Oestrogen: what it does, and signs of low and high levels

What is oestrogen?

Oestrogen (spelt "estrogen" in American English) is not one hormone but a group of related hormones. The three main ones are:

• Oestradiol – the strongest and most important form during the reproductive years, made mainly by the ovaries.
• Oestrone – the main form after menopause, made largely in fat tissue from other hormones.
• Oestriol – produced in large amounts by the placenta during pregnancy.

Men make oestrogen too, in smaller amounts, and it matters for their bones and fertility. In women, it works alongside progesterone to run the menstrual cycle.

What does oestrogen do in the body?

Oestrogen receptors are found throughout the body, which is why the hormone has such wide-ranging effects:

How do oestrogen levels change through life?

Oestrogen rises at puberty and, during the reproductive years, follows a monthly rhythm: it climbs in the first half of the cycle, peaks just before ovulation and rises again more modestly in the second half. Levels are very high in pregnancy and drop sharply after birth, staying low while breastfeeding.

In perimenopause, the rhythm breaks down and oestrogen fluctuates unpredictably, sometimes higher than before and sometimes very low. After menopause, the ovaries make very little and oestrogen settles at a permanently lower level.

What happens to oestrogen during menopause?

As the supply of eggs in the ovaries runs out, they stop producing oestradiol in any meaningful amount. The body still makes a little oestrone in fat tissue, but overall levels are much lower than before. The tissues that depended on oestrogen respond to that change, which is what causes most menopause symptoms – from hot flushes to vaginal dryness – and the faster loss of bone density that raises the risk of osteoporosis.

What are the symptoms of low oestrogen?

Low oestrogen is most common around and after menopause, but it can also happen earlier – for example with premature ovarian insufficiency, after surgery to remove the ovaries, during breastfeeding, or when periods stop because of very low body weight, intense exercise or stress. Typical symptoms include:

• irregular, light or absent periods
• hot flushes and night sweats
• vaginal dryness, soreness and pain during sex
• more frequent urinary infections or needing to pee more often
• low mood, anxiety, irritability and difficulty concentrating
• poor sleep
• dry skin and thinning hair
• reduced sex drive
• over time, thinner bones and a higher risk of fractures

What are the symptoms of high oestrogen?

Higher than usual oestrogen, or oestrogen that is not balanced by enough progesterone, can be linked with heavy or irregular periods, breast tenderness, bloating and fluid retention, and in some cases conditions such as fibroids or a thickened womb lining. It can occur in perimenopause, with obesity (fat tissue makes oestrogen), with some medicines, and – rarely – with hormone-producing tumours.

You may see the term "oestrogen dominance" online, often with long symptom lists and promises of diets or supplements to fix it. It is a popular idea, not a medical diagnosis, and the symptoms attributed to it overlap with many other conditions. If you have heavy, painful or irregular periods, bleeding between periods or after sex, or bleeding after menopause, see your GP so the cause can be properly assessed.

Can you test your oestrogen levels?

Yes, oestradiol can be measured with a blood test, but the result is often less useful than people expect. In perimenopause oestrogen swings from day to day, so a single reading can look normal, high or low depending on when it was taken. For women aged 45 and over with typical symptoms, GPs are advised not to use oestradiol or other hormone tests to diagnose perimenopause or menopause – the diagnosis is based on symptoms and periods.

Blood tests are more useful in younger women, for example to investigate missed periods or suspected premature ovarian insufficiency, usually alongside follicle-stimulating hormone (FSH). Home test kits measure the same things and have the same limitations, so it is best to interpret any result with a GP.

How is low oestrogen treated?

Treatment depends on the cause and is decided with a doctor. Around menopause, hormone replacement therapy (HRT) replaces oestrogen through tablets, patches, gels or sprays, usually combined with a progestogen if you have a womb. Vaginal oestrogen – a low-dose cream, pessary, gel or ring – treats dryness and urinary symptoms locally and can be used alongside HRT. For women with early or premature menopause, hormone treatment is usually recommended at least until the natural age of menopause to protect bones and heart.

Lifestyle also matters for the tissues oestrogen used to protect: weight-bearing and strength exercise for bones, calcium-rich foods, vitamin D in autumn and winter, not smoking and drinking less alcohol.

What are phytoestrogens?

Phytoestrogens, or plant oestrogens, are natural compounds in some plants that have a structure similar to oestrogen and can bind weakly to oestrogen receptors. A well-known group is the isoflavones, found in soya beans and foods made from them, chickpeas and other pulses, and red clover. Lignans, another type, are found in linseed (flaxseed) and wholegrains.

Studies have looked at whether phytoestrogens affect menopausal symptoms such as hot flushes. The results are mixed: some studies show modest effects, others none, partly because people absorb and process them differently and because amounts vary widely between foods and products. There is no approved health claim for phytoestrogens, they are far weaker than the body’s own oestrogen, and they are not a replacement for it or for HRT.

Including soya, pulses and linseed as part of a varied diet is fine for most people. If you have had breast cancer or take medicines such as tamoxifen, talk to your specialist before taking concentrated phytoestrogen products.