Black and green tea are both made from the same Camellia sinesis plant, although different types processing give them different properties. For some time, it was believed drinking tea could interfere with your body's absorption of iron, which can cause anemia. Research has since determined tea doesn't cause anemia on its own, although it might make existing anemia worse.
Anemia
Anemia occurs when your body doesn't have enough healthy red blood cells to carry needed oxygen to your tissues. Symptoms typically include fatigue, irregular heartbeat, dizziness, shortness of breath, chest pain and pale skin. Although there are different types of anemia, the one affected by tea is known as iron-deficiency anemia. The two forms of iron include heme, from animal sources, and non-heme, from plants. A study published in "Critical Reviews in Food Science and Nutrition" in 2000 found that if you consume enough heme iron, you'll have a decreased risk of tea causing an iron deficiency.
How Tea May Affect Anemia
Nutritional scientists at Penn State University found that polyphenol antioxidants, ordinarily beneficial substances found in fruits and vegetables, may decrease the amount of iron the body absorbs and increase your risk of developing an iron deficiency. However, green tea leaves are steamed and dried, which preserves a higher level of polyphenols, whereas black tea leaves undergo an oxidation process that reduces polyphenol content.
Mitigating Factors
Scientists with the U.S. Department of Agriculture investigated iron absorption in laboratory rats over a long period of time. They were trying to determine whether the body adapts to tea consumption in a way that doesn't affect iron absorption, with a particular focus on polyphenols in tea called tannins. Their results, published in "Nutrition Research" in 2004, found that as rats became more accustomed to tea, their bodies absorbed significantly higher levels of iron than rats not consuming tea as often.
Contradictory Evidence
Another study, in the August 2008 issue of the "British Journal of Nutrition," followed 1,605 apparently healthy adults in South Africa who were ages 15 to 65. After analyzing their diets and the iron levels in the blood of the subjects, the researchers couldn't find a link between iron deficiency anemia or iron status among the subjects who were heavy tea drinkers.
Recommendations
Researchers in the U.K. looking at the association between anemia, iron and tea, published a review of studies in the "Journal of Human Nutrition and Dietetics" in 2004. They concluded that the evidence showed there was no reason to restrict tea drinking if you're healthy and have no risk of iron deficiency. If you are at risk, you may be able to drink tea between meals and wait at least one hour after eating before drinking tea. Check with your doctor if you already have anemia before consuming tea, since it could make your condition worse.
References
- MayoClinic.com; Anemia; February 2011
- "Critical Reviews in Food Science and Nutrition"; Effect of Tea and Other Dietary Factors on Iron Absorption; I.M. Zijp, et al.; September 2000
- "Nutrition Research"; Habitual Tea Consumption Protects Against the Inhibitory Effects of Tea on Iron Absorption in Rats; Hee-Seon Kim, et al.; 2004
- "British Journal of Nutrition"; Association Between Consumption of Black Tea and Iron Status in Adult Africans in The North West Province: The Thusa Study; P.S. Hogenkamp, et al.; August 2008
- "Journal of Human Nutrition and Dietetics"; Impact of Tea Drinking on Iron Status in the U.K.: A Review; M. Nelson and J. Poulter; February 2004
- Science Daily; Polyphenol Antioxidants Inhibit Iron Absorption; August 2010
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