We hear quite a bit about the importance of antioxidants, which are natural substances in foods that prevent or delay some types of cell damage.
According to the National Center for Complementary and Integrative Health, our body is under assault from a variety of free radicals. Free radicals are unstable molecules that can cause oxidative stress that damages our cells and which is thought to play a role in a variety of diseases such as cancer, cardiovascular disease, diabetes, Alzheimer’s, Parkinson’s, cataracts, and age-related macular degeneration. Free radicals are formed in our bodies from environmental sources such as air pollution and cigarette smoke, and they are also part of our bodies’ natural processes, formed when we exercise or when our bodies digest food.
Antioxidants have been shown to decrease oxidative stress from free radicals in laboratory experiments as well as in animals, and there is ongoing research and debate about the potential beneficial role of antioxidants for humans.
Antioxidants and Green Tea:
Drinking green tea is associated with a lower incidence of cardiovascular disease and cancer where oxidative stress plays an important role.
The strongest antioxidants identified in green tea are the flavonols epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). While several research studies show the helpful antioxidant effect of these flavonols in animal studies, the results from human studies are inconsistent. Some epidemiological studies of the association between tea consumption and cancer risk show reduced risk of cancer of the colon, breast, ovaries, prostate, and lungs. Limited scientific research suggests the possibility of green tea reducing blood pressure and cholesterol levels, although more research is needed.
The inconsistent results could be dependent on the amount of tea consumed, how oxidative stress is measured, and the amount of oxidative stress in the research subjects. Other variables include genetic variations in how people respond to the antioxidants in tea and lifestyle factors that may influence the risk of cancer or cardiovascular disease such as body weight, physical activity, and tobacco and alcohol use. How the green tea is prepared also makes a difference in antioxidant content. For the highest number of antioxidants, brew green tea in boiling water for 5 minutes. Instant tea, iced tea, and ready-to-drink teas contain far fewer antioxidants.
Cautions with Green Tea:
Tea is generally recognized as safe by the U.S. Food and Drug Administration.
While drinking green tea as a beverage is considered safe, green tea extracts may lead to liver problems in some people.
Tea naturally contains caffeine, and negative effects associated with caffeine include erratic heart rate, insomnia, restlessness, nervousness, headache, and nausea. The current recommendation is that adults consume no more than 400mg of caffeine per day. The amount of caffeine present in tea varies by the type of tea.
- Black teas contain the highest amount of caffeine, ranging from 64 to 112 mg per 8 fl oz serving
- Oolong tea, which contains about 29 to 53 mg per 8 fl oz serving, is next in line.
- Green and white teas contain slightly less caffeine, ranging from 24 to 39 mg per 8 fl oz serving and 32 to 37 mg per 8 fl oz serving, respectively.
- Decaffeinated teas contain less than 12 mg caffeine per 8 fl oz serving.
Both black and green tea inhibit the absorption of iron from foods consumed at the same time as the tea. Drinking tea between meals or including a source of vitamin C such as oranges or grapefruit improves iron absorption.
Green tea has also been shown to reduce the effectiveness of nadolol, a beta-blocker used in people with high blood pressure and heart problems.
Green tea may also interact with other medications. Check in with your doctor if you have any concerns.
Our Best Green Tea Tips:
Brew your own green tea at home, steeping it for 5 minutes in boiling water.
Make your own iced green tea by letting brewed tea cool and then adding ice cubes. You can even make ice cubes out of brewed green tea!
Avoid adding sugar to green tea, since added sugar increases oxidative stress in your body. Instead, brew green tea with flavorful herbal teas such as lemon or raspberry.
By Lynn Grieger, RDN, CDE, CPT, CHWC
- U.S. Department of Health and Human Services. National Institutes of Health. National Center for Complementary and Integrative Health. Antixoidants: In Depth. https://nccih.nih.gov/health/antioxidants/introduction.htm last updated November 2013. Accessed 10-29-18
- Peluso I, Serafini M. Antioxidants from black and green tea: from dietary modulation of oxidative stress to pharmacological mechanisms. Br J Pharmacol. 2016;174(11):1195-1208.
- National Institutes of Health. National Cancer Institute. Tea and Cancer Prevention. https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/tea-fact-sheet?redirect=true Reviewed November 17, 2010. Accessed 10-30-18.
- U.S. Department of Health and Human Services. National Institutes of Health. National Center for Complementary and Integrative Health. Green Tea. https://nccih.nih.gov/health/greentea Updated September 2016. Accessed 10-30-18.
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.