Journal Title (Medline/Pubmed accepted abbreviation): Appl Physiol Nutr Metab
doi (if applicable):
Hypothesis/Background: Quercitin, a flavonoid, has been shown in some animal studies to affect adipogenesis and basal metabolism. The authors stated that quercitin may act via a pathway similar to that previously described for epigallocatechin gallate (EGCG). This pathway involves the inhibition of catechol-O-methyltransferase that subsequently causes increased norepinephrine expression and greater sympathetic nervous system activity. The authors therefore hypothesized that quercitin supplementation, combined with vitamin C and niacin to improve its bioavailability, would decrease body mass and increase fat loss in humans.
Subjects: 941 male and female non-institutionalized subjects, 18-85 y. Subjects were stratified by sex (~40% male, 60% female, age (40% young adult, 18-40 y; 40% middle-aged, 41-65 y; and elderly, 61-85 y), and body mass index (BMI) (45% normal, or BMI = 18.5-24.9 kg/m2; 30% overweight, or BMI = 25-29.9 kg/m2; and 25% obese, or BMI>30 kg/m2). Both healthy subjects and those with chronic disease were included-only pregnant or lactating subjects were excluded. Subjects avoided other dietary supplements while on quercitin supplementation, but no other restrictions were placed on diet supplement usage, or medications.
Experimental design: Randomized, double-blind, placebo-controlled
Treatments:There were 3 treatment groups: 1) 500 mg quercitin/day; 2) 1000 mg quercitin/day; and 3) placebo. The subjects received the quercitin in the form of chews (4 per day) with 125 or 250 mg quercitin, 125 or 250 mg vitamin C, and 20 kcal sugar per chew. The placebo chews contained only the sugar.
Protocol:Subjects were randomly assigned to one of the 3 groups and took the 4 chews per day according to the following schedule: 2 chews were ingested each day upon awakening and the other 2 were taken between 1400 hours and the last meal of the day). The period of supplementation was 12 weeks. Body mass and body composition (via bioelectric impedance) were measured before and after the period of supplementation.
This study showed no apparent effects of quercitin supplementation on body mass or composition within a large cohort of subjects. The study had a large sample size and may be representative of how many people in the general population might use a quercitin supplement (e.g., adding it to normal diet and physical activity level). However, it is not known if use of a quercitin supplement in conjunction with a structured diet and exercise program for weight loss would provide additional benefits in that type of scenario. One concern with the study is that the presentation of data on plasma quercitin could have been improved. It was not clear how subjects in the placebo group differed from quercitin treatment and it was also not clear if the influence of quercitin supplementation on plasma quercitin was dose related (or influenced by the vitamin C and niacin). Finally, the presence of both niacin and vitamin C along with quercitin might have somehow obscured any effect that quercitin might have had, but such an effect could not be evaluation because there was no quercitin-only arm in the study.