Grow Youthful: How to Slow Your Aging and Enjoy Extraordinary Health
Grow Youthful: How to Slow Your Aging and Enjoy Extraordinary Health

Black tea prevents a variety of diseases, but it can be dangerous too

Black tea prevents Parkinson's disease, glaucoma

Black tea is high in fluorides, especially Kenyan-grown tea

Tea bags


Tea originated in China, and most green tea still comes from China. The four biggest tea-producing countries today are China, India, Sri Lanka and Kenya. Together they represent 75% of world production. Tea was introduced into India in 1823. India and Sri Lanka (Ceylon) then became the world's biggest suppliers of black tea. In the 1960's tea plantations were established in Kenya, primarily in the Eastern Rift Valley.

Black tea helps reduce stress and cortisol levels. (10)

Black tea is high in tannin, a compound that binds a variety of micronutrients, particularly vitamin B1, calcium, iron and zinc. If you drink several cups of black tea per day, it may be wise to monitor for symptoms of deficiency of zinc and thiamine (B1). However, calcium should never be supplemented in the form of a pill as I explain in Grow Youthful. Iron is another element that should not be supplemented except by menstruating women who need it as confirmed by a blood test. (6, 7, 8, 9)

Some, but not all tea is very high in pesticides, aluminium and heavy metals. By far the worst offender is China, with one study showing the level of these pollutants twenty nine times (yes, 29) higher than the average of other countries. For this reason it is worth looking carefully at the label and avoiding Chinese-grown teas. (4, 5)

Black tea prevents Parkinson's disease, glaucoma

Time to enjoy a cuppa. In the Grow Youthful green tea web page, I explain how green tea is usually renowned as the drink with most health and longevity benefits, more than the standard black tea that most people drink. But is this really correct - when is black tea more healthful? Black tea includes Earl Grey and English Breakfast.

A large study (1) in Singapore showed that black tea may be able to slash the risk of getting Parkinson's disease by almost a third. Researchers found that people who drank the most black tea were 29 percent less likely to develop Parkinson's disease, compared with those who drank little or no black tea. At first the researchers thought the higher level of caffeine in black tea was responsible for the benefit, but it turned out not to be so. Instead, it appears that black tea somehow affects the level of estrogen in a way that prevents Parkinson's. Interestingly, the disease is less common in women than in men, which again points to this female hormone.

In contrast, green tea showed no protective effects against Parkinson's disease.

A 2017 study (2) of 1,700 adults in the USA found that 5% of them had glaucoma. It found that participants who consumed hot tea (normal black tea, with caffeine) daily were 74% less likely to have glaucoma than those who did not consume hot tea. However, the consumption of coffee, iced tea, green tea and decaffeinated tea had no effect on the risk of glaucoma.

The above benefits of tea apply only to black tea. As explained in Grow Youthful, adding milk and sweeteners turns it into a harmful beverage. If you want to have white tea, then use full-fat cream.

Black tea is high in fluorides, especially Kenyan-grown tea

Tea is sometimes the worst food/drink source of fluorides, depending on where the tea is grown.

Kenya's Eastern Rift Valley region has the highest concentration of fluorides in the soil in the world, and this is where Kenyan tea is grown. The entire population of the region is chronically poisoned by fluorides, and many studies show poor health and a high incidence of a variety of ailments. Tea grown in the Kenyan Eastern Rift Valley has a level of fluorides about ten times higher than teas from India and China. (3)

The longer the tea is brewed, the more fluoride is released into the brew.

Drinking black tea during pregnancy is associated with spina bifida. (3)

When purchasing tea, ensure that the source is clearly labelled, and if the source is unclear or it is a blend of tea from different countries, avoid it.

How to remove fluorides and protect yourself from them.

Tea bags

Tea bags were not a healthy invention. Tea bags are usually bleached with chlorine compounds, so if you insist on using tea bags because of their convenience, choose bleach-free bags. However, if you want to enjoy the full health benefits of tea and also a much higher quality tea, buy loose-leaf tea rather than tea bags. If you open a tea bag and look at the tea inside, you will see that the tea is in a form of small pellets rather than tea leaves. The tea in tea bags is of a lower quality because the manufacturers can use the smallest tea dust and sweepings plus a binding agent to hold them all together. In contrast, when you look at loose leaf tea you can see that you get proper tea leaves.


1. Tan, L. C. et al. Differential effects of black versus green tea on risk of Parkinson's disease in the Singapore Chinese Health Study. American Journal of Epidemiology 2008 Mar 1;167(5):553-560.

2. Connie M Wu1, Annie M Wu1, Victoria L Tseng, Fei Yu, Anne L Coleman. Frequency of a diagnosis of glaucoma in individuals who consume coffee, tea and / or soft drinks. British Journal of Ophthalmology. Published online 14 December 2017.

3. Declan T. Waugh, William Potter, Hardy Limeback, Michael Godfrey. Risk Assessment of Fluoride Intake from Tea in the Republic of Ireland and its Implications for Public Health and Water Fluoridation. Int J Environ Res Public Health. 2016 Mar; 13(3): 259. Published online 26 Feb 2016. doi: 10.3390/ijerph13030259. PMCID: PMC4808922. PMID: 26927146.

4. Liu J, Lu W, Zhang N, Su D, Zeer L, Du H, Hu K. Collaborative Assessment and Health Risk of Heavy Metals in Soils and Tea Leaves in the Southwest Region of China. Int J Environ Res Public Health. 2021 Sep 27;18(19):10151. doi: 10.3390/ijerph181910151. PMID: 34639452; PMCID: PMC8508298.

5. Zhang J, Yang R, Chen R, Peng Y, Wen X, Gao L. Accumulation of Heavy Metals in Tea Leaves and Potential Health Risk Assessment: A Case Study from Puan County, Guizhou Province, China. Int J Environ Res Public Health. 2018 Jan 13;15(1):133. doi: 10.3390/ijerph15010133. PMID: 29342877; PMCID: PMC5800232.

6. Vimokesant S, Kunjara S, Rungruangsak K, Nakornchai S, Panijpan B. Beriberi caused by antithiamin factors in food and its prevention. Ann N Y Acad Sci. 1982;378:123-36. doi: 10.1111/j.1749-6632.1982.tb31191.x. PMID: 7044221.

7. Kositawattanakul T, Tosukhowong P, Vimokesant SL, Panijpan B. Chemical interactions between thiamin and tannic acid. II. Separation of products. Am J Clin Nutr. 1977 Oct;30(10):1686-91. doi: 10.1093/ajcn/30.10.1686. PMID: 20773.

8. Rungruangsak K, Tosukhowong P, Panijpan B, Vimokesant SL. Chemical interactions between thiamin and tannic acid. I. Kinetics, oxygen dependence and inhibition by ascorbic acid. Am J Clin Nutr. 1977 Oct;30(10):1680-5. doi: 10.1093/ajcn/30.10.1680. PMID: 910744.

9. Delimont NM, Haub MD, Lindshield BL. The Impact of Tannin Consumption on Iron Bioavailability and Status: A Narrative Review. Curr Dev Nutr. 2017 Jan 19;1(2):1-12. doi: 10.3945/cdn.116.000042. PMID: 29955693; PMCID: PMC5998341.

10. Steptoe A, Gibson EL, Vuononvirta R, Williams ED, Hamer M, Rycroft JA, Erusalimsky JD, Wardle J. The effects of tea on psychophysiological stress responsivity and post-stress recovery: a randomised double-blind trial. Psychopharmacology (Berl). 2007 Jan;190(1):81-9. doi: 10.1007/s00213-006-0573-2. Epub 2006 Sep 30. PMID: 17013636.