Healthy men who took quercetin supplements for eight weeks displayed a significant 4.5% increase in levels of HDL (good) cholesterol and decreased systolic blood pressure by an average of 5.7 mmHg, according to findings published in Nutrition, Metabolism and Cardiovascular Diseases.
Researchers from the Federal Research Institute of Nutrition and Food in Germany report that benefits to waist circumference were linked to genotype of the individual, however, with men with the APOE3 genotype displaying a shrinking waist, while no effect was recorded in men with an APOE4 genotype.
Apolipoprotein E (APOE ) is said to play a key role in the metabolism of plasma lipids and has influences the development of atherosclerosis. People with the E4 allele are said to be at higher coronary risk.
“Our data, however, provide evidence of moderate beneficial effects on blood pressure and lipidemia, and show for the first time that the postprandial state may emphasize quercetin effects that are less clear under fasting conditions,” wrote the researchers, led by Maria Pfeuffer.
“There were genotype-dependent effects on BMI and waist circumference which could not be explained by anti-inflammatory actions of quercetin.”
On the flip side, a slight increase in levels of the pro-inflammatory compound TNF-alpha was recorded by the researchers.
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).
The new study adds to this, and provides an insight into how our genes may affect our response to nutrients.
Pfeuffer and her co-workers recruited 49 healthy men. The men had either two E3 alleles, two E4 alleles, or a mixture of the two (we inherit one allele – or form of the gene – from our mother and one from our father).
The men were randomly assigned to receive either daily quercetin supplements (150 milligrams per day) or placebo for eight weeks, A three-week washout period followed this, and then the men were crossed over to the other group.
Results showed that, after a fat-rich meal, the quercetin reduced blood levels of triacylglycerol and boosted HDL levels.
“Quercetin moderately but significantly reduced BMI, body weight and waist circumference in APOE3/3 but not in APOE4 subjects,” wrote the researchers. “No such effects have been reported before in humans.”
Source: Nutrition, Metabolism and Cardiovascular Diseases
Published online ahead of print, doi: 10.1016/j.numecd.2011.08.010
“Effect of quercetin on traits of the metabolic syndrome, endothelial function and inflammatory parameters in men with different APOE isoforms”
Authors: M. Pfeuffer, A. Auinger, U. Bley, I. Kraus-Stojanowic, C. Laue, P. Winkler, C.E. Rüfer, J. Frank, C. Bösch-Saadatmandi, G. Rimbach, J. Schrezenmeir