1 / What Is Actually Happening to Your Hormones After 45?

If your periods, sleep, mood, energy or even the way you respond to stress suddenly seem different, there is a biological reason. Perimenopause is not simply a slow decline in estrogen. It is a period of changing and often unpredictable communication between your brain and ovaries.

Understanding that changes the whole menopause conversation.

The main hormones involved

Several hormones are involved in the menopause transition, but four are particularly useful to understand.

Estradiol is the main form of estrogen during the reproductive years. It influences far more than your menstrual cycle, including your brain, bones, cardiovascular system, vaginal and urinary tissues, body composition and temperature regulation.

Progesterone rises after ovulation and helps regulate the menstrual cycle. As ovulation becomes less reliable during perimenopause, progesterone production becomes less consistent too.

FSH, or follicle stimulating hormone, is produced by the pituitary gland in your brain and tells the ovaries to develop follicles and produce estrogen. As the ovaries become less responsive with age, the brain generally produces more FSH in an attempt to stimulate them.

LH, or luteinising hormone, is another pituitary hormone involved in ovulation and ovarian function. Its patterns also change as ovarian function declines.

These hormones don't operate independently. They are part of a communication network between your brain and ovaries called the hypothalamic pituitary ovarian axis.

And during perimenopause, that communication becomes increasingly unpredictable.

It starts with your ovaries, but your brain is involved too

Women are born with a finite number of ovarian follicles. Over the reproductive years, their number and quality gradually decline.

Eventually the ovaries stop responding to signals from the brain as consistently as they once did. The brain responds by increasing its signalling, particularly FSH, in an attempt to encourage the ovaries to produce estrogen and develop a follicle.

Sometimes the ovaries respond. Sometimes they don't. Ovulation becomes less predictable, and the familiar hormonal rhythm of the menstrual cycle begins to change.

This is the biological transition we call perimenopause.

It usually begins years before the final menstrual period, which is why you can experience significant symptoms while still having periods.

Estrogen doesn't simply decline

This is probably the single most important thing to understand about perimenopause.

Estrogen does not usually descend in a neat, predictable line.

During perimenopause, estradiol can fluctuate considerably. At times it may be relatively low. At other times it can rise quite high. Eventually, after menopause, ovarian estradiol production settles at consistently lower levels.

That helps explain why perimenopause can feel so erratic.

You may have several perfectly reasonable months followed by a month when your breasts hurt, your period is unusually heavy, you cannot sleep and everyone in your immediate vicinity suddenly seems extraordinarily annoying.

Then you feel better again.

The hormonal environment is changing, but it isn't changing at exactly the same rate every day or every month.

This is also one reason a single estrogen blood test during perimenopause often tells us very little. It captures one moment in a highly variable transition.

Progesterone can change earlier than you expect

Progesterone adds another piece to the puzzle.

Progesterone rises after ovulation. But as ovarian ageing progresses, ovulation can become less frequent and less predictable.

If you don't ovulate, you don't produce the usual post ovulation rise in progesterone.

This means that during perimenopause, progesterone exposure can become inconsistent while estrogen is still being produced and fluctuating considerably.

The changing relationship between estrogen and progesterone can contribute to shorter or longer cycles, skipped periods and changes in menstrual flow.

This is also why I prefer to be careful with the popular term estrogen dominance. It is often used online as though it were a clearly defined diagnosis responsible for everything from breast tenderness to belly fat.

The actual physiology is more useful. During perimenopause, ovulation becomes less reliable, progesterone exposure can decline or become inconsistent and estrogen can fluctuate widely.

You don't need a catchy hormone label to explain what is happening.

Why can this affect so much more than your periods?

Estrogen receptors exist throughout the body, so changes in estrogen signalling are not limited to the reproductive system.

The brain is one important example. Changing estrogen signalling can influence systems involved in temperature regulation, sleep, mood and cognitive function. This helps explain why hot flushes, night sweats, disrupted sleep, mood changes and brain fog can appear during the menopause transition.

Estrogen also plays an important role in maintaining bone. As estrogen levels remain lower after menopause, bone breakdown accelerates, contributing to increasing osteoporosis risk.

Changes also occur in body composition and fat distribution. As we discussed in the Weight and Metabolism series, menopause tends to favour greater central and visceral fat accumulation, while ageing and menopause can contribute to declining lean mass.

The vaginal and urinary tissues are estrogen sensitive too. Declining estrogen can contribute to vaginal dryness, discomfort during sex, urinary symptoms and recurrent urinary tract infections, collectively known as genitourinary syndrome of menopause.

This is why menopause is much bigger than periods stopping. It is a whole body transition.

Why do symptoms come and go?

This is one of the most confusing aspects of perimenopause.

You can feel dreadful for three months and then suddenly feel almost normal. Your periods can become irregular and then apparently settle again. Hot flushes can appear, disappear and return.

That doesn't necessarily mean you've somehow reversed perimenopause.

Hormone production during this stage can be highly variable, and symptoms don't always move in a straight line either.

The transition itself also changes over time. Earlier in perimenopause, relatively subtle changes in cycle length may be the first clue. Later, longer gaps between periods become more common.

Eventually menstruation stops. Menopause itself is confirmed retrospectively after 12 consecutive months without a menstrual period, assuming there is no other cause.

The average age of natural menopause is around 51, but there is considerable individual variation.

Hormones can affect mood, sleep and your brain

Many women tell me that the psychological changes surprise them more than the physical ones.

You may suddenly feel more anxious, irritable or emotionally sensitive. Concentration can become harder. Words disappear halfway through sentences. Sleep becomes unreliable.

Estradiol interacts with neurotransmitter and neural systems involved in mood, cognition, sleep and stress response, so hormonal fluctuations can contribute to these changes.

But this is an important place to avoid blaming everything on menopause.

Sleep problems can also result from sleep apnoea, stress, alcohol, medication and other health conditions. Fatigue can have dozens of causes. Anxiety and depression deserve proper assessment. Significant or progressive cognitive changes should never simply be dismissed as menopause brain fog.

Menopause can be part of the explanation without necessarily being the whole explanation.

What happens after menopause?

Once the ovaries stop releasing eggs and menstrual cycles end, the dramatic hormonal fluctuations of perimenopause generally settle. Ovarian production of estradiol and progesterone remains much lower, while FSH and LH remain higher.

That doesn't mean every symptom immediately disappears.

Hot flushes can continue for years in some women. Sleep may remain affected. Vaginal and urinary symptoms can develop or progress after menopause. Lower estrogen also becomes increasingly relevant to bone health, body composition and the broader cardiovascular and metabolic picture.

So menopause isn't simply something you "get through" until the periods stop. It changes the health priorities we need to think about in the decades that follow.

Not everything after 40 is hormonal

This is just as important as understanding what hormones can do.

Fatigue, weight gain, hair loss, palpitations, poor sleep, anxiety, heavy bleeding and brain fog can occur during perimenopause. They can also occur with thyroid disease, iron deficiency, diabetes, sleep disorders, medication effects and many other conditions.

Heavy or unusual bleeding in particular should not automatically be dismissed as perimenopause.

Good menopause care means recognising symptoms that fit the transition while remaining curious when something doesn't.

You don't need to balance your hormones

I would love to remove this phrase from the menopause vocabulary.

Your reproductive hormones are supposed to change during this stage of life. No diet, supplement or detox can make your ovaries behave as though you are 35 again.

And that isn't our goal.

Our goal is to help your body adapt to the transition, reduce symptoms that are affecting your quality of life and protect your long term health.

Sometimes lifestyle changes can make an enormous difference. Sometimes menopausal hormone therapy or another medical treatment is appropriate. Often we use a combination of approaches.

But first, you need to know what you are trying to change.

Which biomarkers I recommend checking

For most otherwise healthy women over 45 with typical perimenopausal symptoms and menstrual changes, routine reproductive hormone testing is often unnecessary. FSH and estradiol can fluctuate substantially, so one blood test may tell us very little about where you are in the transition.

Testing becomes more useful when symptoms are unusual, menopause is suspected at a younger age or another health condition may be contributing.

Depending on your symptoms and history, this might include TSH and free T4 for thyroid function, full blood count and ferritin where heavy bleeding or iron deficiency is possible, and fasting glucose, HbA1c and a lipid profile as part of broader midlife health assessment.

We will look specifically at FSH, estradiol, progesterone, testosterone, thyroid markers and popular hormone testing in the final article in this series.

Your next step

Now we have the important part clear. Perimenopause is not simply estrogen disappearing. Ovulation becomes less predictable, progesterone exposure changes, estradiol fluctuates and communication between the brain and ovaries gradually shifts until the reproductive years come to an end.

The next question is much more practical: what can you actually do to make this transition easier on your body?

Next: Where to Start When Your Hormones Feel All Over the Place

You can also explore more articles, free and paid resources, my book and programmes in the Hormones and Menopause section of Feel Good Menopause.