Chrysin is a flavonoid that occurs naturally in plants such as the passionflower, silver linden, some geranium species, and in honey and bee propolis (1-3). Athletes are interested in chrysin for bodybuilding due to its potential effect on testosterone levels. In vitro research shows that chrysin might inhibit aromatase and decrease aromatisation of androstenedione and testosterone to oestrogen and dihydrotestosterone (4), but research in humans shows that chrysin does not increase testosterone levels when used in combination with androgen precursors such as androstenedione and dehydroepiandrosterone (DHEA) (5).
Researchers are also interested in chrysin due to several potential anticancer properties. Chrysin seems to increase glucuronidation by inducing UDP-glucuronosyltransferase 1A1 (UGT1A1), which might reduce the bioavailability of dietary carcinogens (3,6). Chrysin might also might inhibit cytochrome P450 1A1 (CYP1A1) and 1A2 (CYP1A2), which could prevent activation of potentially carcinogenic food-derived heterocyclic aromatic amines (7503,8172). There is also preliminary evidence that chrysin might decrease oestrogen synthesis by acting as an aromatase (oestrogen synthetase) inhibitor, similar to the breast cancer drugs anastrozole (Arimidex) and letrozole (Femara) (7,8).
Chrysin might also have antioxidant properties (9). Chrysin appears to inhibit xanthine oxidase, suggesting potential use for preventing oxidative injury in ischaemia-reperfusion and treating gout (10).
Chrysin might have activity against the human immunodeficiency virus (HIV). It appears to block HIV transcriptional activation, possibly by blocking casein kinase II (CKII), an enzyme that seems to regulate HIV transcription (11,12).
There's also some evidence that chrysin might act as a sunscreen. Chrysin-fed experimental animals are protected from contact hypersensitivity induced by ultraviolet (UV) radiation (13).
There is some preliminary evidence that chrysin can bind benzodiazepine receptors and might have some anxiolytic effects. Some researchers call it a partial benzodiazepine agonist because it does not seem to affect memory and does not have anticonvulsant, muscle relaxant, or sedative activity (14-17).
1. Salgueiro JB, Ardenghi P, Dias M, et al. Anxiolytic natural and synthetic flavonoid ligands of the central benzodiazepine receptor have no effect on memory tasks in rats. Pharmacol Biochem Behav 1997;58:887-91.
2. Williams CA, Harborne JB, Newman M, et al. Chrysin and other leaf exudate flavonoids in the genus Pelargonium. Phytochemistry 1997;46:1349-53.
3. Galijatovic A, Otake Y, Walle UK, Walle T. Extensive metabolism of the flavonoid chrysin by human Caco-2 and Hep G2 cells. Xenobiotica 1999;29:1241-56.
4. Kellis JT Jr, Vickery LE. Inhibition of human estrogen synthetase (aromatase) by flavones. Science 1984;225:1032-4.
5. Brown GA, Vukovich MD, Reifenrath TA, et al. Effects of anabolic precursors on serum testosterone concentrations and adaptations to resistance training in young men. Int J Sport Nutr Exerc Metab 2000;10:340-59.
6. Galijatovic A, Otake Y, Walle UK, Walle T. Induction of UDP-glucuronosyltransferase UGT1A1 by the flavonoid chrysin in Caco-2 cells--potential role in carcinogen bioinactivation. Pharm Res 2001;18:374-9.
7. Kao YC, Zhou C, Sherman M, et al. Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogens: A site-directed mutagenesis study. Environ Health Perspect 1998;106:85-92.
8. Jeong HJ, Shin YG, Kim IH, Pezzuto JM. Inhibition of aromatase activity by flavonoids. Arch Pharm Res 1999;22:309-12.
9. Breinholt V, Lauridsen ST, Dragsted LO. Differential effects of dietary flavonoids on drug metabolizing and antioxidant enzymes in female rat. Xenobiotica 1999;29:1227-40.
10. Nagao A, Seki M, Kobayashi H. Inhibition of xanthine oxidase by flavonoids. Biosci Biotechnol Biochem 1999;63:1787-90.
11. Critchfield JW, Coligan JE, Folks TM, Butera ST. Casein kinase II is a selective target of HIV-1 transcriptional inhibitors. Proc Natl Acad Sci U S A   
12. Wang HK, Xia Y, Yang ZY, et al. Recent advances in the discovery and development of flavonoids and their analogues as antitumor and anti-HIV agents. Adv Exp Med Biol 1998;439:191-225.  
13. Steerenberg PA, Garssen J, Dortant P, et al. Protection of UV-induced suppression of skin contact hypersensitivity: a common feature of flavonoids after oral administration? Photochem Photobiol 1998;67:456-61.
14. Salgueiro JB, Ardenghi P, Dias M, et al. Anxiolytic natural and synthetic flavonoid ligands of the central benzodiazepine receptor have no effect on memory tasks in rats. Pharmacol Biochem Behav 1997;58:887-91.
15. Zanoli P, Avallone R, Baraldi M. Behavioral characterisation of the flavonoids apigenin and chrysin. Fitoterapia 2000;71:S117-S23.
16. Wolfman C, Viola H, Paladini A, et al. Possible anxiolytic effects of chrysin, a central benzodiazepine receptor ligand isolated from Passiflora coerulea. Pharmacol Biochem Behav 1994;47:1-4.
17. Galijatovic A, Walle UK, Walle T. Induction of UDP-glucuronosyltransferase by the flavonoids chrysin and quercetin in Caco-2 cells. Pharm Res 2000;17:21-6.

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