Metastudy confirms quercetin's antiviral potential against Covid-19
In case of Covid-19, a daily dose of at least 600 milligrams of quercetin may reduce the risk of admission to hospital, the need for ICU treatment and death. This is suggested by a meta-analysis published in Food Science & Nutrition.
Researchers from Kermanshah University of Medical Sciences in Iran traced 5 previously published trials in which a total of 544 subjects with a not too serious form of Covid-19 served as test subjects.
All trials were double-blind and randomized. The subjects in the groups receiving quercetin were given the flavonoid in doses of 500-1500 milligrams per day for 1-4 weeks.
The trials date from 2021-2023. The methodology of the trials was not perfect. There was something to note about the design of each trial, as shown in the table below. Click on it for a larger version.
Supplementation with 600-1000 milligrams per day of quercetin reduced the chance that the subjects had to be admitted to hospital by 70 percent, the chance of a stay in the ICU by 73 percent and the chance of death by 82 percent.
In the trials, quercetin inhibited the increase in the enzyme LDH in the blood of the test subjects. This suggests that the virus caused less damage at the cellular level.
As with MERS and SARS, the virus can cause a severe immune reaction that causes more damage, especially in the lungs, than the body can handle. In addition, the immune reaction activates the formation of blood clots. The researchers suspect that quercetin dampens these immune responses.
Quercetin probably frustrates the entry of the SARS-CoV-2 virus into cells via the ACE-2 receptor. At the same time, quercetin inhibits viral enzymes such as 3CLPro and RNA-dependent RNA polymerase (RdRp). Because the virus needs these enzymes to replicate in cells, quercetin gives the immune system more opportunity to deal with the virus.
"The findings from this systematic review and meta-analysis demonstrate its potential as a therapeutic agent against Covid-19", summarize the Iranians. "Due to the low certainty of evidence, these results should be interpreted with caution."
Food Sci Nutr. 2023 Sep 26;11(12):7504-14.
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