Synthesised from cholesterol, this steroid hormone is produced in the ovaries of premenopausal women, where it acts as a powerful reproductive hormone and is highest during ovulation and lowest during menstruation. As the main hormone of the three naturally produced oestrogens, it is also produced in the testes of men, but in smaller amounts. In both sexes, oestradiol is made in significantly reduced amounts by the brain, fat tissue, and in the walls of the blood vessels.

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