January 16, 2014

The Problem With Estrogen Metabolite Ratios

Is it time for us to let go?
The theory that estrogen metabolite ratios are predictive of cancer risk is failing in these studies to be predictive. This current paper is one more in a series that call this hypothesis into question. It may be time for our profession to reassess the theory and rethink the clinical practices we have adopted based on these assumptions.


Mackey RH, Fanelli TJ, Modugno F, et al. Hormone therapy, estrogen metabolism, and risk of breast cancer in the Women's Health Initiative Hormone Therapy Trial. Cancer Epidemiol Biomarkers Prev. 2012 Nov;21(11):2022-2032.


A prospective case-controlled study nested within the women's Health Initiative Hormone Trials (WHI-HT). From this large cohort, confirmed breast cancer cases were matched to controls by age and ethnicity. Using stored blood serum, biomarkers were measured at baseline and also, for those receiving active treatment, at 1 year.


Study included 845 women with confirmed breast cancer. They were matched to 1,690 control patients by age and ethnicity.

Study Medication and Dosage

Women in the WHI-HT study were receiving hormone therapies, estrogen, estrogen plus progesterone, or placebo.

Outcome Measures

Using stored blood serum, measurements of 16α-hydroxyestrone and 2-hydroxyestrone levels were measured by EIA at baseline and, for those randomized to active treatment (n=1,259), at 1 year.

Key Findings

In women using estrogen and progesterone together, 16α-hydroxyestrone levels increased slightly more than in women using estrogen alone (55.5 vs 43.5 pg/ml). Both groups of women had significant increases (~300 pg/ml) in 2-hydroxyestrone levels. There was a modest association between higher baseline levels of 2-hydroxyestrone and larger 2:16 ratio with breast cancer risk. Those diagnosed with estrogen receptor (ER)+/progesterone receptor (PR)+ breast cancer had higher baseline 16α-hydroxyestrone levels. For those randomized to treatment with hormone replacement therapy, breast cancer risk was associated with greater increases in 2-hydroxyestrone and larger 2:16 ratio, but associations were not significant. Increasing amounts of 16α-hydroxyestrone that resulted from hormone replacement therapy were not associated with breast cancer.

Practice Implications

The theory that estrogen metabolite ratios (EMRs), in particular the ratio between 2-hydroxyestrone and 16-α-hydroxyestrone, are predictive of cancer risk is failing in these studies to be predictive. This current paper is one more in a series that call this hypothesis into question. It may be time for our profession to reassess the theory and rethink the clinical practices we have adopted based on these assumptions.
The focus of this EMR theory is the ratio between 2 estrogen breakdown products, 2-hydroxyestrone and 16-α-hydroxyestrone. The hypothesis is that 2-hydroxyestrone is relatively protective, whereas 16-α-hydroxyestrone is harmful, particularly in hyperproliferative disorders such as cysts and fibromas. High levels of 16-α-hydroxyestrone or a decreased 2:16 ratio supposedly increase risk of hormone-dependent cancers.
In the case of estrogen metabolites, the theory that the 2-hydroxy form is good for women and the 16-alpha-hydroxy form is bad is not holding up.
Following this theory, it has become a common strategy to attempt to shift the ratio of these estrogen metabolites, assuming that this will be protective against hormone-related cancer occurrence, recurrence, and progression. 
This theory is summed up on the popular website NaturalNews.com:
“The estrogen compounds called 2-hydroxyestrone and 16-α-hydroxyestrone are by far the most important for breast health. 2-hydroxyestrone is considered 'The Good Estrogen' because its presence doesn't seem to increase breast cancer risks, and MAY even be protective against it. However, 16-α-hydroxyestrone is considered 'The Bad Estrogen' because its presence seems to INCREASE breast cancer risk and has even been called a cancer CAUSING agent! All women have both estrogens, but each woman has a different RATIO, and this ratio is more important to health than the total AMOUNTS of the estrogens.”1
The problem is, research is not substantiating these ideas.
A paper published in October 2011 in the British Journal of Cancer deserves our attention. Zeleniuch-Jacquotte et al tested this “2 is good and 16α is bad” hypothesis as it relates to endometrial cancer and found no support. They conducted a case-controlled study of 179 cases and 336 controls. Levels of 2 and 16-α-hydroxyestrone were measured. Risk of endometrial cancer was calculated and compared to these levels. No significant association was observed for the 2 versus 16-α ratio. Their results did not support the hypothesis that “greater metabolism of estrogen through the 2-hydroxy pathway, relative to the 16α-hydroxy pathway, protects against endometrial cancer.”2
A February 2011 a meta-analysis by Obe et al asked whether estrogen metabolite ratios change breast cancer risk. Data from 9 prior studies comprising 682 premenopausal and 1,189 postmenopausal breast cancer cases was combined. In comparing the “highest compared with the lowest quantile of urinary EMR [estrogen metabolite ratio], nonsignificant associations suggested at best a weak protective effect in premenopausal but not in postmenopausal breast cancer (range of odds ratios: 0.50–0.75 for premenopausal and 0.71–1.31 for postmenopausal). ... Circulating serum/plasma EMR was not associated with breast cancer risk. … Results of the prospective studies do not support the hypothesis that EMR can be used as a predictive marker for breast cancer risk.”3
Return to the abstract featured in this review. A modest increase in risk for breast cancer was found in those women with a higher 2-hyrdroxyestrone level at baseline. Increased 16-α-hydroxyestrone was not associated with greater risk. This is backwards of what the EMR theory predicts. 
A 2008 paper is also worth mention. Heather Eliassen and colleagues at Harvard’s Channing Laboratory reported on their own attempt to sort out the impact of these estrogen metabolites.4
They conducted a prospective case-control study using data and blood samples from the Nurses' Health Study. They tested for 2-hydroxyestrone and 16-α-hydroxyestrone in blood samples collected between 1989 and 1990 and compared levels in 340 cases of breast cancer with 677 matched controls. Neither estrogen metabolite appeared to change breast cancer risk. Nor did the ratio between the two metabolites make a significant difference.
There was however a significant positive association observed for the 2-hydroxyestrone and the 2:16 ratio among women with ER-/PR- tumors. High numbers for either were associated with triple the relative risk for this small subgroup of breast cancer patients. Again these results are backwards from what the theory predicts.
While these results don’t support the basic hypothesis that 2-hydroxyestrone lowers breast cancer risk nor that the 2 versus 16-α ratio is predictive of risk, the significant link found with hormone receptor negative breast cancer is worth noting. This unexpected observation might argue in favor of aromatase inhibition even in hormone receptor negative breast cancer patients.
There is some evidence that 16-α-hydroxyestrone is protective in other ways. A 2009 study in the American Journal of Hypertension reported that there is an inverse association between 16-α-hydroxyestrone and systolic blood pressure in women; that is, the higher the 16-α levels, the lower their blood pressure.5 Most would consider this a good, not bad, association.
A July 2011 paper by Patel et al reported 16α-hydroxyestrone levels were affected by fiber intake. Soluble fiber has a greater impact than dietary fiber. Dietary fiber is higher in grains and beans, while fruits and vegetables provide more soluble fiber. CYP1A2, one of the cytochrome P450 enzymes made by the liver and that is important in the formation of 16α-hydroxyestrone, is increased by soluble fiber in the diet. Patel hypothesizes that women who eat a lot of fruits and vegetables have lower systolic blood pressures because the soluble fiber in these foods increases CYP1A2, which in turn increases 16-α-hydoxyestrone.6 This sounds like a positive effect from increasing 16-α-hydroxyestrone levels or decreasing the 2:16 ratio.
2-hydroxyestrone levels are affected by genetics and lifestyle factors, including weight; smoking; and consumption of hydroxybenzoic acid, anthocyanidins, wine, and caffeine.7 Exercise generally doesn’t increase the 2:16 ratios except in women with very low initial 2:16 ratios; for this subgroup, losing weight and exercising does seem to shift production toward greater 2-hydroxyestrone. 8,9
As naturopathic physicians, we are often ahead of the curve in translating new theories published in the scientific literature into clinical protocols for use with our patients. This “early adopter” tendency has its merits. We sometimes find ways to help our patients when “regular” medicine has yet to develop a treatment. Because we limit our interventions to relatively nontoxic, low-risk therapies, we set a relatively low requirement of proof before experimenting with new ideas. We can justify our experimentation with a “might help and won’t hurt” summation of risk analysis. If we were using more dangerous therapies, we would surely raise the bar, asking for stronger evidence before trying a new idea.
Being an early adopter does come with responsibility; if a new idea, doesn’t pan out, we need to abandon it and we need to let others know. But it’s easier for us to take on new ideas than it is to let go of them. In the case of estrogen metabolites, the theory that the 2-hydroxy form is good for women and the 16-α-hydroxy form is bad is not holding up. Growing evidence suggests that there is little correlation between these hormones and cancer risk; the situation is more complex than we first thought.
It may be time that we let this idea go.

Categorized Under


  1. Knox K. Ratio of good to bad estrogens influences your breast cancer risk. Natural News. October 13, 2009. http://www.naturalnews.com/027227_cancer_breast_estrogen.html. Accessed August 31, 2013.
  2. Zeleniuch-Jacquotte A, Shore RE, Afanasyeva Y, et al. Postmenopausal circulating levels of 2- and 16α-hydroxyestrone and risk of endometrial cancer. Br J Cancer. 2011;105(9):1458-1464.
  3. Obi N, Vrieling A, Heinz J, Chang-Claude J. Estrogen metabolite ratio: Is the 2-hydroxyestrone to 16α-hydroxyestrone ratio predictive for breast cancer? Int J Womens Health. 2011;3:37-51.
  4. Eliassen AH, Missmer SA, Tworoger SS, Hankinson SE. Circulating 2-hydroxy- and 16alpha-hydroxy estrone levels and risk of breast cancer among postmenopausal women. Cancer Epidemiol Biomarkers Prev. 2008;17(8):2029-2035.
  5. Masi CM, Hawkley LC, Xu X, Veenstra TD, Cacioppo JT. Serum estrogen metabolites and systolic blood pressure among middle-aged and older women and men. Am J Hypertens. 2009;22(11):1148-1153.
  6. Patel S, Hawkley LC, Cacioppo JT, Masi CM. Dietary fiber and serum 16α-hydroxyestrone, an estrogen metabolite associated with lower systolic blood pressure. Nutrition. 2011;27(7-8):778-781.
  7. Sowers MR, Crawford S, McConnell DS, et al. Selected diet and lifestyle factors are associated with estrogen metabolites in a multiracial/ethnic population of women. J Nutr. 2006;136(6):1588-1595.
  8. Campbell KL, Westerlind KC, Harber VJ, Bell GJ, Mackey JR, Courneya KS. Effects of aerobic exercise training on estrogen metabolism in premenopausal women: a randomized controlled trial. Cancer Epidemiol Biomarkers Prev. 2007;16(4):731-739.
  9. Westerlind KC, Williams NI. Effect of energy deficiency on estrogen metabolism in premenopausal women. Med Sci Sports Exerc. 2007;39(7):1090-1097.