Consumption of nuts such as almonds has been linked to a reduced risk of coronary heart diseases. The
almond skins are very rich in phytochemicals, mainly flavonoids and it is believed that they are responsible for the health benefits. Sang et al identified many phytochemicals in almond skin, including catechins, flavonols, flavones as aglycones and glycosides (Antioxidative phenolics compounds isolated from almond skin. J. Agric. Food Chem. 50:2459-2463, 2002). Flavonoids are known to have antioxidant, vasodilatory and anti-inflammatory activity. Jenkins at al have shown in their study that almond consumption can reduce LDL cholesterol and reduce LDL oxidation. (Dose response of almonds on coronary heart disease risk factors: blood lipids, oxidized low-density lipoproteins, lipoprotein, homocysteine, and pulmonary nitric oxide. Circulation 106: 1327-1332, 2002) However, it is unknown if these flavonoids are bioavailable. The purpose of this study determine the bioavailability of flavonoids in almond skins and to see if the flavonoids act synergistically with the antioxidants ascorbic acid and vitamin E. The tests were carried out on an alcohol extract of almond skin, which was rich in catechins and flavonols. Previous studies on the bioavailability or bioactivity of flavonoids have been carried out on single flavonoids. This is the first experiment that uses a complex mixture of different flavonoids.
The bioactivity of the almond skin extract was determined in vitro by measuring human LDL oxidation. The researchers found that almond skin extract increased resistance to LDL oxidation in a dose dependent manner. The in vitro addition of vitamin E and ascorbic acid synergistically reduced LDL oxidation.
The bioavailability was tested in vivo with hamster by measuring blood levels of catechin, epicatechin,
quercetin,
kaempferol and isorhamnetin. These phytochemicals reach peak plasma levels after between 1 and 3 hours. The level of isorhamnetin in the liver was significantly increased. The almond skin extract reduced the oxidation of LDL by 18 percent.
The study concluded that almond skin extract possesses antioxidant activity in vitro. Almond skin extract is bioavailable and acts synergistically with ascorbic acid and vitamin E to prevent LDL oxidation. More research is needed to investigate the relationship between flavanoids and natural vitamine E of almonds and their effect on cardiovascular disease.
Source: Chung-Yen Chen, Paul E. Milbury, Karen Lapsley and Jeffrey B. Blumberg. Flavonoids from Almond Skins Are Bioavailable and Act Synergistically with Vitamins C and E to Enhance Hamster and Human LDL Resistance to Oxidation. J. Nutr. 135:1366-1373, June 2005