This is the key message in a risk assessment requested by the Norwegian Food Safety Authority.

In the report, it is concluded that it is safe to use quercetin or rutin in food supplements in daily doses of 5 mg rutin for children from four years of age, doses of

25 mg rutin for adults and 500 mg quercetin dihydrate for adults for at least three months.

Methods

VKM has evaluated the risk of adverse health effects from daily intake of food supplements with 25 mg rutin or 500 mg quercetin dihydrate for adults from 18 years of age and older, and with 5 mg rutin for children from four years of age.

Quercetin and rutin are flavonoids. These substances occur naturally in plants and are present in food, especially in fruit, vegetables and tea. Many flavonoids in food and beverages have low absorption in the body.

This risk assessment is based on information from a systematic review of 23 randomised controlled studies (i.e. studies evaluating the effects of a treatment by randomising the participants to treatment and control group(s)). These studies were performed on adults. In addition, information about how these substances are handled by the body and some experimental animal studies were used in this evaluation.

The studies had examined, but observed few adverse health effects, all of low severity. The study with the longest duration exposed the participants for 10 months.

Lack of data

The conclusion for children is based on the studies on adults and one study specifically on children. Because of the insufficient data on effects on pregnant women and their fetuses, and lack of data on breast-feeding women and their infants, as well as on children in general, is it not known whether these groups potentially could be more vulnerable for the effects of these substances than adults in general.

The human studies examined mainly positive (beneficial) effects of quercetin and rutin on various health conditions and diseases. Potentially adverse health effects or events were documented and examined with varying thoroughness and very few adverse effects, all with low severity, were observed. These results was supported by the experimental animal studies.

"Since most of the included studies on quercetin and rutin did not examine the effects when used in more than three months, the effects of longer exposure is more uncertain, although a few studies did not observed adverse effects after exposure for six to ten months," says Inger-Lise Steffensen, scientific leader for the project group.

VKM has not estimated contributions from other sources of quercetin or rutin such as from food, nor has VKM assessed the use of these substances for the treatment of various conditions and diseases.

Some data may suggest that people with chronic kidney disease or estrogen-dependent cancer may be vulnerable to harmful effects of quercetin.

Studies in humans and animals have shown that quercetin can affect the absorption of various drugs in the body and can affect enzymes that convert drugs.

About quercetin and rutin

Quercetin and rutin are included in the group "other substances". These are substances with a nutritional or physiological effect, and which are not vitamins or minerals.

The risk assessment is approved by VKM's Scientific Panel on nutrition, dietetic products, novel food and allergies.