E2; estradiol; 17-beta (o)estradiol
Oestradiol is a steroid hormone made from cholesterol and is the strongest of the three naturally produced oestrogens. It is the main oestrogen found in women and has many functions, although it mainly acts to mature and maintain the female reproductive system. A natural boost in oestradiol levels during the menstrual cycle causes an egg to mature and be released, as well as thickening the uterus lining so that the egg can implant if it becomes fertilised. Oestradiol also promotes development of breast tissue and increases bone and cartilage thickness.
In premenopausal women, oestradiol is mostly made by the ovaries. Oestradiol levels vary throughout the monthly menstrual cycle, being highest at ovulation and lowest at menstruation. Oestradiol levels in women reduce slowly with age, with a large decrease occurring at the menopause when the ovaries switch off.
Men also produce oestradiol. It is made in the same pathway as testosterone. However, levels are much lower than in women. In both sexes, oestradiol is also made in much smaller amounts by fat tissue, the brain and the walls of blood vessels.
Production of oestradiol in women’s ovaries involves a chain reaction of hormones known as the hypothalamic-pituitary-gonadal axis. This begins with the hypothalamus in the base of the brain, which releases a hormone called gonadotropin-releasing hormone. In turn, this makes the pituitary gland release two further hormones, luteinising hormone and follicle stimulating hormone. They enter the blood and stimulate the ovary and immature follicles containing an egg. These begin to produce oestradiol. Communication between oestradiol levels in the circulation and the brain controls development of an egg, ovulation and the menstrual cycle.
Too much oestradiol can have a number of effects. In mild cases, excess levels cause acne, constipation, loss of libido and depression. More severe effects can include uterine and breast cancer, female infertility, weight gain, stroke and heart attack.
In men, too much oestradiol can also cause sexual dysfunction, loss of muscle tone, increased body fat and development of female characteristics, such as breast tissue. Oestradiol becomes more dominant as a man ages and his testosterone production reduces, which scientists think may be a contributing factor in the development of prostate cancer.
Oestradiol is used in hormone replacement therapy to relieve symptoms of the menopause in women. There are many recognised pros and cons to hormone replacement therapy. See the article on menopause for more information.
Oestradiol is necessary for bone development, so people with low oestradiol tend to have skeletal problems like inadequate bone growth and osteoporosis. Girls will also encounter problems at puberty such as a delay in, or failure of, breast development, a disrupted or absent menstrual cycle and infertility. Oestradiol also has important roles in the brain, where low levels can cause depression, fatigue and mood swings.
A woman’s oestradiol production falls naturally at the menopause and causes many of its symptoms. Initially these include night sweats, hot flushes, vaginal dryness and mood swings, whilst in the long term she is more likely to develop osteoporosis.
Last reviewed: Jan 2015