The Surprising First Sign of Perimenopause (And it’s not hot flushes!)

Hot flushes may be the poster child for perimenopause, but the earliest whisper of this hormonal shift is often far more subtle – and incredibly easy to dismiss.

According to new research carried out by The Menopause Mandate, brain fog is the most commonly reported first symptom of perimenopause, experienced by nearly one in four women. Fresh data from period tracking app Flo reveals that physical and mental exhaustion (95%), fatigue (93%), and irritability (91%) dominate as the most prevalent overall symptoms. Meanwhile, Menopause Mandate’s Mega Menopause Survey of over 15,000 women found that an overwhelming 86% report brain fog, 70% battle fatigue, and anxiety, panic attacks, low mood, and memory glitches routinely rank as the absolute worst aspects of the transition.

Dr Jo Brown, head of human performance at Nurosym, tells Belle About Town that women frequently attribute these physiological shifts to the relentless pace of modern life.

“One of the challenges of perimenopause is that the changes do not always arrive as one obvious symptom. Hormonal signals are changing, and the nervous system is responding to that changing information,” explains Dr Brown. “Sleep, energy, concentration, mood and the ability to manage demands are all influenced by these systems. When several of these things change together, it is worth looking at the bigger picture rather than assuming that you are simply not coping as well as you used to.”

Crucial to this bigger picture is the autonomic nervous system – the internal control centre regulating involuntary functions like heart rate, digestion, breathing, and stress responses. At its core lies the vagus nerve, a vital highway of the parasympathetic nervous system that orchestrates communication between the brain and body to facilitate rest and recovery.

“Perimenopause does not happen in isolation. Women are still working, caring for families, exercising, trying to sleep and responding to the normal demands of everyday life,” says Dr Brown. “The autonomic nervous system is continually helping the body respond to those demands. The vagus nerve is part of the communication between the body and brain and is involved in processes associated with rest and recovery. That interaction is relevant when we think about sleep, stress and how the body responds after a demanding day.”

BBC Radio 2 presenter Zoe Ball previously opened up about the disorienting impact of perimenopause, describing “crippling anxiety” and panic attacks so severe they compromised her ability to host her radio shows. Dr Brown says that one of the most unsettling aspects for women is finding that routine pressures they once handled with ease suddenly feel overwhelming.

“The demand has not necessarily changed. What can change is the internal state in which you are responding to that demand. During perimenopause, hormonal changes, sleep disruption and stress can all influence how the nervous system is responding,” she says. “That can make a familiar workload, conversation or responsibility feel much harder to manage. It does not mean that your ability has disappeared. It means we need to understand the physiological state in which you are trying to access it.”

To navigate this shift effectively, Dr Brown advises looking for broader patterns rather than treating fatigue, erratic sleep, or cognitive overload as isolated grievances.

“What 25 years working with the world’s best athletes has taught me is the value of preparation,” she says. “We know this transition is coming. Women deserve that same opportunity to prepare.

“I want women to get to know their own nervous system. What does feeling ready look like for you? What changes when you are overloaded – your breathing, muscle tension, concentration or sleep? How easily do you settle after a demanding day or session? Look for patterns over time, rather than judging yourself by one difficult morning or a single wearable score.

“So, for a couple of weeks, look for patterns across sleep, energy, mood, concentration and your menstrual cycle. You do not need an elaborate system. The aim is to understand what is changing and whether those changes are occurring together. Recovery is the process of restoring the body and mind after exertion or stress, helping us replenish energy and cope with future demands. It needs to be treated as part of the process rather than something that happens when everything else is finished. Regular movement, consistent sleep timing, time to wind down and opportunities to reduce physiological arousal can all provide useful cues for the body to settle and recover.”