Flavonoids are widely found in plants. By now, over 5000 naturally occurring flavonoids have been identified. Quercetin, kaempferol, catechins, and anthocyanidins are the best-known flavonoids.
Black and green tea, blueberries, raspberries, strawberries, apples, oranges, and red grapes are very rich in flavonoids. By the way, flavonoids bear the responsibility for vibrant colours of the foods we eat (from the Latin word flavus meaning yellow). This nutrient group is most famous for its antioxidant and anti-inflammatory health benefits. Antioxidants protect body’s cells from damages caused by environmental pollutants, smoking, taking medications or just naturally as we age.
Though there is ongoing research into the potential health benefits of flavonoids, the scientific information is incomplete and sometimes controversial. Maybe that’s why no flavonoids have been approved as pharmaceutical drugs and no health claim for flavonoids have been made.
1. Results of in vitro research
In vitro studies are performed with biological molecules in test-tubes, flasks, petri dishes etc., outside their normal biological context. In contrast, in vivo studies are those conducted in animals including humans, and whole plants. So, in vitro flavonoids demonstrated a wide range of biological and pharmacological activities such as: anti-allergic, anti-inflammatory, antioxidant, anti-microbial, anti-cancer, and anti-diarrheal activities.
2. Antioxidant effect
It’s still unclear whether flavonoids have antioxidant properties or not due to the fact that they are poorly absorbed in the human body (less than 5%) and quickly metabolized and excreted. More likely, the increase in antioxidant capacity of blood seen after eating flavonoid-rich foods occurs indirectly due to production of uric acid resulting from flavonoid depolymerization.
3. Anti-inflammation effect
It is suggested that flavonoids may have anti-inflammatory properties due to their ability to inhibit reactive oxygen or nitrogen compounds.
4. Cancer prevention qualities
Conflicting results have been obtained in clinical studies researching the relationship between flavonoid intake and cancer prevention. Apparently, there are two exceptions – gastric carcinoma and smoking-related cancers, where direct correlation between dietary flavonoid consumption and cancer was found*.
5. Cardiovascular diseases
This type of scientific and clinical research is the most intensive. Studies on the dietary effects of plant flavonoids on cardiovascular diseases suggest that flavonoids: reduce oxidative stress, arterial blood pressure and risk of atherosclerosis; inhibit thrombus formation; regulate carbohydrate and glucose metabolism and demonstrate some other health benefits
6. Antibacterial effects
In numerous in vitro and limited in vivo studies it has been shown that flavonoids have direct antibacterial and synergistic with antibiotics activities.