For a long time we’ve heard that green tea does this and green tea does that and green tea has this and that benefit, while poor old black tea sits in the cupboard waiting for its chance on the stage. There’s little question that green tea and its army of polyphenols have distinct nutritional value. It promises to reduce the risk of cardiovascular disease, kidney stones, tooth decay and cancer, while it improves bone density and cognitive function. Now we know that black tea has its own virtues.
Tea doesn’t start out being black. It’s just more oxidized than the others, and that gives it a stronger taste. Green tea will lose its flavor in a year, but black will endure. Like most leafy plants, tea leaves start to wilt and oxidize soon after being picked, and then darken as the chlorophyll breaks down and tannins are released. The enzymes that cause the darkening are interrupted by heating the leaves at the appropriate time, controlling moisture to prevent mold from growing. The tannins that give tea its astringency are not peculiar to that plant, but appear in a wide variety of flora. They’re perhaps best known for use in tanning leather. But a lesser known property is tannin’s ability to inhibit the action of some viruses (Lu, 2004), bacteria such as Staphylococcus aureus (Akiyama, 2001), and flagellate protozoans (Kolodziej, 2005).
An interesting and welcome finding is that black tea may have the potential to stimulate insulin response and reduce blood sugar levels. Keeping those levels steady throughout the day can regulate appetite and reduce the tendency to snack, a definite asset in the battle of the bulge. Although green tea contains a higher percentage of polyphenols, the 5% – 10% found in black tea is sufficient to evoke the insulin response. Subjects who drank either 1.0 or 3.0 grams of black tea, contrasted to those who drank either glucose-laden or caffeine-laden water, experienced significantly lower glucose concentrations after two hours. Insulin levels had increased after ninety minutes (Bryans, 2007). Analysis of the tea discovered substantial polyphenol values. Almost twenty years earlier, reports showed that polyphenols from any source, in this case legumes, present a negative correlation with glycemic response (Thompson, 1984). The result held true for both diabetes and non-diabetes individuals.
With the exception of water, tea is the most popular beverage worldwide. Despite this, not much is known about the biological availability of black tea polyphenols or the molecular targets that mediate the glycemic effects. Aging and its related attributes appear to be linked to dietary cues, the complexity of gluconeogenesis among them. This metabolic pathway results in the generation of glucose from non-carbohydrate sources, such as from amino acids, including glycine, serine, arginine and glutamine, among others. In fact, only leucine and lysine are not glucogenic. Gluconeogenesis is a target for therapy in type 2 diabetes, which is address by metformin (Glucophage), a hypoglycemic agent that potentiates the action of insulin and inhibits glucose formation (Hunadl, 2000). The active polyphenols in black tea are identified as theaflavins and thearubigins.
Theaflavins are formed as green tea ferments into black or oolong tea. Already known to support lipid metabolism (Maron, 2003) (Lin, 2006), these compounds work with other polyphenols to present additional benefits, including attenuation of inflammation and oxidation (Aneja, 2004) (Leung, 2001). Thearubigins are likewise created, but also offer a reddish tone to a cup of brewed tea. If tea is poorly stored, thearubigins continue to form and adversely affect flavor while simultaneously reducing catechins, which control the qualities of green tea cited in the first paragraph. It is these components that boost the healthful properties of black tea. As they ply their talents, they prevent the glycation that lends itself to the formation of deleterious products that follow the heating of proteins in the presence of sugars, known in the culinary world as the Maillard reaction, or caramelization (Tan, 2008). Glycation risks the manufacture of a compound called methylglyoxal, an element that inhibits insulin signaling and contributes to the pathophysiology of diabetes (Riboilet-Chavey, 2006) (Tan, Apr 2008). By interfering with the production of one element in the process, we just might be able to forestall the ultimate villain—diabetes.
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