polyphenols tea antioxidant black tea oxidative stress blood pressure caffeine flavonoid homocysteine isoprostanes lipid peroxidation Nutritional epidemiology-research communication biomarkers bone mineral density carbohydrates cardiovascular disease risk cardiovascular risk catechol-O-methyltransferase chocolate cholesterol endothelial function flavonoids folate fracture risk genistein green tea human nutrition and metabolism humans isoflavonoids lean red lipid lipoprotein lipoproteins metabolism and metabolic studies minerals and phytochemicals nutrition and disease nutritional epidemiology and public health phenolic acids phytoestrogens platelet aggregation platelet function polyphenolic compounds postprandial red meat tea coffee total homocysteine vitamins women