I want to start with something I’ve been sitting with for a while.
There’s a particular kind of frustration that I think is almost universal among women navigating perimenopause, and I’ve been trying to put words to it accurately. It’s not the frustration of not knowing what to do. It’s not the frustration of being dismissed or not taken seriously, though both of those are real too.
It’s the frustration of knowing what to do, doing it consistently, and watching it not produce the results it used to produce.
I see this pattern constantly. Women who have done the work - who have genuinely, substantively changed their habits and felt the difference - who then hit their mid-to-late 40s and find the same approaches producing less consistent results. The sleep that had improved becoming fragmented again. The energy that had stabilised becoming unpredictable. The morning clarity that was coming back retreating into fog.
And the worst part isn’t even the symptoms themselves. It’s the loss of trust in your own efforts. The quiet, eroding sense that maybe it was never really working. Maybe you’ve been fooling yourself.
I want to address that directly, before anything else: no, you haven’t been fooling yourself. The strategies were working. The ground changed.
What oestrogen was quietly doing
Most of us learn about oestrogen in the context of reproduction — cycles, fertility, bone density, cardiovascular health. All real, all important. What almost nobody mentions is that oestrogen also plays a direct role in how your master circadian clock functions.
Your circadian clock — the suprachiasmatic nucleus, a tiny structure in your hypothalamus — is the central coordinator of everything that runs on a 24-hour cycle. Your cortisol timing. Your melatonin production. Your body temperature rhythm. Your metabolism. Your immune maintenance. All of it timed by this structure.
Oestrogen receptors are densely expressed throughout this structure. Oestrogen influences the expression of the core clock genes — the molecular machinery that keeps the rhythm running. It affects how robustly the clock responds to the morning light signal. It modulates the amplitude of the daily cycle — how pronounced the peaks and troughs are.
Think of your circadian clock as a pendulum. A well-functioning pendulum swings at full amplitude — clear, consistent, reliable. Oestrogen has been part of what keeps that pendulum swinging at full amplitude. When oestrogen starts to decline — and in perimenopause, it doesn’t decline smoothly, it fluctuates wildly before eventually falling — the pendulum loses some of that support. The rhythm doesn’t stop. But it dampens. The peaks are less pronounced. The troughs less pronounced. The whole system less crisp, less able to absorb disruption without losing its anchor.
This is the mechanism. Not your hormones making you feel bad. Your body clock losing some of its internal stabilisation and becoming proportionally more dependent on external signals to stay anchored.
The three places you’ll feel it
There are three specific ways this plays out, and they tend to compound each other.
The first is the cortisol awakening response — the sharp morning peak in cortisol that provides your initial energy and sets up the hormonal cascade for the rest of the day. Oestrogen influences how robustly this fires. When oestrogen is less stable, the cortisol awakening response becomes variable. Some mornings it fires well. Some mornings it’s blunted. Some mornings it fires at the wrong time — too early, which is why some women wake at 3am feeling alert when they don’t want to be. The maddening thing is the variability. Not consistently bad, but unpredictable — which is harder to work with than consistent.
The second is melatonin. Oestrogen influences the sensitivity of the pineal gland to the light-dark cycle and the timing and amplitude of the melatonin rise in the evening. When oestrogen declines, melatonin production can become less robust — the evening rise flatter, the peak lower, the duration shorter. This feels like not being able to fall asleep despite genuine tiredness. Waking in the night and lying there. Waking earlier than you want and not feeling rested. Not classic insomnia — something more fragmented, more variable, more resistant to the usual fixes.
The third is temperature regulation. Oestrogen affects the thermoneutral zone — the range of body temperatures within which your brain doesn’t trigger a strong cooling or heating response. When oestrogen declines, that zone narrows. Small temperature fluctuations that were previously tolerated without a response now cross the threshold. Your body tries to cool down aggressively. That’s a hot flush. At night, that’s a night sweat that wakes you at the exact point in your sleep cycle when the melatonin that should keep you asleep is already less robust.
These three mechanisms feed into each other. Fragmented sleep affects the cortisol response the next day. A dysregulated cortisol response elevates evening cortisol, which suppresses melatonin, which worsens sleep the following night. The loop runs in all directions simultaneously.
Why your strategies seem to have stopped working
This is what I most want you to understand, because I think it’s the insight that changes how you feel about your own efforts.
The morning light is still working. The meal timing is still working. The evening light management is still working. The signal is still reaching your circadian clock and doing what it’s supposed to do.
But the system receiving that signal has less internal resilience than it used to have. The clock has lost some of its oestrogenic support, which means the external signals you’re providing are having to carry more of the stabilising load. The threshold for what counts as ‘sufficient’ has moved.
The analogy I find most useful: you’ve been watering a plant and it’s been thriving. Then the soil conditions change in a way that makes the roots less able to absorb water efficiently. You’re still watering it. The water is still reaching the roots. But less of it is being taken up. You haven’t done anything wrong. The conditions changed.
What this means practically is that the same strategies that required mostly-consistent effort before now require genuinely non-negotiable consistency. Not more strategies. Not a different approach. The same foundations, applied with less willingness to let things slide when life gets demanding.
Because here’s what I notice: the women who struggle most during perimenopause are often doing everything right in the calm periods and letting the foundations go the moment life gets demanding. Which, during perimenopause, the system can no longer absorb the way it used to. The buffer is smaller. The recovery from disruption takes longer.
What this does not mean
I want to be clear about something. This is not about doing more. It’s not about adding protocols to an already full life. And it is emphatically not instead of HRT if that’s something you’re considering — that’s a separate conversation between you and your doctor, and for many women it’s entirely appropriate.
What I’m saying is that the circadian foundation matters regardless of what else you decide to do. The women who navigate perimenopause most smoothly, in my observation, tend to be the ones who have made a small number of foundational things genuinely non-negotiable. Morning light. Consistent meal timing. A real wind-down in the evening. Some form of deliberate nervous system recovery. Not more than that. But those things, consistently, even when life is demanding. Especially when life is demanding.
What I haven’t told you
I want to be honest about something. What I’ve described in this newsletter — and in Episode 7 — is the mechanism. Understanding it is genuinely useful, because it shifts you from self-blame to accurate diagnosis.
But knowing the mechanism is one thing. Knowing how to implement the right interventions, in the right sequence, for your specific situation — including where you are in the perimenopausal transition, what your sleep looks like, what your cortisol pattern seems to be, what your meal timing currently is — that’s a different level of work.
I see women plateau not because the approach is wrong, but because they’re implementing things in the wrong order, or inconsistently, or without the troubleshooting that’s needed when one pillar affects the others in unexpected ways.
For now: if you want to see how all four pillars work together — light, nutrition timing, metabolic flexibility, and movement — the free masterclass at francesnorgate.com/masterclass walks through exactly that. It’s the full picture in one place.
Your capability hasn’t declined. Your signals are off. And signals can be corrected.
See you next week,
Frances
