Oestrogen explained

The job description

Oestrogen has effects throughout the body, not just in the reproductive organs. The wide range of effects explains why hormone changes feel so significant.

In the reproductive system

Oestrogen drives the development of female sexual characteristics during puberty. It maintains the menstrual cycle through reproductive years by thickening the uterine lining, stimulating ovulation alongside other hormones and producing the cyclical changes the body goes through each month. Without oestrogen, the reproductive system would not function.

In bones

Oestrogen helps maintain bone density by influencing bone formation and breakdown. While oestrogen is present in healthy amounts, bone density stays relatively stable. When oestrogen levels fall at menopause, bone breakdown outpaces formation, which is why women lose significant bone density in the first 5 to 7 years after menopause. This is one of the most important systemic effects of oestrogen.

In the brain

Oestrogen affects neurotransmitters including serotonin, dopamine and others. It influences mood, cognition, memory and sleep. The brain has oestrogen receptors throughout. Changes in oestrogen levels produce real cognitive and emotional effects. This is why hormonal changes through the cycle, pregnancy and menopause affect mood and brain function so noticeably.

In the heart and metabolism

Oestrogen supports healthy cholesterol patterns, helps maintain blood vessel function and supports insulin sensitivity. These effects help explain why women have lower cardiovascular disease rates than men during reproductive years. This also explains why that protection fades after menopause. Oestrogen is genuinely cardioprotective during the reproductive years.

Sources and types

Oestrogen is not just one hormone. Three main forms exist in the body, each more important at different life stages.

Three main types

Oestradiol is the dominant oestrogen of reproductive years and the most potent. Oestrone is the main oestrogen after menopause and is less potent. Oestriol is produced in large amounts during pregnancy. The shift between these forms across life stages produces different effects, which is part of why the hormonal experience changes through the lifespan.

Where it is made

During reproductive years, the ovaries produce most oestrogen, particularly during the first half of each menstrual cycle. Fat tissue produces small amounts of oestrogen throughout life. The adrenal glands contribute slightly. After menopause, when the ovaries stop producing oestrogen, fat tissue becomes the main source. This is why body fat percentage affects post menopausal oestrogen levels.

The brain controls production

The hypothalamus and pituitary gland control oestrogen production by sending signals to the ovaries. FSH (follicle stimulating hormone) drives the ovaries to produce oestrogen. The brain monitors oestrogen levels and adjusts the signal as needed. This feedback loop runs the whole reproductive hormonal system.

External sources

Some plants contain compounds called phytoestrogens that have weak oestrogen like effects in the body. Soya is the most studied source. The effects of phytoestrogens are much smaller than the body's own oestrogen but may be relevant in some situations. Synthetic oestrogens in the contraceptive pill and HRT replace or supplement the body's production.

How oestrogen changes

Oestrogen levels follow predictable patterns through the female lifespan. Each phase has its own characteristic level and pattern.

Before puberty

Pre pubertal girls have low oestrogen levels. The hormonal system is essentially dormant. Puberty begins when the brain decides it is time, signalling the ovaries to start producing oestrogen. The gradual rise in oestrogen over years drives all the visible changes of puberty.

Reproductive years

Oestrogen fluctuates predictably through each menstrual cycle. It rises through the follicular phase, peaks just before ovulation, drops slightly, then has a smaller second peak in the luteal phase before falling again before the next period. Over the reproductive years, the pattern is broadly stable, though absolute levels vary between women.

Pregnancy

Oestrogen levels rise enormously during pregnancy, reaching levels far higher than anything in a normal cycle. The placenta produces large amounts. These high levels support the developing pregnancy. The dramatic drop after birth contributes to baby blues and other postpartum changes.

Perimenopause and beyond

During perimenopause, oestrogen does not just decline smoothly. It swings wildly, with both high and low cycles, producing the unpredictable symptoms of the transition. After menopause, oestrogen settles at a low level, with small amounts produced from fat tissue and other sources. This low level continues for the rest of life.

Too much, too little and treatment

Oestrogen levels can be too high, too low or out of balance with other hormones. Each pattern produces different effects.

When levels are too low

Low oestrogen produces the symptoms most associated with menopause: hot flushes, vaginal dryness, mood changes, brain fog, sleep disruption, joint aches and accelerating bone loss. Low oestrogen can also occur in women with very low body weight, severe stress, hypothalamic amenorrhoea or premature ovarian insufficiency. Treatment depends on the cause but often involves addressing the underlying issue or hormone replacement.

When levels are too high

Excess oestrogen relative to progesterone, sometimes called oestrogen dominance, contributes to heavy periods, breast tenderness, mood symptoms, fibroids and increased risk of certain cancers. This pattern often occurs in perimenopause when progesterone falls earlier than oestrogen. Treatment may involve managing the underlying cause or adding progesterone.

HRT and treatment

Hormone replacement therapy adds oestrogen back to address menopausal symptoms. Modern HRT typically uses body identical oestrogen delivered through the skin via patches, gels or sprays. This route avoids the blood clot risk associated with oral oestrogen. The dose can be adjusted to match individual needs. Speak to your GP about whether HRT is appropriate for you.

Testing levels

Blood tests can measure oestrogen levels, though the fluctuations through the cycle and across life stages make single measurements less useful than people sometimes expect. Levels are most useful in specific clinical situations rather than as routine checks. Speak to your GP about whether oestrogen testing would add useful information for your situation.

More on female health

For the balancing hormone, our Progesterone: What It Does and Why It Matters covers the partner to oestrogen. What Low Oestrogen Does to the Body covers the effects of low levels. And Menopause: A Complete Guide covers the life stage where oestrogen changes most dramatically.