More than hot flushes: perimenopause as a systemic shift

The knees that ache on the way downstairs. The morning meeting where the words feel just out of reach. The workout that used to take a day to recover from that now takes three. Many women in their mid-forties notice these changes and chalk them up to a busy life or the inevitable creep of age — and move on.

But research published in the Journal of Neuroinflammation in 2020 by McCarthy and colleagues offers a more specific explanation. Perimenopause, they argue, is not simply a reproductive transition marked by fluctuating hormones and an eventual last period. It is a systemic inflammatory phase — a body-wide shift in how the immune system operates, with consequences that reach well beyond the ovaries into joints, brain, blood vessels, and beyond.

This reframing changes everything about how the experience is understood. Joint stiffness, mental fog, disrupted sleep, and slow recovery are not random complaints of middle age. They may be connected signals from a system under measurable physiological stress. Understanding that mechanism — what is actually happening at a cellular level — is where practical levers begin to appear.

Oestrogen's role as the body's molecular brake

Think of oestrogen as a molecular thermostat for the immune system — one that keeps inflammatory output calibrated to actual need. When it is present at healthy levels, it actively suppresses a key signalling pathway called NF-κB: the transcription factor that tells immune cells to produce pro-inflammatory compounds such as TNF-α and IL-1β. With that brake engaged, the body's inflammatory response stays proportionate. When oestrogen declines, the brake releases — and the immune system runs hotter than the situation warrants.

The mechanism works through two receptor types. ER-α is found across many tissues; ER-β is more specific, governing the inflammasome (the innate immune system's rapid-response unit) and neuronal mitochondrial function. It is ER-β's activity that most directly links falling oestrogen to the inflammatory patterns of perimenopause.

A second layer compounds the first. Macrophages — the white blood cells that normally coordinate tissue repair — carry their own oestrogen receptors. When oestrogen drops, these cells shift from repair-and-resolve mode into a pro-inflammatory state, releasing cytokines that damage rather than rebuild. The immune system is therefore dysregulated at two scales simultaneously: the molecular pathway and the innate immune cells that patrol every tissue in the body.

Worth noting: estradiol is not the only hormone in decline during this transition. Progesterone and testosterone also fall, each contributing to the overall shift. The inflammatory consequences of oestrogen loss are, however, the best-evidenced of the three, which is why it anchors most of what follows.

Where inflammation lands: joints, brain, and bloodwork

Joints are perhaps the most immediately noticeable place to feel it. Cartilage, synovial tissue, and bone all carry oestrogen receptors, so when levels fall, inflammation rises in these structures. The resulting stiffness — most often in the back, hips, and knees — is frequently attributed to stress, overuse, or even fibromyalgia, when the hormonal contribution may be the more direct explanation. Sustained, that low-grade joint inflammation raises the risk of both osteoarthritis and osteoporosis.

The brain registers the shift differently. Microglia — the brain's resident immune cells — are normally held in a low-activity state by oestrogen; without it, they become more readily activated, generating the neuroinflammation that many women recognise as brain fog: blunted recall, the mid-sentence pause, the sense that thinking takes more effort. Vegeto and colleagues (2008) link this chronic microglial activation to longer-term vulnerability to neurodegenerative conditions including Alzheimer's and Parkinson's disease. McCarthy (2020) identified substantially elevated cerebrovascular and Alzheimer's risk at the population level following the perimenopausal inflammatory shift — a meaningful finding, and one that is best understood as a description of group trends rather than a forecast for any individual.

Blood markers make this concrete. High-sensitivity CRP (hs-CRP) rises measurably as estradiol declines, converting what can feel like a vague cluster of mid-life complaints into a number on a blood test. This is precisely why the Regen PhD Biomarker Panel includes hs-CRP: within the framework of Regeneration by Design, inflammation occupies the centre of the Chemistry pillar — the most actionable variable to measure, track, and act on. Joint stiffness, mental fog, and a rising CRP are not unrelated inconveniences. They are the same system signalling from different addresses.

The gut loop that keeps the fire going

Buried inside the gut is a community of bacteria with a specific job: regulating how much oestrogen circulates in the bloodstream. Collectively called the estrobolome, these microbes produce an enzyme — β-glucuronidase — that frees oestrogen bound for excretion, allowing it to be reabsorbed into circulation. When the estrobolome is diverse and active, this recycling mechanism keeps circulating oestrogen topped up. When it is not, more oestrogen leaves the body unused.

Here is where the loop tightens. Declining oestrogen — for any reason — reduces microbial diversity in the gut. Lower diversity means less β-glucuronidase activity, which means less oestrogen reabsorption, which means lower circulating oestrogen still. Each step feeds the next. Peters (2022) and Wang (2025, Frontiers in Endocrinology) both document this shift: the menopausal gut becomes less diverse and begins to resemble the male gut microbiome, a pattern that may deepen the hormonal deficit rather than merely reflect it.

What makes this practically interesting is that the gut is a system with levers. Dietary diversity — a wide range of plants, fibres, and fermented foods — can support microbial richness; prebiotic and probiotic approaches may help sustain the estrobolome, though research in this area is still developing and these strategies are supportive rather than corrective. The implication, even so, is that what sits on the plate connects directly to how hormones behave — which means gut care belongs in the same conversation as hormonal health, not as a separate chapter.

Inflammaging: perimenopause inside the bigger picture

The science across the preceding sections describes something more than a hormonal fluctuation. Taken together — a molecular brake released, macrophages shifted, the gut's microbial balance disturbed — it maps what researchers now call inflammaging: the chronic, low-grade, sterile inflammation that accumulates with biological age even without infection or injury. The concept holds that this background inflammatory state is not merely a consequence of getting older; evidence increasingly suggests it may be one of its drivers.

Perimenopause does not initiate inflammaging, but it accelerates it. The hormonal transition typically arrives between ages 45 and 55 — the same decade when inflammaging begins to compound. Oestrogen's regulatory grip on NF-κB, macrophages, and the gut's microbial community had been acting as a buffer; its removal means many women enter the second half of life carrying a heavier inflammatory load than they might otherwise have done. This helps explain why cardiovascular, cognitive, and metabolic risks all shift measurably in the post-menopausal years — a period that, on average, spans roughly three decades.

This makes the midlife decade not merely a transition to endure but a biological window with consequences that extend far beyond it. That framing — that ageing is active, compounding, and to a meaningful degree designable — is central to Professor Paul Lee's Regeneration by Design (2024). Lee, an orthopaedic surgeon and biomedical engineer with an Honorary Professorship at the University of Lincoln, organises the available leverage points into four interdependent pillars: Physics, Chemistry, Biology, and Time. The perimenopause-inflammation story sits most directly in Chemistry and Biology, while the question of early intervention belongs to Time — the recognition that acting within the window of hormonal responsiveness carries more weight than acting after it has narrowed. His 2026 follow-up, Practical Regeneration, extends this into practice: gut diversity, monitored biomarkers, and small systemic adjustments treated as long-term architecture rather than short-term fixes.

What this means for you right now

Measuring inflammation turns it from background noise into a variable you can act on. High-sensitivity CRP (hs-CRP) reflects systemic inflammatory activity and is one of the most accessible places to start — it is included in the Regen PhD Biomarker Panel specifically because it registers shifts that standard NHS panels routinely overlook.

Three lifestyle inputs consistently intersect with inflammatory load during this transition: dietary diversity (particularly the range of plant-based foods that supports the estrobolome covered above), load-bearing movement to maintain joint and bone integrity, and sleep quality, which governs the overnight repair window. None of these is new advice in isolation. What the preceding sections add is mechanism — each addresses a specific node in the inflammatory system rather than a vague ideal of 'living well,' which gives food, exercise, and sleep choices a rationale that goes beyond habit.

On hormones: if HRT is something you are considering, the timing evidence is still developing and that conversation belongs with your GP or a specialist who knows your full picture. This article provides the context; the clinical decision is theirs and yours together.

The science here closes on a specific note: the inflammation measurable in your bloodwork at 45 may be more predictive of cardiovascular and cognitive health at 65 than almost any other variable you can currently assess. That is where the leverage sits — and why looking now, rather than later, matters.

This article is for general wellness information only. For any medical concern, please consult a qualified healthcare professional.

1. [1] Menopause – Wikipedia. https://en.wikipedia.org/?curid=49611 https://en.wikipedia.org/?curid=49611
2. [2] Inflammaging – Wikipedia. https://en.wikipedia.org/?curid=59830296 https://en.wikipedia.org/?curid=59830296