What happens to your body during perimenopause: a system-by-system guide

At what age does perimenopause typically begin?

NICE guidance notes that perimenopause most commonly begins in a woman's mid-to-late 40s, but can start earlier. The NHS defines the average age of menopause in the UK as 51. The perimenopausal transition typically lasts four to eight years, though this varies considerably between individuals.

Why do lipid profiles change during perimenopause?

Oestradiol upregulates hepatic LDL receptor expression and promotes hepatic HDL synthesis. As oestradiol declines, LDL clearance from circulation decreases, HDL production can fall, and hepatic triglyceride output increases. This is a direct metabolic consequence of reduced E2 signalling on hepatic sterol regulation, documented in population studies of women crossing the menopausal transition.

Why does bone mineral density decrease during perimenopause?

Oestradiol maintains the RANKL/OPG balance in bone towards suppression of osteoclast activity. As E2 declines, the RANKL/OPG ratio shifts towards osteoclastogenesis — more osteoclast differentiation, more bone resorption — while osteoblast activity and bone formation decrease. The net result is a measurable reduction in BMD, accelerating during the late perimenopausal and early postmenopausal years.

Is perimenopause a medical condition?

No. Perimenopause is a natural life stage — the biological transition preceding menopause. It is not a disorder or a condition requiring treatment in itself, though the physiological changes it involves are significant and well-characterised. NICE guidance on menopause (NG23) describes it as a stage of life that warrants appropriate clinical support and information.

What happens to oestrogen receptors in the brain during perimenopause?

A 2024 PET imaging study (Weill Cornell Medicine) found that ER density in multiple brain regions increases progressively during the perimenopausal and postmenopausal years, compared to premenopausal controls. The researchers interpret this as a compensatory upregulation — brain cells expressing more receptors to capture the diminishing oestradiol signal. ER density in the pituitary, caudate nucleus, posterior cingulate, and middle frontal cortex predicted menopausal status with 100% accuracy in the study cohort.