One of the most abundant of the flavonoid class of polyphenols, quercetin is present in a wide range of dietary sources, such as berries, apples, onions, broccoli, kale, grapes and tea. Its antioxidant and anti-inflammatory properties have long been recognized as a benefit to longevity. The flavonoid has recently been shown to down-regulate the actions of mTOR (mammalian target of rapamycin), an enzyme encoded by the mTOR gene that is responsible for controlling cellular growth, proliferation, protein synthesis, nuclear transcription, and autophagy.26;27 Quercetin has also been shown to activate sirtuin (SIRT 1), a protein encoded by the silent information regulator gene, to influence cell survival, stress resistance, inflammation, immune function, and mitochondrial biogenesis.28;29
Dietary intake of quercetin ranges from 5-40 mg/day but can reach as high as 200-500 mg/day when consumption of fresh fruits is high, particularly when the peel is consumed.30 The median intake of quercetin in the western diet is estimated at 10 mg/day.31 A recent population-based study in Japan calculated the median intake of quercetin at 15.5 mg/day.32 A Swedish population-based study found that individuals with the highest intakes of quercetin (>12 mg/day) experienced a 43% reduction in the risk of stomach cancer when compared to those with the lowest levels of intake (<4 mg/day). Although in the 1970s quercetin was reported as mutagenic, recent studies indicate that quercetin is protective against genotoxins and is regarded as antimutagenic.33 Reviews on the data related to the potential toxicity effects of quercetin support its safety as a dietary supplement at doses exceeding 100 mg/day.34;35
Considering the above, NutriSearch has established a suggested intake for our Blended Standard of 50 mg/day.
NutriSearch Corporation is a Canadian company specializing in nutrition and health research, focussed primarily on multiple vitamin and mineral supplementation.
Our main product is the NutriSearch Comparative Guide to Nutritional Supplements™, which examines current research on the health benefits of supplementation for prevention of degenerative disease. The guide also includes comparisons of broad-spectrum supplements available in various markets around the world, is available in various regions. The guide for the Americas includes product comparisons from Canada, Colombia, México, and the United States. We also publish a guide for Australia and New Zealand.
NutriSearch is also available as a consultant to nutritional supplement manufacturers wanting to improve their supplements.