Understanding Estrone: The Role and Impact of the E1 Hormone

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer

Estrone (E1) is a naturally occurring female sex hormone and the weakest of the three main types of estrogen [4]. It is produced mainly in the adrenal glands, body fat and ovaries [4] and supports bone strength and blood vessel health [4]. After menopause, it is the body's primary natural estrogen source [4], and obesity can cause overproduction that may raise certain cancer risks [3] [4].

What the research says

• Higher blood levels of estrone and other sex hormones go with higher breast cancer risk after menopause. In a reanalysis of nine prospective studies (663 women who developed breast cancer and 1,765 who did not, none using hormone medicines when blood was drawn), risk rose significantly with increasing concentrations of all the sex hormones examined, including estrone and estradiol. For example, the highest estradiol quintile carried a relative risk of 2.00 (95% CI 1.47–2.71) versus the lowest (PubMed: Key et al., J Natl Cancer Inst, 2002 [1]).

• Body weight and estrone move together. In a pooled analysis of 18 prospective studies of postmenopausal women, estradiol and estrone were strongly and positively associated with body mass index regardless of the lab method used, and all three hormones studied were strongly associated with breast cancer risk. Measured hormone concentrations were highest with direct immunoassays and lowest with mass spectrometry, so numbers differ by method (PubMed: Key et al., Steroids, 2014 [2]).

• Fat tissue is an active estrogen factory. A 2024 review of obesity-associated breast cancer reports that increased estrogen levels, driven by excessive aromatization activity in adipose tissue, contribute to breast cancer development in obese women, alongside insulin resistance, inflammation, and other factors (PubMed: Engin, Adv Exp Med Biol, 2024 [3]).

The Function of Estrone

Estrone, often referred to as E1, is a foundational hormone that supports various bodily systems beyond reproductive health.

Key biological roles

Although it is less powerful than estradiol [4], estrone remains a vital component of hormonal health:

• Hormonal conversion. The body can convert estrone into estradiol when a stronger form of estrogen is required for reproductive processes [4].

• Bone and brain health. Estrone helps maintain bone density and supports cognitive (thinking) functions [4].

• Vascular support. It aids in the production of nitric oxide, which helps blood vessels remain open and functional [4].

Postmenopausal significance

After menopause, when the ovaries stop producing significant amounts of other estrogens, estrone becomes the primary natural estrogen in the female body [4]. It is synthesized from precursors in the adrenal glands and body fat [4].

Phase / group	Normal range (pg/mL)
Males	15 – 65 [4]
Females (follicular phase)	100 – 250 [4]
Females (luteal phase)	15 – 200 [4]
Females (postmenopause)	15 – 55 [4]

Reference ranges can differ between laboratories and test methods [2] [4], so compare your result with the range printed on your own lab report.

Production and Anatomy

Estrone is produced in several areas of the body, depending on sex and life stage.

• Adrenal glands. These small glands located above the kidneys produce estrone in all sexes [4].

• Adipose tissue. Body fat is a major site of estrone synthesis [4], which is why body weight can significantly impact hormone levels [2].

• Ovaries. In females before menopause, the ovaries are a key production site [4].

Figure 1: Estrone is synthesized in fat tissue and the adrenal glands, and can be converted into stronger estradiol.

Conditions Related to Estrone Levels

Maintaining balanced estrone levels is crucial for long-term health, as both high and low levels are linked to specific medical concerns.

Risks of low estrone

Low levels of estrogen, including estrone, are a primary driver of postmenopausal health issues:

• Osteoporosis. Reduced estrone increases the risk of bone thinning and fractures [4].

• Menopausal symptoms. Low levels can contribute to persistent fatigue, hot flashes, and a reduced sex drive [4].

Risks of high estrone

Excessive estrone production is often linked to lifestyle factors and can have serious implications:

• Obesity. Because estrone is produced in fat cells, higher body fat percentages often lead to elevated E1 levels [2] [4] (see our obesity guide).

• Cancer risk. High estrone levels have been associated with increased tumor growth in breast and endometrial cancers [4] (see estrogen-dependent cancers and ER-positive breast cancer).

Estrone level	Possible concerns
Low	Osteoporosis (bone thinning and fractures) [4]; persistent fatigue, hot flashes, and reduced sex drive [4]
High	Obesity-related overproduction [4]; increased tumor growth in breast and endometrial cancers [4]

Figure 2: Balanced estrone levels support bone and vascular health, while irregularities pose various risks.

Testing and Management

Healthcare providers may use blood tests to monitor estrone levels [4], particularly in high-risk scenarios.

When testing is required

• Cancer management. Monitoring levels during breast or endometrial cancer treatment (for example, with aromatase inhibitors).

• Prostate treatment. Males undergoing testosterone-reduction therapy (see androgen deprivation therapy) for prostate cancer may have their estrone checked [4].

• Menopause evaluation. To assess persistent symptoms that interfere with daily life [4].

Clinical applications

Synthetic estrone is available in laboratory-made forms, such as hormone therapy creams, to treat severe menopause symptoms [4]. (Compare options in our guide to menopause hormone therapy.)

Figure 3: Regular monitoring and healthy lifestyle choices help maintain optimal hormonal balance.

Key Takeaways

Estrone may be the "weakest" estrogen, but its role in the human body is far from minor. From supporting bone density to serving as the primary estrogen after menopause, E1 is a critical player in long-term health. By understanding how factors like body weight influence its production, individuals can take proactive steps to manage their hormonal balance. Regular consultations with healthcare providers ensure that any irregularities are addressed before they lead to more significant health challenges.

Take the Next Step

If you are experiencing persistent fatigue or bone health concerns after menopause, speak with your healthcare provider about checking your hormone levels.

Related reading: Estrogen-Dependent Cancers · Understanding Menopause · Low Testosterone · Luteinizing Hormone (LH) · The Endometrium

Frequently Asked Questions

1. What is estrone (E1)?

Estrone is one of the three main types of estrogen hormones and is considered the weakest form.

2. Do males have estrone?

Yes, both males and females produce estrone, though males typically have much lower levels.

3. Where is estrone made?

It is produced in the adrenal glands and body fat in everyone, and also in the ovaries in females.

4. Why is estrone important after menopause?

After menopause, estrone becomes the main type of estrogen the body makes naturally, though small amounts of estradiol are still made.

5. Can the body change estrone into other hormones?

Yes, the body can convert estrone into estradiol, a stronger form of estrogen, when needed.

6. How does body fat affect estrone?

Since estrone is produced in adipose (fat) tissue, being overweight can lead to higher levels of the hormone.

7. What are the risks of high estrone?

High levels may increase the growth of tumors in breast and endometrial cancers.

8. What happens if estrone is too low?

Low levels can increase the risk of osteoporosis and cause symptoms like hot flashes and fatigue.

9. What is a normal estrone level for a female?

Normal levels vary by cycle phase, ranging from 15 to 250 pg/mL, and drop to 15-55 pg/mL after menopause. Ranges can differ between laboratories.

10. Is estrone used as a medication?

Yes, synthetic estrone is used in some hormone therapy creams to treat menopause symptoms.

References

1. Key T, Appleby P, Barnes I, Reeves G; Endogenous Hormones and Breast Cancer Collaborative Group. Endogenous sex hormones and breast cancer in postmenopausal women: reanalysis of nine prospective studies. J Natl Cancer Inst. 2002;94(8):606-616. doi:10.1093/jnci/94.8.606. PMID: 11959894.

2. Key TJ, Appleby PN, Reeves GK, et al. Steroid hormone measurements from different types of assays in relation to body mass index and breast cancer risk in postmenopausal women: reanalysis of eighteen prospective studies. Steroids. 2014;99(Pt A):49-55. doi:10.1016/j.steroids.2014.09.001. PMID: 25304359.

3. Engin A. Obesity-associated breast cancer: analysis of risk factors and current clinical evaluation. Adv Exp Med Biol. 2024;1460:767-819. doi:10.1007/978-3-031-63657-8_26. PMID: 39287872.

4. Cleveland Clinic. Estrone. Cleveland Clinic Health Library. Medically reviewed; last updated April 14, 2026. https://my.clevelandclinic.org/health/body/22398-estrone

Medical Disclaimer

This article is for informational purposes only and does not constitute medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read here.