional word, but it's possible that this benefit could translate to a reduced risk of dementia years later."
However, she adds, "More research and follow-up are needed to determine whether that is the case."
By contrast, no similar correlation between age and memory was noted among women who had surgery-induced menopause. Also, the researchers found no correlation between the age of menopause onset and the women's information-processing capabilities.
Speculating on the possible mechanisms behind the findings, Kuh says, "This difference [between memory skills and processing speed] may be due to the estrogen receptor role, which regulates the gene that codes brain-derived neurotrophic factor."
The brain-derived neurotrophic factor, she continues, "helps to solidify memory formation and storage." Kuh and her colleagues conclude:
"Our findings suggest lifelong hormonal processes, not just short-term fluctuations during the menopause transition, may be associated with verbal memory, consistent with evidence from a variety of neurobiological studies."