Why does menopause happen?

Why does menopause happen, especially when life already feels like a whirlwind? Unravelling the mystery isn’t just about biology but understanding the complex dance of hormones and how they shape this pivotal phase in a woman’s life.

 Let’s take a few minutes to dig into the biology and understand why women experience menopause.

Two million eggs

Understanding why menopause happens begins with looking at our biological foundations, starting right from birth.

All the eggs (ova) you will ever have develop in your ovaries before birth. You are born with between one and two million eggs, but immediately, they start to die so that by the time you start having periods, that number is down to between 300,000 and 500,000. 

During each monthly cycle, an egg develops in the ovary. Specialist cells in the ovarian tissue around the egg produce the hormones estrogen and progesterone, which prepare the lining of the uterus to support a pregnancy. If the egg isn’t fertilised, the hormone profile changes, the uterus lining is shed – a period – and the cycle starts again.

In most months, only a single egg will mature and undergo ovulation, but thousands more are dying. By your early thirties, there are up to 150,000 left; by your early 40s, between five and ten thousand.

Declining egg numbers lead to menopause

The role of hormones

Let’s look briefly at the role hormones play in the reproductive cycle. It’s easy to overcomplicate things, so we’ll keep it simple.

Early in the cycle, follicle-stimulating hormone (FSH) is produced by the pituitary gland at the base of the brain. FSH causes a small number of eggs to start maturing in the ovary. The egg matures inside a structure called a follicle (hence follicle-stimulating hormone).

The developing follicle produces oestrogen. This is detected by a gland attached to the pituitary (the hypothalamus), which shuts down the production of FSH so you don’t have too many follicles developing at once.

The estrogen also causes the pituitary gland to produce another hormone called luteinising hormone (LH), which causes the egg to be released from the ovary – ovulation.

After the egg has been released, the follicle left behind starts to produce progesterone. After about ten days, the follicle (now called the corpus luteum) breaks down and stops producing progesterone. As a result, the uterus lining degenerates, and the period happens.

From this information, we can predict what will happen to these hormones around menopause. Because the eggs have almost all been used up, there are few follicles, so much less estrogen and progesterone are produced. Because there is little estrogen, there’s nothing to stop the production of FSH by the pituitary, so levels of FSH go sky high trying to stimulate follicles that aren’t there anymore.

In theory, a blood test around menopause would show a low estrogen and progesterone and a high FSH. In practice, the hormone levels tend to swing around quite a lot, making a single test not very useful.

It’s the swinging and falling hormone levels that cause the signs and symptoms of menopause

Cells all around the body are dependent on estrogen to work effectively.

Once the number of remaining eggs reaches a critical mass, there isn’t a regular supply of follicles to produce dependable estrogen levels. Although the general trajectory is downwards, day-to-day estrogen levels can swing wildly. This leaves cells within the body struggling to play catchup. The result is the menopausal symptoms that most women experience: hot flashes and night sweats, mood swings, anxiety and depression as they go through menopause.

Talk to a group of women in their 40s and 50s, and you’ll likely hear a chorus of shared experiences: the unexpected hot flash during an important meeting, the sudden mood swing before a family event. These are the hallmarks of perimenopause, a chapter many of us know all too well.

Long-term low estrogen levels lead to the symptoms and consequences of postmenopause

While the erratic dance of hormones defines perimenopause, the settled but low levels post-menopause have lasting implications.

The turmoil of symptoms caused by erratic hormone levels that in day-to-day language is called menopause is officially called perimenopause. Menopause refers not to a period of time but to a specific event: the final menstrual period. We explore the different stages of menopause in another article.

Once menopause, the last period, has occurred, there are no more developing egg follicles. Levels of estrogen and progesterone now settle to their new postmenopausal levels. Most symptoms of perimenopause gradually resolve, but new symptoms take their place, notably vaginal dryness and other genitourinary symptoms.

Since estrogen plays a vital role in maintaining the health of tissues all around the body, the low levels have consequences in the years after menopause. Think of it like driving your car when it’s short of oil. These consequences for postmenopausal women include an increased risk of osteoporosis, heart disease and dementia.

The natural ebb of estrogen has clear consequences, but what about those who experience menopause earlier or due to medical reasons?

Premature causes of menopause

While we’ve primarily discussed natural menopause to explain why menopause happens, not everyone’s journey follows this path.

Menopause may also occur early, unexpectedly or abruptly. Early menopause occurs before age 45, whilst premature menopause (or premature ovarian insufficiency) occurs before 40. Many factors can lead to menopause occurring earlier than expected, including genetics and autoimmune conditions. We’ll look at these factors in another article.

Jasmine had done her reading. Diagnosed with a genetic mutation that put her at high risk for ovarian cancer, she chose to have her ovaries removed. She had stocked up on fans, breathable bedding, and even joked with her husband of the potential mood swings. Yet, no amount of reading prepared her for the emotional whirlwind of stepping into menopause overnight.

Menopause can also be induced as a result of medical treatment. Commonly, this is a result of treatment for cancers affecting the ovaries, which may be removed with or without the uterus (hysterectomy). The ovaries can also be removed or damaged during surgical treatment of the uterus or cervix. The ovaries may also be removed for other conditions, such as polycystic ovarian syndrome (PCOS) or endometriosis. Menopause occurring in this way is called surgical menopause.

Another common medically-induced cause of menopause occurs when chemotherapy or hormone-blocking treatment is given for cancer. Often, though not always, this is for breast cancer.

Whatever the cause, the underlying reason for menopause is when the ovaries stop producing estrogen. It’s because of this that women may experience menopause symptoms.

Knowledge is power

Just as you asked, ‘Why does menopause happen?” with every stage of menopause, understanding its root causes can be empowering. We’re here to make that knowledge accessible with our research-driven articles. And for those seeking a comprehensive guide, ‘The Menopause Handbook‘ is a dependable ally. If you still have questions, leave a comment or send us a message.