Vitamin E is an essential nutrient, that protects cells from oxidative stress, and which cannot be made by the body. Oxidative stress results from the overproduction of free radicals, which cause oxidative damage to cells, and con-tributes to the development of chronic dis-ease. The term vitamin E refers to a family of eight closely related compounds: four tocotrienols (alpha-, beta-, delta-, and gamma-tocotrienol) and four tocopherols (alpha-, beta-, delta-, and gamma-tocopherol). Figure 1 shows the molecular structures for tocotrienol and tocopherol, which are quite similar in that they both consist of a chromanol ring and a phytyl side chain. The
Epicatechin is a flavanol with anti-oxidant properties that is found in cocoa (Theobroma cacao), green tea (Camellia sinensis), and grapes. This naturally occurring flavanol is the most abundant bioactive compound in cocoa, constituting approximately 35% of the total polyphenol content (120–180 g/kg) (1). Epidemiological (2) and clinical studies (3–8) have investigated the effects of cocoa and epicatechin supplementation on cardiovascular and metabolic health. Table 1 summarizes the potential health benefits of epicatechin supplementation.
An epidemiological human study has investigated the effect of high consumption of cocoa on the cardiovascular heath of a population of Kuna Indians (2). These indigenous peoples were native to a remote island near the coast of Panama (Ailigandi), and were found to consume high daily levels of cocoa. The study found that Ailigandi-dwelling Kuna Indians had relatively low blood pressure levels and a lower incidence of cardiovascular disease, compared to Kuna Indians who migrated to a suburb of Panama City (Vera Cruz). The reason for the low blood pressure levels and lower incidence of cardiovascular disease was attributed to higher daily levels of cocoa consumption (10-fold higher), compared to the Kuna Indians who migrated to Vera Cruz. The potential role for cocoa flavanols in contributing to cardiovascular health was investigated in a randomized, double-blind, placebo-controlled human clinical study (3). The study found that oral administration of 46 g high-flavanol dark chocolate (containing 46 mg epicatechin) increased blood epicatechin levels and improved endothelial function. Endothelial function was assessed using a technique called flow-mediated dilation (FMD), which measured the natural dilation (widening) of a blood vessel (in this case the brachial artery) in response to an increase in blood flow. Participants administered high-flavanol dark chocolate had an improved FMD response compared to a placebo group administered low-flavanol dark chocolate.
The potential effects of pure epicatechin supplementation on cardiovascular health have been investigated in human subjects over the past decade. In 2006, a proof-of-concept, single-blind, placebo-controlled human study assessed the effects of epicatechin supplementation on FMD response and peripheral arterial tonometry (PAT) (4). In contrast to FMD, which uses high-resolution ultrasound, PAT involves the use of fingertip plethysmography to measure endothelial function.
Six healthy participants aged 25 to 32 were administered 1 mg/kg or 2 mg/kg epicatechin dissolved in water (4). A placebo group was administered 3 ml/kg water alone. The study found that FMD and PAT responses were significantly improved two hours after oral ingestion of epicatechin, compared to the placebo group. At the lower dose of 1 mg/kg epicatechin, FMD response was significantly improved over a period of one to two hours after administration and PAT response was significantly improved one to two hours after administration, in comparison to baseline.
Endothelial dysfunction is an imbalance in factors that cause the relaxation (nitric oxide) or contraction (endothelin-1) of the endothelium, the inner lining of blood vessels.
Flow-Mediated Dilation (FMD)
Flow-mediated dilation measures the natural dilation (widening) of a blood vessel in response to an increase in blood flow. An impaired FMD response indicates endothelial dysfunction.
Peripheral Arterial Tonometry (PAT)
Peripheral arterial tonometry uses fingertip plethysmography to measure endothelial function. An impaired PAT response indicates endothelial dysfunction.
Two years later, a randomized, unblinded, placebo-controlled human study assessed the effects of pure epicatechin supplementation on the blood/urine levels of mediators of endothelial function, including S-nitrosothiol, nitrite/nitrate, and endothelin-1 (5). S-nitrosothiol was measured because it acts as the body’s store of nitric oxide (NO), which is a potent vasodilator that directly dilates (widens) blood vessels, reducing blood pressure levels. Nitrite/nitrate are products of NO metabolism. In contrast, endothlin-1 is a potent vasoconstrictor that acts to constrict (narrow) blood vessels, increasing blood pressure levels, and is a biomarker of endothelial dysfunction (9).
During the study (5), healthy male participants were administered 200 mg epicatechin dissolved in 300 ml water. A placebo group was administered 300 ml water alone. Two hours after oral ingestion of 200 mg epicatechin, blood levels of nitrite and S-nitrosothiol were significantly increased, in comparison to the placebo group. Urinary nitrate levels were also significantly increased five hours after oral ingestion of 200 mg epicatechin. In contrast, levels of endothelin-1 in blood were significantly reduced.
The effects of epicatechin supplementation on physiological measures of endothelial function (FMD response and blood levels of NO) and dysfunction (endothelin-1 and sE-selectin), among other parameters, were investigated in a randomized, double-blind, placebo-controlled human study (6, 7). sE-selectin (also known as soluble E-selectin) is a soluble adhesion molecule that, like endothelin-1, is a biomarker of endothelial dysfunction (10). During this study (6, 7), participants were asked to avoid consumption of flavanoid-rich foods (cocoa, tea, apples, onion, and red wine) and consumed a standardized low-flavanol meal the evening before measurements were made. Participants were administered 100 mg epicatechin each day over an intervention period of four weeks. Baseline measurements were collected at the start of each intervention period and the effects of epicatechin were assessed at the end of the four-week intervention period.
The study (6, 7) found that epicatechin supplementation reduced the levels of sE-selectin, in comparison to placebo. However, epicatechin was not found to affect FMD response or blood levels of NO or endothelin-1 after four weeks of supplementation (6). This may appear to be contradictory to results from other studies suggesting that epicatechin supplementation improved FMD response and reduced S-nitrosothiol and endothelin-1 levels two hours after administration (4, 5). The negative results were caused by a lower dose of epicatechin (100 mg per day ), while the dose administered in the studies that reported that epicatechin supplementation improved FMD response and reduced S-nitrosothiol and endothelin-1 levels was higher (up to 2 mg/kg or 200 mg per day [4, 5]).
An open-label human study assessed the effects of epicatechin supplementation on (postprandial) glucose levels and lipid metabolism after consumption of a standardized meal (nutritional supplement) (8). Human participants were subject to oral metabolic tolerance testing (OMTT), which simulates meal ingestion by the administration of a standardized nutritional supplement containing 39 g of carbohydrates, 9 g of protein, and 6 g of lipids (a total of 246 kcal). Between 0–4 hours after meal ingestion, measurements were made of the participants’ respiratory quotient (VCO2/VO2), lipid oxidation levels (%kcal from fat), blood glucose levels, and blood triglyceride levels. One week later this process was repeated, but with the participants first being administered 1 mg/kg epicatechin provided in gelatin capsules 30 min prior to metabolic challenge.
Results from the study (8) suggested that oral supplementation with 1 mg/kg epicatechin prior to meal ingestion significantly reduced the postprandial respiratory quotient in a subgroup of non-overweight participants (with an average BMI of 22.0 kg/m2), in comparison to meal ingestion alone. The respiratory quotient is the ratio of the volume of carbon dioxide eliminated from the body and the volume of oxygen consumed by the body. The value of the respiratory quotient indicates the type of metabolism that predominates after meal ingestion. Reduction in the value of the respiratory quotient suggested a shift in metabolism away from the synthesis of lipid (fat) towards the break-down (oxidation) of lipid for energy. Coinciding with reduced respiratory quotient, estimates of postprandial lipid oxidation were significantly increased. Postprandial lipid oxidation is an estimate of the proportion of energy (%kcal) obtained from lipid after meal ingestion.
S-Nitrosothiol and Nitric Oxide
S-nitrosothiol acts as the body’s store of nitric oxide (NO). NO is a potent vasodilator that directly dilates (widens) blood vessels, reducing blood pressure levels.
Nitrite/nitrate are products of NO metabolism and also act as the body’s store of nitric oxide.
Endothlin-1 is a potent vasocon-strictor that acts to constrict (narrow) blood vessels, increasing blood pressure levels.
E-selectin (also known as soluble E-selectin) is a soluble adhesion molecule and a biomarker of endothelial dys-function.
Postprandial Lipid Oxidation
Lipid oxidation is an estimate of the percentage of calories (%kcal) released from lipid (fat) oxidation. Postprandial lipid oxidation is the amount of energy released from the break-down of fat after meal ingestion.
In a subgroup of overweight participants (average BMI of 27.1 kg/m2), oral supplementation with epicatechin prior to meal ingestion also significantly reduced postprandial respiratory quotient. In this subgroup, postprandial lipid oxidation was also significantly increased. In a different subgroup of participants with high levels of adipose (fat) tissue, oral supplementation with epicatechin prior to meal ingestion significantly increased postprandial lipid oxidation, but reduced blood glucose levels and reduced blood triglyceride levels.
The effects of epicatechin supplementation on physiological measures of glucose metabolism/insulin resistance (blood levels of glucose and insulin, and HOMA-IR score), among other parameters, were investigated in a randomized, double-blind, placebo-controlled human study (6, 7). Insulin is the hormone that acts to enable cells to obtain the energy they need from glucose in the blood. HOMA-IR (homeostatic model assessment-insulin resistance) is a method of assessing insulin resistance using blood glucose and insulin levels.
The study (6) found that epicatechin supplementation reduced the levels of biomarkers of insulin resistance (blood insulin and HOMA-IR), in comparison to placebo. However, epicatechin was not found to affect fasting blood glucose levels after four-weeks supplementation. This may appear contradictory to results from another study that suggested that epicatechin supplementation reduced postprandial blood glucose levels up to two hours after administration (8). However, this apparent discrepancy may have suggested that epicatechin supplementation may have reduced postprandial blood glucose levels only without affecting fasting glucose levels – a potentially beneficial property.
Collectively, studies have suggested that high-flavanol cocoa contributed to improved endothelial function, as evidenced by improvements in FMD response. Pure epicatechin supplementation improved endothelial function and reduced the levels of biomarkers of endothelial dysfunction. Studies also suggested that epicatechin supplementation contributed to the break-down of lipid after meal ingestion. In addition, epicatechin reduced postprandial blood glucose and triglyceride levels and reduced insulin resistance (blood insulin levels and HOMA-IR score). The exact molecular mechanism of action of epicatechin is not completely understood. Nevertheless, epicatechin has shown potential as a natural supplement for the support of cardiovascular and metabolic health.
Postprandial Respiratory Quotient The respiratory quotient is the ratio of the volume of carbon dioxide eliminated from the body and the volume of oxygen consumed by the body (VCO2/VO2). The value of the respiratory quotient indicates the type of metabolism that dominates, i.e. fat synthesis (>1.05), carbohydrate oxidation (0.95–1.05), mixed carbohydrate/lipid oxidation (0.85–1.0), or lipid oxidation (0.65–0.85). A reduction in the value of the respiratory quotient suggests a shift in metabolism towards to the breakdown of lipids (fats). The postprandial respiratory quotient is a measure of the nature of metabolism after meal ingestion.
Postprandial HOMA-IR Score HOMA-IR (homeostatic model assessment-insulin resistance) is a method of assessing insulin resistance using blood levels of glucose and insulin. A postprandial HOMA-IR score is a measure of insulin resistance after meal ingestion.
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