QUERCETIN: WHAT IS IT?
Quercetin is a flavonoid found naturally in a wide variety of fruits and vegetables.
Chemically, most flavonoids consist of a central skeleton composed of 15 carbon atoms and, specifically, 3 rings, 2 of which are benzyl and 1 heterocyclic.
QUERCETIN IN FOOD
Quercetin is a ubiquitous flavonoid. The foods containing the most quercetin are:
| Food | Quantity of Quercetin mg/100 g |
| Capers | 234 |
| Dill | 79,0 |
| Fennel leaves | 46,8 |
| Oregano | 42,0 |
| Chilli | 32,6 |
| Spinach | 27,2 |
| Cabbage | 22,6 |
| Cherry | 17,4 |
| Lettuce | 14,7 |
| Asparagus | 14,0-23,6 |
| Romaine lettuce | 12,0 |
| Onions | 11-45,0 |
| Chives | 10,4 |
| Red lettuce | 10,3-30,6 |
| Green pepper | 9,9 |
| Wild leeks | 8,36 |
| Apples | 4,01 |
| Fuji Apples | 2,3 |
| Tomatoes | 1,6-3,3 |
| Leeks | 0,9 |
| Broccoli | 0,5-13,7 |
QUERCETIN IN MEDICINAL PLANTS
Good levels of quercetin can also be found in some medicinal plants such as:
- Hypericum
- Horse chestnut
- Ginkgo Biloba
- Sophora Japonica (Also known as Acacia of Japan, from which a particularly pure extract is obtained from the inflorescence).
THE RECOMMENDED DAILY DOSE OF QUERCETIN
The recommended intake is around 500 mg per day; however, with a Western-style diet, a daily intake of around 30 mg is possible.
THE ROLE OF QUERCETIN
Quercetin has several important functions:
- Antioxidant: reduces the formation of free radicals.
- Anti-inflammatory–anti-allergic: inhibits histamine release, as it reduces mast cell inflammation.
- Immunomodulatory: decreases pro-inflammatory cytokines.
- Antiviral: transports zinc into cells, where it acts by preventing virus replication.
- Immunomodulatory-antioxidant: possesses anti-cancer potential, as it reduces the risk of cell alterations.
In addition, this flavonoid has a synergistic action with vitamin C, which increases its bioavailability, resulting in an anti-inflammatory-antioxidant action.
QUERCETIN SUPPLEMENTS
Although there are foods rich in quercetin, as is illustrated in the table above, the use of food supplements containing this flavonoid is recommended, due to both the low proportion provided by the foods themselves and its poor bioavailability.
Indeed, precisely because of quercetin’s poor bioavailability and thus its poor absorption in the intestines, it is very common to find food supplements containing, in addition to quercetin, vitamin C, which increases its bioavailability.
In healthy adults, at the recommended daily dose, preferably taken with meals, quercetin is safe and well tolerated.
