What age does perimenopause start in the UK?

The average UK woman starts in her mid-40s. Symptoms can appear in the late 30s or early 40s. Roughly 1 percent of women experience premature ovarian insufficiency before age 40, which needs specialist input.

How is perimenopause diagnosed?

NICE recommends symptom assessment in women over 45 rather than blood tests. Hormone levels fluctuate too widely day-to-day to be reliable. Women under 45 with menopausal symptoms are usually offered FSH and other tests to rule out other causes.

Why do gut symptoms change in perimenopause?

Oestrogen receptors are present throughout the gut. Declining and fluctuating oestrogen levels are thought to affect gut motility and barrier function, though evidence on the microbiome is mixed. Many women report new bloating, constipation or food sensitivities starting in their 40s.

For most women without contraindications, current UK guidance considers HRT safe and recommended for moderate-to-severe symptoms. The benefit-risk profile depends on age at start, route of administration (oral vs transdermal), and personal medical history. NICE updated its guidance in 2024 with a shared decision-making discussion aid and CBT as an option.

Hormones and the cycle

Perimenopause

Also called: menopause transition, climacteric

Perimenopause is the transition phase before menopause, when ovarian hormone levels start to fluctuate and decline. It typically begins in the mid-40s and lasts on average about 4 years, though it can range from 2 to 8 years. Menopause itself is the day a woman has gone 12 months without a period. Symptoms include hot flushes, sleep changes, mood shifts and, often under-discussed, gut changes.

When it starts and how long it lasts

The average UK woman starts perimenopause around age 45 and reaches menopause at 51. Some start earlier, in the late 30s or early 40s. The transition lasts on average around 4 years but commonly ranges from 2 to 8 years. Early menopause (before 45) and premature ovarian insufficiency (before 40) are clinically distinct and need specialist input.

What is happening hormonally

Oestrogen and progesterone do not decline smoothly. They fluctuate erratically before settling at the lower post-menopausal levels. The fluctuations are what cause many of the symptoms, not the absolute levels themselves. FSH (follicle-stimulating hormone) rises as the ovaries become less responsive. Blood tests are not reliable for diagnosing perimenopause because levels change day to day, which is why NICE guidance prioritises symptom assessment over blood tests in women over 45.

The classic symptoms

Period changes. Cycles become longer, shorter, heavier or lighter, often unpredictable.
Hot flushes and night sweats.
Sleep disturbance, particularly waking at 3 to 4 am.
Mood changes, anxiety, lower stress tolerance.
Brain fog and memory lapses.
Joint aches, particularly knees, shoulders, fingers.
Vaginal dryness and changes in libido.

The gut changes that often get missed

Oestrogen interacts with gut motility, the gut microbiome, and the gut barrier. As oestrogen drops, gut transit can slow (more constipation), and bloating is commonly reported. Research from King's College London on the ZOE PREDICT cohort (Bermingham et al, eBioMedicine 2022) linked menopause to changes in postprandial metabolism; in that study gut microbiome richness and diversity did not differ significantly between groups, and species-level differences did not survive correction in the age-matched analysis. Women in perimenopause report new or worsening gut symptoms more often than chance suggests.

What helps

Hormone replacement therapy (HRT). NICE recommends it as first-line for moderate-to-severe symptoms in most women without contraindications. Guidance was updated in 2024 with a shared decision-making discussion aid and a new role for CBT.
Cognitive behavioural therapy. Evidence for reducing problematic hot flushes and night sweats.
Strength training. Protects bone density and lean mass during oestrogen decline.
Adequate calcium, vitamin D, and protein intake.
Sleep prioritisation, including limiting alcohol within four hours of bed.
Diverse plant-based fibre to support the changing microbiome.

What is not perimenopause

Some symptoms attributed to perimenopause have other causes. Persistent fatigue can be iron-deficiency anaemia or thyroid disease, both more common in this age group. Sudden severe night sweats can signal infection or other conditions. Persistent heavy bleeding warrants a GP visit. It is worth ruling out the obvious before assuming everything is perimenopausal.

Common questions

What age does perimenopause start in the UK?: The average UK woman starts in her mid-40s. Symptoms can appear in the late 30s or early 40s. Roughly 1 percent of women experience premature ovarian insufficiency before age 40, which needs specialist input.
How is perimenopause diagnosed?: NICE recommends symptom assessment in women over 45 rather than blood tests. Hormone levels fluctuate too widely day-to-day to be reliable. Women under 45 with menopausal symptoms are usually offered FSH and other tests to rule out other causes.
Why do gut symptoms change in perimenopause?: Oestrogen receptors are present throughout the gut. Declining and fluctuating oestrogen levels are thought to affect gut motility and barrier function, though evidence on the microbiome is mixed. Many women report new bloating, constipation or food sensitivities starting in their 40s.
Is HRT safe?: For most women without contraindications, current UK guidance considers HRT safe and recommended for moderate-to-severe symptoms. The benefit-risk profile depends on age at start, route of administration (oral vs transdermal), and personal medical history. NICE updated its guidance in 2024 with a shared decision-making discussion aid and CBT as an option.