Chrysin (5,7-Dihydroxyflavone) is a flavonoid extracted from the plant Passiflora coerulea, a member of the passion flower family. It is promoted in bodybuilding to be an effective inhibitor of an enzyme known as aromatase which causes the conversion of testosterone into estradiol and androstenedione into estrone. In many in vitro (artificial environment) studies, chrysin has been shown to be a very potent and natural inhibitor of human estrogen aromatase. Its ability to inhibit the aromatization of androstenedione and testosterone to estrogen has been well demonstrated in lab tests.
Because of this, Chrysin has been heavily promoted as an inhibitor of aromatase, and widely sold in the supplement industry despite the fact that no in vivo (in a living organism) studies have been able to substantially prove its effectiveness in human subjects. At least in the lengthy research I did, I was unable to find any in vivo studies to show its efficacy in human subjects, but rather, I find many studies coming to similar conclusions showing that Chrysin did little to affect the testosterone levels of the subjects. As well, there are no studies to support that Chrysin makes the use of testosterone and related steroids less likely to produce estrogenic effects.
Despite this, various studies have found Chrysin to significantly improve overall sexual function and increase sperm count. Our discussion on Chrysin that follow will be divided into two sections: 1) studies demonstrating the aromatase inhibiting abilities of Chrysin, and 2) studies demonstrating that Chrysin did little to affect testosterone levels in living subjects.
Chrysin Studies - A Closer Look at Chrysin
The ability of chrysin to inhibit aromatase activity sounds swell for bodybuilders, and any male concerned with their testosterone levels. Especially when aromatase levels rise with age, this increase can cause an imbalance of estrogen and testosterone in men - in addition to decreased production of testosterone (with age), the increase in aromatase causes men to convert some of the testosterone they produce to estrogen. Not a desirable effect by any means. This partially explains the interest in Chrysin for its ability to inhibit aromatase.
While there is no doubt in the ability of chrysin to inhibit aromatase activity, certain doubts arise when the efficacy of Chrysin in real human subjects is put to the test - and this could be due to several factors such as poor bioavailability, and/or poor oral absorption as we will see later demonstrated in various studies. Below are 2 studies done relating to inhibition of aromatase activity by flavonoids, and as it turns out, Chrysin was found to be one of the most potent inhibitors of aromatase.
Inhibition of aromatase activity by flavonoids Jeong HJ, Shin YG, Kim IH, Pezzuto JM.
Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, 60612, USA.
Summary: 28 randomly selected flavonoids were screened for inhibitory effects against aromatase. Over half of the flavonoids significantly inhibited aromatase activity. Chrysin, along with two other flavonoids, was found to be the most potent.
Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogens Kao YC, Zhou C, Sherman M, Laughton CA, Chen S.
Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
Summary: This study looked at the inhibition profiles of 4 flavones (including Chrysin), 2 isoflavones, 1 flavanone, and 1 naphthoflavone. Along with computer modeling, binding characteristics to inhibit human aromatase was obtained. The study concluded that the flavones (Chrysin) were significantly more potent than the other groups.
Does Chrysin Work for Humans?
While these studies work well to demonstrate the aromatase inhibiting properties of Chrysin, they did not involve real human subjects. They merely substantiate the fact that Chrysin is an effective and potent aromatase inhibitor. In looking further at in vivo studies involving living subjects, it becomes clear that there is a gap between lab results and real world results. In the various studies I looked at, I was unable to find a study that showed the effectiveness of Chrysin in human subjects. If you've used Chrysin supplements, please share your feedback on Chrysin here. Below are several such studies.
Effects of chrysin on urinary testosterone levels in human males Gambelunghe C, Rossi R, Sommavilla M, Ferranti C, Rossi R, Ciculi C, Gizzi S, Micheletti A, Rufini S.
Department of Clinical and Experimental Medicine, Division of Sports Medicine-Laboratorio delle Attivita Motorie e Sportive, University of Perugia, Perugia, Italy.
Summary: The study was designed to verify if daily treatment with propolis and honey naturally containing chrysin would modify urinary concentrations of testosterone in male subjects for 21 days. The researchers theorized that the aromatase inhibiting properties of Chrysin should block the conversion of "androgens into estrogens with a consequent increase of testosterone, eventually measurable in urine samples". However, the obtained data showed no changes in the testosterone levels in the male subjects after 7, 14, and 21 days of treatment compared with baseline values. They could only conclude that the 21 day treatment using propolis and honey containing chrysin had no effects on the testosterone in the male subjects.
The only issue I would have with the above study is that they used propolis and honey naturally containing chrysin, it did not involve supplementing the subjects directly with Chrysin supplements. Below is another study on Chrysin using human subjects.
Transport of the flavonoid chrysin and its conjugated metabolites by the human intestinal cell line Caco-2.Walle UK, Galijatovic A, Walle T.
Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston 29425, USA.
Summary: The study examined the intestinal transport of chrysin to determine its oral bioavailability. From their observations, the researchers concluded that although chrysin has favorable membrane transport properties, its intestinal absorption is limited by surprisingly efficient glucuroidation (process where the human body excretes a large variety of molecules).
This is one of the many studies I found showing that Chrysin's effectiveness in human subjects is limited due to its relatively poor absorption and/or bioavailability. While these studies show that poor bioavailability of Chrysin leads to diminished aromatase inhibiting effects in humans, its not enough to count Chrysin out as a potential testosterone enhancing supplement. Studies have also found chrysin to be a potent sexual enhancer. Below is one such study:
Beneficial effects of chrysin and benzoflavone on virility in 2-year-old male rats Dhawan K, Kumar S, Sharma A.
Pharmacognosy Division, University Institute of Pharmaceutical Sciences, Panjab University, Chandigarh-160014, India.
Summary: Chrysin and benzoflavone moiety was administered to 2 year old male rats for a period of 30 days. After these treatments, the researchers noted a significant improvement in overall sexual function in the rats compared to the control group. The treated group showed increased libido, increased sperm count, greater fertilization potential, and greater litter size compared to the control group.
Chrysin Side Effects
There are no reported side effects of using Chrysin. Non of the studies I read reported any side effects, and as well, there are no studies that have been done to determine Chrysin side effects, if any at all.