Men’s brains SHRINK by 8pm everyday – before resetting overnight, scientists discover

MEN’S brain shrink rise and fall in volume as hormones ebb and flow throughout the day, a study suggests.

A study that scanned a 26-year-old’s brain 40 times over 30 days indicated that men’s brains shrink by 8pm before resetting overnight.

Researchers from the University of California, Santa Barbara, say this cycle of growing and shrinking coincides with rising and falling levels of steroid hormones: testosterone, cortisol and estradiol.

Study co-author Laura Pritschet – now a postdoctoral scholar in psychiatry at the University of Pennsylvania Perelman School of Medicine – said: “Males show this 70 per cent decrease from morning to night in steroid hormones.

“You can think of it almost like a pulsating rhythm from morning to night,” she told Live Science.

Women’s hormones also fluctuate daily but it’s not as pronounced, as the menstrual cycle simultaneously drives longer-term shifts in hormones, she noted.

Researchers scanned a man’s brain in the morning and evening for a month.

The study, published in The Journal of Neuroscience, found that his overall brain volume decreased throughout the day, as did the thickness of the cortex, the brain’s outermost layer.

The volume of grey matter – which plays a significant role in mental functions, memory, emotions and movement – fell by an average of about 0.6 per cent by each night, researchers found.

Two regions of the cortex, the occipital and parietal cortices, shrank the most. These are involved in visual and sensory processing.

Deeper brain structures, such as the the cerebellum, brainstem and parts of the hippocampus, also saw changes throughout the day.

These parts of the brain are involved in coordinating movement, relaying information between the brain and body, and storing memories.

Though changes in brain structure coincided with the daily ebb and flow of steroid hormones, researchers aren’t yet sure if the hormones are driving the changes.

Study co-author Elle Murata, a doctoral student in psychology and brain sciences at UCSB, told Live Science: “I’m convinced that hormones impact the brain and brain structure.

“But in this study, we can’t say that it’s directly causing it.”

But she said “this is another example debunking the myth that hormones are only relevant for females”.

It comes after separate UCSB research found that ‘pregnancy brain’ is a thing – with scans showing how the brain undergoes a “metamorphosis” in the process of having a baby that lingers years afterwards.

Previous studies have also found that taking hormone replacement therapy (HRT) – which tops up waning levels of oestrogen and progesterone during menopause – can prevent the brain from shrinking as you age and could prevent memory decline over time.

For the more recent UCSB study on men’s brains, the 26-year-old participant underwent brain scans and blood tests every 12 to 24 hours for 30 consecutive days.

At each session, he completed a questionnaire to assess levels of stress, sleep, and his mood.

He also underwent endocrine testing at 7 am or at 8pm – sometimes both – to check how levels of certain hormones in his body varied between the morning and evening.

If endocrine samples were being collected in the morning, the participant had to have fasted – not eaten – for at least eight hours and he wasn’t allowed to have coffee before morning tests.

He also abstained from eating or drinking anything for an hour and a half before evening sessions.

The participant gave a 2ml saliva sample at each session, followed by a blood sample.

As they expected, researchers found that steroid hormones peak testosterone, estradiol, and cortisol all peaked in the morning and fell in the evening.

“Testosterone, estradiol, and cortisol decreased from morning to evening by 61, 38, and 92 per cent, respectively,” they wrote.

This was in parallel to a “significant decrease” in brain volume.

Though they couldn’t pinpoint whether this change in brain volume was caused by the hormones themselves, Dr Murata suggested that “something is happening in the visual networks” as brain regions that process visual information saw notable shrinkage.

But it’s worth noting that this study was only carried out on one person, so it can’t necessarily be applied to a wider population.

Pavel Shapturenka, the 26-year-old UCSB doctoral student whose brain was scanned, told Live Science: “All the information that’s out there highlights the inherent endocrine [hormonal] variability in women.

“I like the counterpoint that we are now highlighting the ways in which men’s endocrine systems are variable,” especially since that variability might affect brain function, he said.

Study authors said that a next step might be to investigate how differences in sleep change the brain.