Researchers from the Appalachian State University in North Carolina report that a combination of quercetin, vitamin C, and niacin was safe, but had no effect on markers of inflammation.
Quercetin is an antioxidant flavonoid found in fruits and vegetables. Potential health benefits include lowering of inflammatory markers, cholesterol reduction, and improving blood pressure.
However, many of these potential benefits are the result of in vitro or animal studies and data from human studies is rare.
One such human study by researchers from the University of Utah did indicate that a daily 730 milligram supplement of quercetin led to significant reductions in blood pressure.
The study, said to be the first to report the blood pressure-lowering activity of this flavonol, was published in the Journal of Nutrition (Nov. 2007, Vol. 137, pp. 2405-2411).
Data from the new randomized controlled trial muddies the water further, with no potential changes in various disease risk markers reported after supplementing for 12 weeks with either 500 or 1,000 milligrams of the flavonoid.
“A large apple provides 8 to 10 mg quercetin; thus, the supplement levels used in this study are not attainable through the diet alone,” wrote the researchers in the Journal of the American Dietetic Association.
“The lack of effect of long-term quercetin-vitamin C-niacin supplementation on the disease risk factors measured in this study is in agreement with the findings reported by other investigators.
“Future research will determine if the bioactive effects of quercetin measured in vitro can be replicated in humans by adding other synergistic food components such as isoquercetin, green tea extract, fish oil, antioxidants, and other types of polyphenols.”
The North Carolina-based scientists recruited 1,002 people aged between 18 and 85 to participate in their study. The mean age of the participants was 45, and the mean BMI was 27 kg/m2.
Participants were randomly assigned to one of three groups: One group received placebo, the second group received a supplement providing a daily dose of 500 mg quercetin, 125 mg vitamin C, and 5 mg niacin. The third group received double the doses in the second group’s supplements.
According to the researchers, vitamin C and niacin may enhance the bioavailability of quercetin.
After 12 weeks no changed in markers of inflammation were observed between any of the groups.
The researchers did report a slight decrease in blood pressure was recorded in the both quercetin groups, compared to placebo.
Source: Journal of the American Dietetic Association
Volume 111, Issue 4, Pages 542-549
“Influence of Quercetin Supplementation on Disease Risk Factors in Community-Dwelling Adults”
Authors: A.M. Knab, R.A. Shanely, D.A. Henson, F. Jin, S.A. Heinz, M.D. Austin, D.C. Nieman