Aromatization
Definition
Aromatization is the enzymatic conversion of androgens (testosterone and androstenedione) into estrogens (estradiol and estrone), carried out by the aromatase enzyme. After menopause, this peripheral conversion — primarily in adipose tissue — becomes the body's main source of estrogen.
In Depth
Before menopause, the ovaries are the dominant source of estradiol. After menopause, when ovarian estrogen production has effectively ceased, the body's circulating estrogen comes largely from a different route: aromatization. The adrenal glands continue producing androgens (chiefly androstenedione and DHEA), and the aromatase enzyme — present in fat, muscle, skin, bone, and brain — converts a fraction of these androgens into estrone and a smaller amount of estradiol.
This explains several clinical observations. Postmenopausal women with more adipose tissue typically have higher circulating estrone levels, because adipose tissue is a major aromatization site. This is one reason obesity is associated with both reduced vasomotor symptoms in some women and increased risk of estrogen-sensitive cancers (notably endometrial cancer and postmenopausal breast cancer). It also explains the mechanism of aromatase inhibitors (anastrozole, letrozole, exemestane), which are used in postmenopausal estrogen receptor-positive breast cancer to block this peripheral estrogen production and starve estrogen-driven tumors.
Aromatization is bidirectional in clinical importance: it provides the modest residual estrogen that protects bone and tissue in some postmenopausal women, but it can also fuel hormone-sensitive disease, which is why targeting the enzyme has become a cornerstone of breast cancer therapy.
Why It Matters
Aromatization is the reason "no ovaries" does not mean "no estrogen." Understanding it clarifies why body composition affects symptom severity, why aromatase inhibitors cause menopause-like side effects, and why postmenopausal estrogen is rarely truly zero.