What causes menopause?

At some point, every woman experiences it. Yet despite its inevitability, menopause remains poorly understood, even by those living through it. Too often, it’s reduced to hot flushes, sleepless nights, or a punchline about midlife. But menopause is a biological shift rooted in complex hormonal changes that affect nearly every organ system in the body.

Menopause is when your periods stop for 12 months in a row, marking the natural end of your ability to get pregnant and signalling that your ovaries are no longer working the way they used to. It typically occurs between the ages of 45 and 56, with the average age hovering around 51 in the UK.¹ But menopause doesn’t begin with a single skipped period. It starts years earlier, in a phase known as perimenopause, as the ovaries gradually lose their ability to function.

What menopause is and how it happens

The ovaries have a finite supply of eggs. Women are born with around one million ovarian follicles, and by puberty, that number drops to approximately 300,000. From that point on, most follicles are lost through a natural process called atresia, and fewer than 500 will ever fully mature in a woman’s lifetime and be released during ovulation.²

As the number and quality of these follicles decline, so does the production of estradiol and inhibin B, which are two hormones central to the regulation of the menstrual cycle. In response, the brain ramps up production of follicle-stimulating hormone (FSH) and luteinising hormone (LH) in an effort to stimulate ovulation. But by the time a woman reaches her late 40s or early 50s, the hormonal feedback loop that has governed her reproductive life begins to fail.³ Ovulation becomes irregular. The length of menstrual cycles change, become erratic, and eventually stop altogether.

Why the decline in hormones is significant

It’s the drop in oestrogen that drives the classic symptoms of menopause: hot flushes, mood changes, sleep disturbances, vaginal dryness, and trouble with memory. Because oestrogen receptors are found throughout the body and not just in reproductive tissues, its absence has wide-ranging consequences. Risk of fractures increases. Higher risk of stroke, heart attacks, and other heart conditions. Skin thins. Even brain function may take a hit.³

These symptoms are not evenly distributed. Studies suggest that between 75 and 80 percent of women experience vasomotor symptoms such as hot flushes and night sweats.⁴ For some, they last a few months. For others, particularly Black women, they can persist for up to a decade. Cultural, genetic, and environmental factors all play a role in how menopause is experienced and how early it begins.³

Reasons why menopause can occur early

While natural menopause is the most common pathway, some women undergo what’s known as induced or surgical menopause. This can occur following the removal of both ovaries, cancer treatments like chemotherapy or radiation, or as a result of certain medical conditions that impair ovarian function.⁵ In these cases, menopause can occur suddenly and at a younger age, often with more severe symptoms due to the abrupt loss of hormone production.

Going through menopause before the age of 40

Menopause in under 40s is classified as premature ovarian insufficiency (POI), a condition that affects roughly 1 percent of women.⁶ POI can be idiopathic (meaning no clear cause is identified) or linked to autoimmune disease, genetic abnormalities, or prior medical treatments.⁶ Regardless of the cause, the health implications are similar and often more serious due to the early and prolonged exposure to low oestrogen levels.

Why timing matters

Women who go through menopause earlier than average are at increased risk of osteoporosis, cardiovascular disease, and early death.⁷ Lifestyle factors appear to influence timing, as smokers tend to reach menopause about two years earlier than non-smokers, while women who have given birth or used hormonal contraceptives may experience menopause slightly later.⁸ 

The numan take

Menopause is not just the end of periods, but a major hormonal shift that can affect everything from your bones to your brain. Whether it happens naturally, suddenly, or earlier than expected, understanding what’s going on in your body is the first step to feeling more in control.

References

1. Website NHS. Menopause. nhs.uk. https://www.nhs.uk/conditions/menopause/ [Accessed 15th July 2025].

2. Park SU, Walsh L, Berkowitz KM. Mechanisms of ovarian aging. Reproduction. 2021;162(2): R19–R33.

3. Peacock K, Carlson K, Ketvertis KM. Menopause. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2025.

4. Thurston RC, Joffe H. Vasomotor symptoms and menopause: findings from the Study of Women’s Health across the Nation. Obstetrics and gynecology clinics of North America. 2011;38(3): 489–501.

5. Secoșan C, Balint O, Pirtea L, Grigoraș D, Bălulescu L, Ilina R. Surgically induced menopause-A practical review of literature. Medicina (Kaunas, Lithuania). 2019;55(8): 482.

6. Early and premature menopause. NHS inform. https://www.nhsinform.scot/healthy-living/womens-health/later-years-around-50-years-and-over/menopause-and-post-menopause-health/early-and-premature-menopause/ [Accessed 15th July 2025].

7. Faubion SS, Kuhle CL, Shuster LT, Rocca WA. Long-term health consequences of premature or early menopause and considerations for management. Climacteric: the journal of the International Menopause Society. 2015;18(4): 483–491.

Peycheva D, Sullivan A, Hardy R, Bryson A, Conti G, Ploubidis G. Risk factors for natural menopause before the age of 45: evidence from two British population-based birth cohort studies. BMC women’s health. 2022;22(1): 438.