From the March 1997 Issue of Nutrition Science News
Along with synthetic protease inhibitors, drug companies are using synthetic reverse transcriptase inhibitor drugs to combat AIDS. On one hand, the possibility exists that natural protease inhibitors could help combat HIV the same way they help to prevent cancer; by the same token, it is possible that natural reverse transcriptase inhibitors could do the same.
A potent natural reverse transcriptase blocker is quercetin, a bioflavonoid commonly found in red apples and red onions and also available as a food supplement. Though large doses may be required in humans to produce therapeutic effects, quercetin has been shown to have antiviral activity against HIV, herpes simplex, polio-virus and the respiratory syncytial virus.  One study even showed that it was possible to overcome the polio virus by pairing vitamin C with quercetin. 
Quercetin has also been shown to significantly inhibit oral tumors in hamsters when tested by fluorescence spectroscopy. Cancerous or precancerous cells exhibit greater fluorescence when exposed to light. Quercetin-treated tissues exhibited much less fluorescence than untreated tissues. 
Most important, quercetin was found to be the most potent reverse transcriptase inhibitor compared to three other flavonoids (myricetin, quercetagetin and baicalein), even at concentrations as low as 2 mcg/mL.  And, despite reports to the contrary, recent studies have dispelled previous concerns over possible mutagenicity and poor absorption of quercetin. [5, 6]
Kaul, T.N., Middleton E., & Ogra P.L.
Antiviral effects of flavonoids on human viruses
J Med Virol, 15: 71-79, 1985
Vrijsen, R., Everaert, L., & Boeye A.
Antiviral activity of flavones and potentiation by ascorbate
J Gen Virol 69: 1749-51, 1988
Balasubramanian, S., & Govindasamy, S.
Inhibitory effects of dietary flavonol quercetin on 7,12-dimethyl-benz[a]anthracene-induced hamster buccal pouch carcinogenesis
Carcinogenesis 17: 877-79, 1996
Ono, K., Nakane, H., et al.
Differential inhibitory effects of various flavonoids on the activities of reverse transcriptase and cellular DNA and RNA polymerases
Eur J Biochem, 190: 469-76, 1990
Calomme, M., & Pieters, L.
Inhibition of bacterial mutagenesis by citrus flavonoids
Planta Medica 62: 222-26, 1996
Hollman, P.C.H., de Vries, J., et al.
Absorption of dietary quercetin glycosides and quercetin in healthy ileostomy volunteers
Am J Clin Nut 62: 1276-82, 1995
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