Dehydroepiandrosterone is a precursor hormone, which means it has little biological effect on its own, but has powerful effects when converted into other hormones such as testosterone and oestradiol. Dehydroepiandrosterone is produced from cholesterol mainly by the outer layer of the adrenal glands, known as the adrenal cortex, although it is also made by the testes and ovaries in small amounts. It circulates in the blood, mainly attached to sulphur as dehydroepiandrosterone sulphate, which prevents the hormone being broken down. In women, dehydroepiandrosterone is an important source of oestrogens in the body – it provides about 75% of oestrogens before the menopause, and 100% of oestrogens in the body after menopause. Dehydroepiandrosterone production increases from around nine or ten years of age, peaks during the 20s and gradually decreases into old age. Dehydroepiandrosterone is also produced in small amounts by the brain, although its precise role there is not clear. Dehydroepiandrosterone production is controlled by the brain in a negative feedback loop. This means that when dehydroepiandrosterone levels in the body fall, the system is 'switched on' and, as levels rise, it 'switches off' again. The system is 'switched on' by corticotrophin-releasing hormone being produced by the hypothalamus. This travels to the anterior pituitary gland and causes it to release adrenocorticotropic hormone into the bloodstream. Both of these hormones cause the adrenal glands to produce dehydroepiandrosterone. When dehydroepiandrosterone levels rise, the body shuts off production by stopping corticotrophin-releasing hormone and adrenocorticotropic hormone.