The cardioprotective properties of quercetin, demonstrated in animal and in vitro studies, provide a theoretical basis for the use of quercetin in the prevention of cardiovascular disease; however, current human data is less encouraging.
A double-blind, placebo-controlled study investigating the effects of a quercetin-containing supplement on plasma quercetin status, risk factors for heart disease and serum/platelet fatty acid levels was conducted on 27 healthy men and women with cholesterol levels of 4.0-7.2 mmol/L (Conquer et al 1998). The subjects consumed a quercetin-containing supplement (1 g quercetin/day) or rice flour placebo for 28 days. Quercetin intakes were approximately 50-fold greater than dietary intakes previously associated with lower coronary heart disease mortality in epidemiologic studies. Plasma quercetin concentrations were approximately 23-fold greater in subjects consuming the quercetin capsules than in the placebo group. Quercetin supplementation did not alter serum total, LDL- or HDL-cholesterol or triglyceride levels, or other cardiovascular disease or thrombogenic risk factors such as platelet thromboxane B2 production, blood pressure or resting heart rate. This is in contrast to a previous trial (Hubbard et al 2004), which demonstrated inhibition of platelet aggregation and signalling and thrombus formation at doses of 150 mg or 300 mg quercetin-4'-0-beta-D-glucoside, were not reproduced using the dose and form in this study. There was also no effect on the levels of omega-3 or omega-6 polyunsaturated fatty acids in serum or platelet phospholipids (Conquer et al 1998). Further investigation with larger and longer term trials is required to determine the effects and safety of quercetin in the prevention of cardiovascular disease in humans.
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