Estimating flavonoid intake is a first step toward documenting the protective effects of flavonoids against risk of chronic diseases. Although flavonoids are important dietary sources of antioxidants, insufficient data on the comprehensive food composition of flavonoids have delayed the assessment of dietary intake in a population. We aimed to estimate the dietary flavonoid intake in U.S. adults and its sociodemographic subgroups and to document major dietary sources of flavonoids. We expanded the recently released USDA Flavonoid Database to increase its correspondence with the 24-h dietary recall (DR) of the NHANES 1999-2002. We systematically assigned a particular food code to all foods that were prepared or processed similarly. This expanded database included 87% of fruits and fruit juices, 86% of vegetables, 75% of legumes, and, overall, 45% of all foods reported by the 24-h DR of the NHANES 1999-2002. Estimated mean daily total flavonoid intake, 189.7 mg/d, was mainly from flavan-3-ols (83.5%), followed by flavanones (7.6%), flavonols (6.8%), anthocyanidins (1.6%), flavones (0.8%), and isoflavones (0.6%). The flavonoid density of diets increased with age (P < 0.001) and income (P < 0.05). It was higher in women (P < 0.001), Caucasians (P < 0.001), and vitamin supplement users (P < 0.001) and lower in adults with high levels of nonleisure time physical activity (P < 0.01) compared with their counterparts. The greatest daily mean intake of flavonoids was from the following foods: tea (157 mg), citrus fruit juices (8 mg), wine (4 mg), and citrus fruits (3 mg). The proposed relation between flavonoid intake and the prevention of chronic diseases needs further investigation using the estimates introduced in this study.

The importance of antioxidants in reducing risks of chronic diseases has been well established; however, antioxidant intakes by a free-living population have not yet been estimated adequately. In this study, we aimed to estimate total antioxidant intakes from diets and supplement sources in the U.S. population. The USDA Flavonoid Database, food consumption data, and dietary supplement use data of 8809 U.S. adults aged >/=19 y in NHANES 1999-2000 and 2001-2002 were used in this study. Daily total antioxidant intake was 208 mg vitamin C (46 and 54% from diets and supplements, respectively), 20 mg alpha-tocopherol (36 and 64), 223 mug retinol activity equivalents carotenes (86 and 14), 122 mug selenium (89 and 11), and 210 mg flavonoids (98 and 2). Antioxidant intakes differed among sociodemographic subgroups and lifestyle behaviors. Energy-adjusted dietary antioxidant intakes were higher in women, older adults, Caucasians, nonconsumers of alcohol (only for vitamin C and carotenes), nonsmokers (only for vitamin C, vitamin E, and carotenes), and in those with a higher income and exercise level (except for flavonoids) than in their counterparts (P < 0.05). Consumption of fruits, vegetables, and whole grains may be a good strategy to increase antioxidant intake. The possible association between antioxidant intake and the prevalence of chronic diseases should be investigated further.

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Estimation of total antioxidant intake is the first step to investigate the protective effects of antioxidants on oxidative stress-mediated disease. The present study was designed to develop an algorithm to estimate total antioxidant capacity (TAC) of the US diet. TAC of individual antioxidants and 50 popular antioxidant-rich food items in the US diet were determined by 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) assay and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Theoretical TAC of foods was calculated as the sum of individual antioxidant capacities of compounds. The top 10 TAC food items in the US diet according to standard serving size were blueberry > plum > green tea > strawberry > green tea (decaffeinated) > red wine > grape juice > black tea > cherry > grape. Major contributors to TAC were the total phenolic content (r = 0.952, P < 0.001) and flavonoid content (r = 0.827, P < 0.001) of 50 foods. Theoretical TAC was positively correlated to experimental TAC of 50 foods determined by the ABTS assay (r = 0.833, P < 0.001) and the DPPH assay (r = 0.696, P < 0.001), and to TAC from the USDA database for the oxygen radical absorbance capacity (r = 0.484, P = 0.001, n = 44). The TAC database of the US diet has been established and validated. In future studies, TAC of the US diet can be linked to biomarkers of chronic disease.