(resveratrol), which also include supporting evidence from animal models of TBI. All studies included in these tables are from 1990 and after. The occurrence or absence of adverse effects in humans is included if reported by the authors.
Flavonoids are the group of polyphenols most studied. Their structure consists of two aromatic rings bound together by three carbons that form an oxygenated heterocycle. More than 4,000 flavonoids have been identified and categorized into seven subclasses, based on their structure: flavonols (e.g., quercetin), flavones (e.g., apigenin), flavanones (e.g., hesperetin), flavan-3-ols (e.g., epicatechin), anthocyanins (e.g., cyanidin), polymers (e.g., proanthocyanidins), and isoflavones (e.g., genistein). In addition to their antioxidant capacity, flavonoids can also alleviate neuroinflammation and regulate mitochondrial function and neuronal cell signaling cascades (Ramassamy, 2006; Spencer, 2008; Vafeiadou et al., 2007). Because of these properties and their ability to pass through the blood-brain barrier (BBB) (Dreiseitel et al., 2009; Youdim et al., 2004), flavonoids have been suggested as potential neuroprotective agents. Below is an overview of selected human trials that summarizes the evidence on flavonoid use for the prevention of cardiovascular diseases, a group of diseases that share some common pathways (e.g., oxidative stress and inflammation) with TBI (see Table 14-1 for both human and animal studies from 1990 and later). The results from animal studies on flavonoids and TBI are also presented. The committee highlights curcumin as one flavonoid for which there is substantial evidence of neuroprotectant effects in animal models of TBI.
In light of the work of Miller and colleagues (2005), any trials undertaken should ensure that dose levels of flavonoids do not approach levels that might cause adverse events, such as higher risk of mortality.
Hollman and colleagues reviewed six prospective observational studies (n = 111,067) addressing the effects of dietary intake of flavonol on stroke risk (Hollman et al., 2010). In this review, the pooled RR of stroke, for the highest versus the lowest intake of flavonol, was 0.80. In a sample of 9,208 Finnish men and women, apple consumption was significantly associated with a reduced risk of developing thrombotic stroke during a 28-year follow-up period (Knekt et al., 2000). However, the authors failed to find any significant association between quercetin and stroke (Knekt et al., 2000). Consumption of tea, as well as catechin, was not associated with significantly lower risks of stroke in the Zutphen Elderly study (806 men aged 65–84 years at baseline) in the Netherlands (Arts et al., 2001), or the College Alumni Health Study in Japan (17,228 participants with a mean age of 59.5 years at baseline) (Sesso et al., 2003b). The Women’s Health study, a large, randomized, clinical control trial that looked at vitamin E and cardiovascular disease, examined the association of food intakes of flavonols and flavones and primary food sources of flavonoids with cardiovascular disease (Sesso et al., 2003a). The study found no clear association with stroke. The authors observed nonsignificant inverse associations of the consumption of broccoli, apples, and tea with important vascular events. It is, however, noteworthy that estimation of total flavonoid intake in this study was based on an obsolete food composition table, which included only two flavonoid subclasses (flavonols and flavones). The potential neuroprotective effects of