Blood levels of quercetin were five times higher after consuming a quercetin-enriched cereal bars than consuming quercetin powder-filled hard capsules, according to findings published in the British Journal of Nutrition.
“If the intake of quercetin and related flavonols can indeed be proven to reduce the risk of CVD, then the production of foods with a more highly bioavailable form of quercetin might become a realistic proposition,” wrote the researchers, led by Sarah Egert from the University of Bonn.
“Modification of intestinal absorption by food factors may be a promising technique to control the physiological function and effectiveness of quercetin.”
The study is said to be the first to compare bioavailability of the flavonol from cereal bars with quercetin capsules.
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).
According to the German researchers behind the new study, in order for quercetin to provide potential health benefits it must be bioavailable and the delivery method could play a role. In order to test this they formulated cereal bars and capsules with quercetin derived from onion skin extract at a dose of 130 milligrams.
“We used this moderate supranutritional but non-pharmacological dose of quercetin, since our data should provide a rational basis for the development of functional foods,” they explained.
The pilot study involved six healthy women aged between 22 and 28 and randomly assigned them to receive either quercetin-enriched cereal bars or quercetin powder-filled hard capsules in a cross-over design trial.
Results showed that bioavailability was five times higher from the cereal bars compared to the capsules, while there were no differences in the time needed for blood levels of quercetin to peak from both delivery formats.
Blood levels of the quercetin metabolites, isorhamnetin and tamarixetin, were also four and nine times higher after ingestion of quercetin by quercetin-enriched cereal bars than after ingestion of the capsules, said the researchers.
Commenting the difference between the groups, Egert and her co-workers note that the quercetin in the bars was formulated as a solid dispersion, whereas the capsules were formulated using a powder.
“Intimate mixing of quercetin with the components (solid macroparticles) of the cereal bar resulted in a homogenous distribution of quercetin,” they said. “The addition of a viscous binding matrix (glucose–fructose syrup and soft sugar) converted the whole mixture after cooling into a solid dispersion.
“Solid dispersions provide a large surface for compounds with low solubility and are utilised for pharmaceuticals to enhance bioavailability.”
Source: British Journal of Nutrition
Volume 107, Issue 04, pp 539-546, doi: 10.1017/S0007114511003242
“Enriched cereal bars are more effective in increasing plasma quercetin compared with quercetin from powder-filled hard capsules”
Authors: S. Egert, S. Wolffram, B. Schulze, P. Langguth, et al.