At least in one way, women's brains are better than men's: they age more slowly. Researchers have recently discovered a gene in mice that revitalizes the brains of female mice.
The gene is the same in humans. The finding raises the possibility of preventing cognitive losses in old age for both men and women.
The findings were released in the journal Science Advances on Wednesday. Two further studies on women's brains were also published in the journal: one examined the impact of hormone therapy on the brain, and the other examined how the age of menopause influences the chance of developing Alzheimer's disease.
A gene that delays the aging of the brain
There seemed to be strong evidence that women's brains age more slowly than men's.
By examining how the brain uses blood sugar, researchers have already discovered that older women's brains are metabolically years younger than older men's.
By looking at DNA markers, other researchers discovered that female brains are around a year younger than male brains.
Additionally, women outperformed males of the same age in terms of memory and cognitive ability, according to thorough cognitive examinations of healthy older adults.
To find out why, Dr. Dena Dubal, a neurology professor at the University of California, San Francisco, set out to investigate.
According to Dr. Dubal, "we really wanted to know what could underlie this female resilience." Therefore, she and her colleagues concentrated on the X chromosome, which is the only characteristic that separates males and females. Males have one X and one Y chromosome, while females have two X chromosomes.
In females, one of the X chromosomes shuts down and its genes become almost silent in the early stages of pregnancy. But as people age, Dr. Dubal discovered that silence alters.
She and her colleagues examined the hippocampus, the brain's memory and cognition region, which is damaged by Alzheimer's disease and deteriorates with age.
About the silent X chromosomes, Dr. Dubal stated, "we were astounded to find that genes woke up" when examining aging hippocampal tissue. Although the study was conducted on aging mice, the researchers think the results are relevant to people because mice exhibit the same age-related changes in brain function, with females outperforming males.
Her team concentrated on Plp1, a single awakened gene. According to Dr. Dubal, it produces a protein that is a component of myelin, the fatty covering that surrounds nerve cells and "allows information to flow back and forth, like a highway."
She questioned what would happen if she administered a dose of Plp1 to the hippocampal regions of elderly male mice using gene therapy.
Her group discovered that the mice's memory and cognitive abilities had returned. Dr. Dubal went on to say that they did not even need to transfer the gene to a large number of cells. "Even a small boost made a big difference," she remarked.
Then, even though the female mice were already producing Plp1, she administered the gene therapy to them. Their cognitive abilities and memory improved even further.
"This excites me greatly," Dr. Dubal declared. "Even an elderly brain can become younger and perform better."
Hormone treatment and Alzheimer's
Hormone therapy is used by millions of women to alleviate menopausal symptoms including vaginal dryness and hot flashes, but there are still questions concerning potential brain effects.
The Women's Health Initiative, a major and thorough federal research that was published in 2003, brought attention to the problem when it found that the hormone therapy Prempro, which was then widely used, increased the risk of dementia.
Other researchers have since contended that the danger varies according to a woman's hormone dosage. They believe her brain will be fine if she takes them within ten years of menopause. That opinion is reflected in current treatment standards.
Neuroscientist Rachel F. Buckley of Massachusetts General Hospital and her colleagues gathered 146 healthy women between the ages of 51 and 89 to investigate the effects of hormone therapy on the brain. The women's brains were examined for tau, a protein that builds up in Alzheimer's patients' brains.
Only the women's ages and whether or not they had ever had hormone therapy were known to the researchers. They noticed an effect, which surprised Dr. Buckley.
Tau buildup was higher in women over 70 who had undergone hormone therapy than in those who had not. Although having more tau did not indicate that the ladies had Alzheimer's, it might have set them on the route to developing the condition.
The study found no increase in tau in the brains of women under 70. However, the researchers stated that they were unsure if younger women who used hormones would have higher levels of tau in their later years.
Since the study was observational, causation and effect cannot be established. Uncertainty surrounds the conclusion since the women with higher tau levels may have differed in other ways that the researchers did not take into consideration.
"Talk to your doctor," Dr. Buckley stated when asked what advice she would give women regarding hormone medication and the risk of Alzheimer's disease, although she acknowledged that this was not a suitable response.
Menopause and Alzheimer's disease ages
In another study released Wednesday, the brains of 268 women were compared using autopsy and clinical information. While the others began menopause at the more normal age of around 50, some began early, around 45.
The study's lead researchers found no correlation between age at menopause onset and cognitive deterioration, synaptic integrity, or Alzheimer's disease indicators.
Madeline Wood Alexander, the study's lead author and a doctorate candidate at Toronto's Sunnybrook Research Institute, stated that the findings were "not what we expected." The women who began menopause earlier were expected to have inferior brain functioning, according to the study. According to the authors, this is because estrogen levels, which can shield neurons, fall off throughout menopause.
One correlation that the researchers highlighted as their primary finding was that women who start menopause sooner may have synapses that are more susceptible to Alzheimer's-related alterations as they age naturally.
They stated that when women with early menopause utilized hormone therapy, they did not observe that effect.
The findings conflict with those of the other study, which suggested hormone therapy may raise the chance of brain alterations resembling Alzheimer's. The seemingly incongruous results lacked a clear explanation.
However, the findings on early menopause and hormone therapy were questioned by specialists who were not part of either study. The statistical analysis and models that produced this association, they claimed, did not persuade them.
Studies that examined topics like synaptic vulnerability were hard to understand, according to Dr. Deborah Grady, an emeritus professor of epidemiology and biostatistics at the University of California, San Francisco. "I would like to see the actual incidence of Alzheimer's in these women if menopause timing had an effect," she said.
A similar worry was shared by Dr. Jacques Rossouw, a program officer for the Women’s Health Initiative. He continued by saying that because the authors ran so many statistical tests, it's likely that the association they discovered happened by accident.
"This can't be a big effect if there was no effect of age of menopause on Alzheimer's pathology," he added, even if it is real.
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