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2-Hydroxyestrone (2-Hydroxyestrone) is a metabolite of estrone, one of the three main estrogens produced by the human body.  It has been associated with various health implications due to its relationship with other metabolites of estrone.

Laboratory testing for 2-Hydroxyestrone can provide valuable insights into an individual's estrogenic activity and potential risks related to estrogen dominance. 

This article delves into the significance of 2-Hydroxyestrone as a biomarker, exploring its definition, functions, laboratory testing methods, clinical applications, and implications for healthcare. Additionally, strategies for lowering 2-Hydroxyestrone levels and optimizing health outcomes are discussed. 

What is 2-Hydroxyestrone?

2-Hydroxyestrone Definition and Overview

2-Hydroxyestrone is a metabolite of estrogen called a catechol estrogen.  Estrogen is a steroid sex hormone primarily produced in the ovaries in females and smaller amounts in the adrenal glands and adipose tissue in both sexes.  [11.] 

Estrogen is primarily processed by the CYP family of enzymes (although certain other enzymes are involved, often hydroxylases), which convert it to estrone (E1), estradiol (E2), and estriol (E3).  

Estrone (E1) is further processed to 2-hydroxyestrone, 4-hydroxyestrone, or 16-hydroxyestrone via the same CYP family of enzymes.  Each of these forms of estrone have different health implications.  

2-Hydroxyestrone is a hydroxylated form of estrone that is converted from estrone via the CYP1A1 enzyme.  It is produced via hydroxylation at the 2nd carbon position.

Catechol estrogens  [21.] 

Catechol estrogens, a type of estrogen metabolite, undergo processes known as redox cycling, producing reactive oxygen species (ROS) such as hydrogen peroxide and hydroxyl radicals. 

These metabolites, including 2-hydroxyestradiol, 4-hydroxyestradiol, 4-hydroxyestrone, and 2-hydroxyestriol, are implicated in the development of breast cancer due to their mutagenic properties and ability to cause DNA damage. 

Unlike their parent compounds (estradiol, estrone, estriol), these catechol estrogens actively participate in redox cycling, significantly contributing to oxidative stress within breast epithelial cells. 

2-Hydroxyestrone Functions and Physiological Roles

Overview of Functions of Estrogens  [8., 19.]

Estrogens play critical roles in various physiological processes including regulating reproductive function and the menstrual cycle, bone health, cardiovascular function, and cognitive function and mood.  

Additionally, estrogen signaling influences lipid metabolism, glucose homeostasis, and immune function.  

It also affects skin elasticity, hair growth, body weight, and fat distribution, while contributing to sexual health by enhancing vaginal wall thickness and lubrication. Additionally, estrogen is crucial for breast development during puberty and preparing for lactation.

Overview of Estrone  [1., 8.]

Estrone (E1) is one of the three main estrogens produced in the human body, alongside estradiol (E2) and estriol (E3). It becomes the predominant form of estrogen in postmenopausal women. 

Estrone is primarily synthesized in adipose tissue through the aromatization of androstenedione, an androgen produced by the adrenal glands and the ovaries. This process becomes especially important after menopause when ovarian estrogen production declines.

Estrogens and Their Interactions with Receptors  [8.]

The actions of estrogens in the body are influenced by the specific structure of each estrogen molecule, the type of estrogen receptor it binds to, and the cellular context. 

Estrogens exert their effects by binding to estrogen receptors, which are part of the nuclear hormone receptor superfamily. These receptors exist mainly in two forms, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), each encoded by different genes and varying structurally, particularly in their ligand-binding domains. 

This difference in structure affects their affinity for various ligands; for instance, some estrogens and phytoestrogens preferentially bind ERβ, whereas others have a higher affinity for ERα.

Once bound to an estrogen, the receptor undergoes a conformational change, allowing it to dissociate from chaperone proteins and move into the nucleus where it binds to DNA at sites known as estrogen-response elements.  

This binding can either activate or repress the transcription of target genes depending on the presence of coactivators or corepressors in the complex. 

The distribution of estrogen receptors varies across different tissues, which partly explains the tissue-specific effects of estrogen. For example, ERα is predominantly found in reproductive tissues like the endometrium, while ERβ is more common in non-reproductive tissues such as bone and brain. 

This selective expression and the unique interaction of estrogens with their receptors underpin the diverse physiological roles of estrogens, from reproductive functions to their roles in bone density and cardiovascular health.

2-Hydroxyestrone’s Role in the Human Body

As an estrogen metabolite, 2-OH estrone also holds some estrogenic activity in its ability to activate estrogen receptors, although it does so less strongly than other forms of estrogen or other estrogen metabolites.  For this reason, it has traditionally been viewed as being the safest, least carcinogenic estrogen metabolite.  [20.]

2-Hydroxyestrone exhibits significant biological effects that differentiate it from its precursor estrone, particularly in its interaction with estrogen receptors (ERs) and impact on cell proliferation and carcinogenesis. 

Unlike E1, which typically promotes cell proliferation, 2-Hydroxyestrone has been observed to inhibit the proliferation of breast cancer cells (MCF-7), suggesting anti estrogenic properties.  [20.]

Specifically, 2-Hydroxyestrone downregulates key proteins in the mammalian target of rapamycin (mTOR) and protein kinase B (Akt) pathways, which are crucial for cell proliferation. This leads to a decrease in cancer cell growth and enhanced anti-inflammatory and anti-oxidative responses.  [20.]

However, additional research is emerging that creates a more nuanced perspective of 2-Hydroxyestrone’s effects on health and cancer risk.  

2-OH Estrone and Estrogen Receptor-Positive and Breast Cancer Risk  [6., 13.]

2-hydroxyestrone (2OHE1) and 16α-hydroxyestrone (16αOHE1), both processed by enzymes CYP1A1 and CYP1B1 in the breast, impact cell proliferation and carcinogenesis differently. 

2OHE1 has been thought to have anti estrogenic properties due to its weaker binding to estrogen receptors and is linked with normal cell differentiation and apoptosis, whereas 16αOHE1 binds covalently to receptors, promoting abnormal cell growth.

The ratio of these metabolites (2OHE1 to 16αOHE1) has long been used as a marker to inform an individual’s risk for breast cancer:  it's hypothesized that a lower ratio could be associated with a higher risk of breast cancer. 

However, systematic reviews covering nine studies (six prospective and three retrospective) reveal that this estrogen metabolite ratio (EMR) shows, at most, a weak protective effect against breast cancer in premenopausal women and no significant association in postmenopausal women. The EMR's predictiveness for breast cancer risk remains inconclusive, particularly when considering receptor subtypes.  [13.] 

This review suggests that future research should focus on a broader spectrum of estrogen metabolites, including potentially significant ones like 4-hydroxyestrone, to fully understand their roles in breast cancer risk.

In a nested case-control study within the Nurses' Health Study, which included 340 breast cancer cases and 677 controls, no significant association was found between the concentrations of these metabolites and overall breast cancer risk. This included examining the individual metabolites and the ratio between 2-OH estrone and 16α-OH estrone.  [6.] 

However, specific findings showed that among women with estrogen receptor-negative and progesterone receptor-negative (ER-/PR-) tumors, there was a significant positive association with higher levels of 2-OH estrone and the ratio of 2:16α-OH estrone. These results suggest that the impact of estrogen metabolites may vary based on the hormone receptor status of the tumor.

The study highlights that while general links between these metabolites and breast cancer risk in postmenopausal women are not supported, the observed associations in certain subgroups, such as those with ER-/PR- tumors, warrant further investigation. This could help clarify the role of estrogen metabolism in the development of specific types of breast cancer.

Laboratory Testing for 2-Hydroxyestrone

Overview of Testing, Sample Collection and Preparation

Urine samples are commonly used for 2-Hydroxyestrone testing.  

Estrogen metabolites can be excreted in the urine, making it a reliable method for testing estrogen detoxification and comparing ratios of estrogen metabolites.  Urine testing specifically assesses phase I estrogen detoxification, and it can also be used to assess phase II methylation detoxification.    

Urine collection can be easier and less stressful for patients compared to blood draws, as samples can be collected at home without the need for a clinical setting.  Additionally, urinary levels can reflect longer-term hormone exposure rather than the transient levels often seen in blood, as it reflects detoxification patterns (rather than providing snapshots of levels in the bloodstream).

Interpretation of 2-OH Estrone Test Results

Reference Range for 2-OH Estrone

It is important to consult with the lab company providing testing for 2-OH estrone levels.  For reference, one lab provides the following reference range for urine 2-OH estrone levels:  [15.]

For cycling women in the luteal phase: 5.1-13.1 ng/mg

For postmenopausal women not supplementing with hormones: 0.3-2.0 ng/mg

Optimal Levels of 2-Hydroxyestrone

Hormones never act alone, and their effects are nuanced.  Optimal levels of 2-hydroxyestrone in urine tests vary depending on individual health conditions, gender, and age.   2-Hydroxyestrone is still considered the preferred estrogen detoxification pathway.

One recommendation is that 60-80% of a woman's circulating estrogen utilize the 2-OH pathway; that 13-30% utilizes the 16-OH pathway; and that the remaining 7.5-11% utilizes the 4-OH pathway.  [14.]

Health professionals often recommend that women remain within the reference range of 5.1-13.1 ng/mg in urine samples for cycling women, or 0.3-2.0 ng/mg in urine samples for postmenopausal women.  However, a professional's recommendation will be affected by many factors including the patient’s overall health, detoxification capacity, personal and family health history, time of life, diet and lifestyle, medications, and other factors.  

Regular monitoring through urinary tests is essential to ensure that the metabolite levels are within a safe range, thereby reducing the potential for DNA damage and promoting better hormonal balance and overall health.

Clinical Significance of High 2-Hydroxyestrone Levels

In postmenopausal women receiving hormone replacement therapy, elevated levels of 2-OH E1 may indicate an excessive amount of hormone supplementation which may be causing unwanted overstimulation of estrogen-sensitive tissue at the breasts and endometrium.  

These women should have their dosages assessed by a healthcare professional, and estrogen detoxification support may be considered.   

Premenopausal women with elevated levels of 2-Hydroxyestrone should be assessed by a healthcare professional, including a comprehensive assessment of male and female sex hormones, as well as considering adrenal and thyroid hormone levels.  Additionally, estrogen detoxification support may be considered.  

Premenopausal women, or women supplementing with estrogen who complain of estrogen excess symptoms, should be assessed for estrogen and estrogen metabolite levels.  

See below for more information on natural methods to promote hormone balance.   

Clinical Significance of Low 2-Hydroxyestrone Levels

Typically, declining levels of estrogen and its metabolites are seen postmenopausally.  Testing of estrogen metabolites may be recommended for women complaining of menopausal symptoms.  

Additionally, postmenopausal women with a family or personal history of osteoporosis or low bone mineral density should consider testing their estrogen and estrogen metabolite levels.  

2-Hydroxyestrone Related Biomarkers to Consider

Several other biomarkers are associated with estrogen metabolism and activity.  Other estrogen metabolites including 16-hydroxyestrone (16-OH-E1) and 4-hydroxyestrone (4-OH-E1), as well as estrone (E1), estradiol (E2), and estriol (E3) levels should be considered.  

16-Hydroxyestrone (16-OH estrone)

16-Hydroxyestrone (16-OH E1) is a metabolite of estrone, one of the three main naturally occurring estrogens in the human body.  

Unlike some other estrogen metabolites, 16-OH E1 exhibits relatively strong estrogenic activities. It binds to estrogen receptors, potentially influencing estrogen-responsive gene expression and cellular functions.

 This metabolite has been associated with various physiological effects and is implicated in different health conditions, including increased risks for certain types of cancers due to its potent estrogenic properties.

4-Hydroxyestrone (4-OH estrone)

4-OH estrone is another metabolite of estrone with strong estrogenic properties and potential carcinogenic effects. 

 Specifically, 4-OH estrone is known for its potential to form quinones that can directly damage DNA and generate reactive oxygen species, increasing the risk of mutagenesis.

Measuring 4-OH estrone alongside 16-OH estrone and 2-OH estrone can help assess the overall estrogenic and carcinogenic potential within the body.

Estrone (E1)

Estrone is a weaker estrogen compared to estradiol but is prevalent in postmenopausal women and can be converted back to estradiol. 

Testing for estrone is important for understanding the overall estrogenic activity, especially in postmenopausal women who are at increased risk for estrogen-sensitive cancers.

Estradiol (E2)

Estradiol is the most potent estrogen and has significant implications for bone density, reproductive health, and cardiovascular health.  Monitoring estradiol levels is essential for assessing reproductive health and menopausal status, and for managing hormone replacement therapy effectively.

Estriol (E3)

Estriol is a weak estrogen predominantly produced during pregnancy. Outside of pregnancy, its levels are very low, but it has been suggested to have protective effects against breast cancer. 

Testing for estriol, especially in non-pregnant states, might provide additional insights into estrogenic activity and potential protective mechanisms against estrogen-related pathologies.

Natural Ways to Promote Hormone Balance

It is always essential to work with a qualified healthcare professional in any case of hormone imbalance.  The following diet and lifestyle measures have been shown to naturally promote healthy hormone balance:

Dietary Fiber Increase: consuming more fiber helps bind estrogen in the digestive tract, promoting its excretion and reducing reabsorption.  [7.]  

Interestingly, one study of 240 women also showed a correlation between increased fiber intake and anovulation, possibly due to lower estrogen levels.  [7.]

Cruciferous Vegetables: foods like broccoli, cauliflower, and Brussels sprouts contain indole-3-carbinol, which aids in detoxifying excessive estrogen and optimizing hormone balance.  [3.] 

Regular Exercise: physical activity can help balance hormones by improving metabolism and reducing fat, which is significant since body fat can produce and store estrogen.  [17.]

Probiotics and Gut Health: a healthy gut flora supports proper digestion and detoxification processes, including the breakdown, elimination and balance of hormones like estrogen.  [10.]

Limit Alcohol and Caffeine: reducing intake of substances that can impair liver function helps ensure the liver effectively processes and removes excess hormones.  [16.]

Stress Management: stress may have an impact on estrogen levels and metabolism; techniques such as yoga, meditation, or even simple breathing exercises can reduce cortisol levels and help maintain a healthy hormonal balance.  [2.]

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