The infusion of leaves from the plant Camellia sinensis in hot water, a practice that has existed for centuries, creates the popular drink known as tea. The concept originated in China and spread worldwide from there. Black tea, green tea and white tea leaves are all derived from the same plant. The difference is in the age of the leaves or the process the tea is put through. For example, white tea leaves are very young when harvested, and green tea is not put through the same fermentation process that black tea is.
Antioxidants
Antioxidants are compounds that are able to donate electrons to molecules called free radicals. Free radicals are unstable molecules that need to acquire an electron to gain stability. When a free radical steals from a healthy body cell, it damages the cell. This process is referred to as oxidation, and antioxidants play an important role in preventing or slowing the process when they donate an electron. It is important to maintain a continuous supply of antioxidants in the diet, as once an antioxidant has donated an electron it is no longer an antioxidant.
Properties of Tea
Tea contains many beneficial compounds, including flavonols, a type of antioxidant. Polyphenols in the form of catechins are also present in tea. Catechins are cardioprotective because of their antioxidant function. A study published in the May/June 2005 issue of "Annals of Nutrition and Metabolism" stated that epidemiological studies show an inverse relationship between the consumption of tea and heart disease risk.
Components of Milk
Milk contains fat, carbohydrate and protein. The fat content is altered during processing to produce whole, 1 percent, 2 percent and skim milk. Carbohydrate in the form of lactose is responsible for the slightly sweet taste of milk. The protein in milk is in the form of casein molecules, which bind together to form micelles, or spherical groupings. Milk contains many other proteins, known as whey proteins. These proteins are suspended in the whey, the portion of milk left behind when the casein proteins coagulate into curds.
Milk in Tea
The effects of milk in tea are varied. The possibility that proteins in milk may inhibit the antioxidant activity of tea by binding the antioxidant compounds has been the subject of much research. A study published in the November 2006 issue of the "European Heart Journal" found that black tea alone enhanced blood flow within two hours of consumption. When milk was added to the tea, the casein in milk inhibited these beneficial effects by binding the tea catechins. However, a study published in a 2001 issue of "Free Radical Research" found that milk in tea did not change the subjects' plasma concentrations of flavonols absorbed from tea. Milk may not affect the absorption of antioxidants from tea, but it may affect how they function in the body.
References
- "Free Radical Research"; Addition of Milk Does Not Affect the Absorption of Flavonols from Tea in Man; Peter C.H. Hollman, et al.; 2001
- "Critical Review in Food Science and Nutrition"; Tea Catechins and Polyphenols: Health Effects, Metabolism, and Antioxidant Functions; Jane V. Higdon and Balz Frei; January/February 2003
- "European Heart Journal"; Addition of Milk Prevent Vascular Protective Effects of Tea; Mario Lorenz, et al.; November 2006
- "Annals of Nutrition and Metabolism"; Addition of Milk Does Not Alter the Antioxidant Activity of Black Tea; Reddy VC; May/June 2005
- "Krause's Food, Nutrition, and Diet Therapy"; L. Kathleen Mahan, et al.; 2004
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