The year 2003 marked more than one turning point in Oprah Winfrey's life: she became the first Black American woman billionaire, and she reached menopause.
In a recent chat with gal pals Maria Shriver and Drew Barrymore, the queen of daytime talk shows said when she started "The Big M" at age 48, she couldn't focus.
"I remember going through a period where I just ... could not concentrate [on] reading, which is my favourite thing to do," the 69-year-old said.
Menopause is the time in a person's life when their menstrual periods have stopped for 12 months, and marks the end of their reproductive stage.
Most people become menopausal in their mid-40s to around 60, and the transition is preceded by eight to 10 years of "perimenopause", when hormone levels start bouncing around and symptoms emerge.
Around two-thirds will — like Oprah — experience cognitive symptoms such as brain fog and forgetfulness.
Roughly 10 per cent report changes in mood, such as irritability, tearfulness or feeling depressed.
It's important to note that menopause isn't a medical condition — it's a natural process, says Caroline Gurvich, a clinical neuropsychologist and head of the Hormones and Cognition Group at the Monash Alfred Psychiatry Research Centre.
"But while some women don't suffer, others really do," Dr Gurvich says.
"So we need to understand what's going on and why hormones impact the brain, behaviour and thinking so we can help women thrive."
One reason for changes in mood and cognition may be wild fluctuations and an eventual permanent drop in the production of the sex hormone oestrogen.
There are two main types of oestrogen implicated in menopause.
The most potent form we produce is called oestradiol. It is generally made during reproductive years, and can drop by 85 to 90 per cent during menopause.
Then there's a weaker form of oestrogen called oestrone, which decreases by around 65 to 75 per cent.
"They both fluctuate rapidly during perimenopause, and reduce after menopause, but oestradiol reduces the most, which makes oestrone the predominant oestrogen post menopause," Dr Gurvich says.
Oestrogen's influence on the brain
While oestrogen is mostly produced in the sex organs, it influences parts of the body much further afield than the reproductive system, such as the brain.
It can stimulate brain cells in regions responsible for regulating emotions and memory, as well as executive functioning, organisation and decision-making.
Oestrogen can also control which genes are switched on or off.
This means oestrogen — mostly the more potent oestradiol — exerts a whole range of beneficial effects in the brain, such as forging new, and strengthening existing, connections between brain cells; boosting chemicals such as dopamine and serotonin; and increasing the amount of energy our brain cells have available to use.
"We don't really know as much about the role of oestrone in terms of neurobiology and cognition, but we do know that we lose oestrogen overall, and particularly oestrodial," Dr Gurvich says.
"When oestradiol levels fluctuate during the perimenopausal period, and then drop off, the brain is no longer getting that stimulation, and those positive effects are reduced."
What can be done about it?
Menopausal hormone therapy, also known as hormone replacement therapy, is usually the most effective way of alleviating neurological symptoms (as well as other menopause symptoms).
But not all mood and cognitive changes can necessarily be attributed to oestrogen levels bouncing around, then falling away.
When "the change" happens, it can be an incredibly busy time, Dr Gurvich says.
"Many women are stretched and busy and juggling lots of things.
"So even without the hormone factors, sometimes people just get stressed because their lives are really busy: people often have teenage children or older parents, and maybe they're busy and in the prime of their career.
"There's just generally a lot going on for women at the same time that they go through menopause."
Disrupted sleep is also commonly reported during perimenopause and menopause, which can also contribute to general brain fog.
And why some individuals experience menopause symptoms while others sail through symptom-free is still largely a mystery.
"It could come down to genetics that predispose some women to be more sensitive to hormonal brain changes — they really feel it," Dr Gurvich says.
There is some evidence that people who experienced PMS symptoms are also at higher risk of menopausal symptoms.
What about the post-menopause brain?
After making it through perimenopause and menopause, people's mood and cognition tend to stabilise — yet oestrogen levels remain low. Why is this?
For the most part, our brain will adjust to lower oestrogen levels, and many symptoms will ease.
But for some women, this new normal might make them more vulnerable to neurodegenerative conditions.
For instance, two-thirds of Australians with dementia are women. No-one knows for sure why that is, but one theory points the finger at oestrogen.
One of oestradiol's benefits is it has a protective effect on the brain, so take it away and you might increase brain inflammation — something that's implicated in conditions such as Alzheimer's disease, Dr Gurvich says.
"But this is more of a hypothesis at the moment, and an area that's really just starting to be uncovered."
Watch The Truth About Menopause With Myf Warhurst on ABC iview.
