Esterone (E1) is one of the three major estrogens naturally produced in the human body. This steroid hormone plays a significant role in reproductive health and various bodily functions. While often considered a weaker form compared to Estradiol, Esterone serves as an important hormonal reservoir. Its influence becomes pronounced later in life, establishing it as the primary circulating estrogen following menopause.
Esterone’s Place Among Estrogens
The body produces three main forms of estrogen: Estradiol (E2), Esterone (E1), and Estriol (E3). Estradiol (E2) is the most potent and is the dominant form present in premenopausal women during their reproductive years, responsible for the most pronounced estrogenic effects in tissues like the uterus and breasts.
Esterone (E1) possesses a significantly lower biological potency, exhibiting only about 4% to 20% of the activity of Estradiol at the receptor level. This means E1 is less effective at stimulating estrogen-sensitive tissues. However, after the ovaries cease function during the menopausal transition, Esterone takes over as the most abundant estrogen circulating in the bloodstream. Estriol (E3) is primarily produced during pregnancy.
Production and Sources of Esterone
Esterone’s primary source of production shifts dramatically after a woman’s reproductive years conclude. While the ovaries produce large amounts of Estradiol during fertile years, Esterone production following menopause relies heavily on peripheral conversion.
This process involves converting precursor hormones called androgens into estrogen. The adrenal glands secrete the androgen androstenedione, which travels through the bloodstream to various tissues. The conversion is catalyzed by the enzyme aromatase, active in non-ovarian sites including muscle, liver, and fat tissue.
Adipose tissue, or body fat, is the most significant site for this extraglandular synthesis. The aromatase enzyme within fat cells transforms androstenedione into Esterone, making the amount of adipose tissue a direct determinant of circulating E1 levels. Increased body weight and fat tissue lead to higher Esterone synthesis, influencing post-menopausal hormonal status. Esterone can also be converted reversibly into the more potent Estradiol by another enzyme, allowing E1 to act as a readily available reservoir for active estrogen.
Esterone’s Primary Biological Functions
Although Esterone is less potent than Estradiol, circulating E1 levels after menopause are sufficient to maintain many physiological processes. A primary function is preserving skeletal integrity, where Esterone helps slow the accelerated bone loss associated with estrogen deficiency. It supports the balance between bone breakdown and formation.
Esterone also contributes to metabolic regulation and cardiovascular health, even as Estradiol levels decline. It influences lipid profiles, affecting cholesterol levels, and plays a role in glucose homeostasis to regulate blood sugar. While Estradiol has more pronounced effects on the cardiovascular system, Esterone provides hormonal support to the vascular system.
Furthermore, Esterone helps maintain the health and function of non-reproductive tissues, including the skin and mucosal linings. Low estrogen levels can cause symptoms like vaginal dryness and thinning skin. The weaker estrogenic activity of E1 still provides necessary stimulation to these tissues, particularly when E2 is scarce.
When Esterone Levels Are Too High or Too Low
When Esterone levels fall below a healthy range, especially in postmenopausal women, the body exhibits signs of estrogen deficiency. Insufficient E1 levels are associated with classic menopausal symptoms, such as hot flashes, night sweats, and mood changes. A sustained lack of estrogen also accelerates the loss of bone mineral density, increasing the risk of fractures.
Conversely, elevated Esterone levels can also have clinical consequences. Since adipose tissue is the main source of E1 post-menopause, conditions involving increased body fat, such as obesity, often result in higher circulating E1 concentrations. This excess E1 can overstimulate hormone-sensitive tissues, leading to an increased risk for certain cancers, most notably endometrial and breast cancer. Both excessively low and excessively high Esterone levels warrant attention for overall health management.