Why the 'running out of oestrogen' story is wrong

You're still having periods — perhaps irregular ones, perhaps heavier than before — yet you feel like a different person. The mood shifts, the 3 a.m. wakefulness, the brain that seems to run on dial-up: none of it fits the story you've been told, which is essentially that perimenopause is about running low on oestrogen.

That story is incomplete in ways that matter enormously. Oestrogen doesn't simply decline during this transition — it surges erratically, sometimes to above-normal peaks, before eventually falling. The Cleveland Clinic describes the pattern as a hormonal 'rollercoaster', and that image is biochemically accurate. Meanwhile, at least three other axes are shifting at the same time: progesterone begins falling early, often years before oestrogen drops significantly; the pituitary gland floods the bloodstream with follicle-stimulating hormone (FSH) and luteinising hormone (LH) in a compensatory bid to restart uncooperative ovaries; and oestrogen's disruption impairs the body's ability to regulate cortisol, introducing a stress-hormone layer that amplifies everything else.

When the narrative is oversimplified into 'low oestrogen', women are set up to expect a single-variable fix — a switch to be flipped. The biology is a chemistry storm: cascading, interactive, and unique to each woman's physiology. Understanding which hormones are doing what, and why they interfere with one another, is where the real picture begins. The first disruption, almost always, is progesterone.

Progesterone drops first — and takes your calm with it

Each monthly cycle, progesterone is manufactured by the corpus luteum — the temporary structure the ovary builds after an egg is released. No ovulation, no corpus luteum, no progesterone. In the early 40s, as ovulation begins to falter and skip, that production becomes inconsistent, then genuinely low, long before oestrogen makes any dramatic move. It is the quietest part of the perimenopause story, and often the most disruptive.

Progesterone's role is far from purely reproductive. Its principal metabolite, allopregnanolone, binds to GABA receptors in the brain — the same receptors targeted by sedatives and anxiolytic drugs. Think of it as the body's own built-in calming signal: it reduces neural excitability, eases the transition into deep sleep, and takes the edge off the day. When progesterone falls, that signal weakens. The result is not imagined: anxiety that arrives without obvious cause, sleep that becomes lighter or fractured, and a low-grade irritability that feels disproportionate to circumstances.

Because oestrogen may still be circulating at normal or even elevated levels at this stage, the blood panel — if taken at the wrong point in the cycle, or interpreted without context — can look unremarkable. Yet the balance has already shifted. The relative dominance of oestrogen over a depleted progesterone creates a neurochemical environment that is genuinely altered. Periods may still come with reasonable regularity. The body gives little outward signal that anything has changed.

This is the opening act of the transition — a temporary imbalance that, within a few years, becomes the foundation for oestrogen's own turbulent departure.

Oestrogen does not decline smoothly — it surges before it falls

Think of an engine misfiring before it finally stalls. It doesn't run quieter and quieter — it revs unevenly, cuts out, roars back unexpectedly. Oestrogen in perimenopause follows a similar pattern: rather than declining in an orderly downward slope, it swings erratically, surging to above-normal peaks before eventually — over months and years — trending downward. Both Harvard Health and the Cleveland Clinic describe this as a hormonal 'rollercoaster', and that description is mechanistically precise, not merely metaphorical.

This volatility matters because it is the turbulence itself — not simply low levels — that drives many of the most disruptive symptoms. Hot flushes, migraines, breast tenderness, and dramatic mood shifts often spike when oestrogen climbs unusually high or drops sharply, not necessarily when it settles at a low baseline. A woman can feel fine on Tuesday and derailed by Thursday, not because anything has 'gone wrong' psychologically, but because her oestrogen curve has done something entirely unpredictable in between. The symptom chaos is not imagined; it has a biochemical address.

The brain registers this instability and responds. As the ovaries become less reliable at producing oestrogen, the pituitary gland — which normally orchestrates their output — starts shouting louder, releasing larger pulses of follicle-stimulating hormone (FSH) and luteinising hormone (LH) in an effort to provoke a response. This compensatory surge adds another layer of hormonal noise to an already chaotic internal environment. What rising FSH signals about your individual trajectory — and why it matters well beyond reproductive timing — is the subject of the next section.

What rising FSH is doing to your bones right now

FSH has long been treated as a passive readout — a number that confirms the ovaries are struggling. More recent research, including the 2022 PeKnO study published on PubMed, tells a more active story: FSH directly stimulates osteoclasts, the cells responsible for breaking down bone tissue. It does not merely accompany bone loss; it appears to drive it.

The timing makes this finding particularly important. Lumbar spine density can fall at a rate of 1.8–2.3% per year during late perimenopause, and that accelerated loss frequently begins 2–3 years before the final menstrual period. Around one in four women experiences especially severe loss during this window. Critically, this is happening while many women are still having periods, still feeling broadly well, and not yet within reach of a diagnosis that would prompt investigation.

Because FSH rises earlier and more consistently than oestrogen falls, tracking it from the early-to-mid 40s gives a meaningful lead-time advantage — a signal that bone resorption may already be accelerating before the classic oestrogen-decline picture becomes clear on a standard panel. Serial FSH monitoring, alongside oestradiol and markers of bone turnover, is exactly the kind of early-warning approach that sits within the Chemistry pillar of Professor Paul Lee's Regeneration by Design framework: treat the data as a trend to act on, not a threshold to wait for.

Bone health is an area where individual circumstances vary considerably. If you have concerns about bone density or your perimenopausal trajectory, discuss them with a qualified healthcare professional.

The cortisol spiral: stress, sleep, and metabolic shift

The cascade that troubles most perimenopausal women is not a single hormone going rogue — it is one disruption amplifying another. As oestrogen becomes erratic, the body's ability to regulate cortisol, its primary stress hormone, begins to falter. The result is a self-reinforcing loop, not a list of separate problems.

Normally, oestrogen helps modulate the hypothalamic–pituitary–adrenal (HPA) axis, keeping cortisol responses proportionate. When oestrogen fluctuates unpredictably, baseline cortisol tends to rise and nocturnal peaks become more pronounced — fragmenting the sleep architecture that would otherwise allow the body to restore itself overnight. Disrupted sleep then raises cortisol further the following day, which is precisely where the loop closes on itself.

Early evidence suggests that elevated cortisol may also interfere with progesterone receptors, reducing the effectiveness of whatever progesterone remains. This compounds the deficit already in place from irregular ovulation, heightening hot flush frequency and anxiety in the process. The progesterone still present, in other words, may have a harder time exerting its calming influence.

The metabolic shift flows from the same root cause. Oestrogen normally improves insulin sensitivity; as it fluctuates and falls, that protection is progressively withdrawn. Fat storage migrates from peripheral depots toward the abdomen, and this visceral fat is metabolically active — producing pro-inflammatory cytokines that worsen insulin resistance in turn. According to a clinical review in the GREM Journal, this redistribution is hormonally driven, not simply a consequence of ageing or reduced activity, and it meaningfully raises the downstream risk of dyslipidaemia and cardiovascular disease.

Oestrogen also modulates serotonin, dopamine, and GABA pathways — the systems governing mood stability, motivation, and mental calm. Their disruption by erratic oestrogen, compounded by low progesterone, is why brain fog, poor concentration, mood lability, and anxiety tend to arrive together in this period. Validating them as biological changes what women look for, and what they ask for help with.

Designing your chemistry response — the active approach

The picture that emerges from this biology is not a single malfunction but a cascade with a direction — and that direction matters for how you respond. Symptom-led medicine typically waits for the cascade to make itself obvious: sleep deteriorates for months, a panel is run. By that point, several of the loops described above are already running at full speed.

Professor Paul Lee's Regeneration by Design argues for a different posture. Its Chemistry pillar — hormones, inflammation, and the body's internal environment treated as interdependent variables — frames the question not as 'what is going wrong?' but 'what does this system currently look like, and where is it heading?' Applied to perimenopause, that shift in framing is practically significant.

The cascade has a sequence, and that sequence is actionable. Progesterone falls first, FSH rises earliest, bone resorption begins accelerating before oestrogen dips substantially, and the cortisol–insulin–visceral-fat loop is set in motion while periods are still arriving. Tracking FSH, oestradiol, progesterone, cortisol, and fasting insulin at intervals through the early-to-mid 40s turns that sequence into readable signal rather than retrospective explanation. A steadily climbing FSH is informative long before it reaches postmenopausal levels. A rising fasting insulin alongside central fat redistribution flags the metabolic shift in real time — not after it has compounded.

Sleep architecture and anti-inflammatory nutrition matter here, but they work differently when calibrated to a woman's own longitudinal data rather than applied as generic wellness habits. The practical core of the design philosophy is visibility: the transition is biochemically complex and in some respects inevitable, but it is not illegible. Women who build a picture of their hormonal terrain through serial measurement are positioned to notice inflections early and to make timed, informed decisions alongside a clinician — rather than reactive ones prompted by crisis.

Nothing in this article constitutes medical advice. Perimenopause affects every woman differently, and whether hormonal or other therapies are appropriate is a matter for a qualified healthcare professional who knows your individual history.

1. [1] Menopause — Wikipedia. https://en.wikipedia.org/?curid=49611 https://en.wikipedia.org/?curid=49611
2. [2] Hormone Replacement Therapy — Wikipedia. https://en.wikipedia.org/?curid=19526030 https://en.wikipedia.org/?curid=19526030