Is caffeine of green tea & coffee good for diabetes?

Green tea for diabetes

According to the World Health Organisation, about 347 million people worldwide have diabetes mellitus.

Type 2 diabetes mellitus (T2DM) accounts for approximately 90% of all diabetes worldwide. 

Unfortunately, diabetes deaths are about to rise by more than 50% in the next 10 years.

Can food prevent or cure diabetes? Green tea for diabetes may be an important daily habit, as tea contains some phytochemicals that can prevent diabetes, along with other healthy dietary habits, and also it’s the most popular beverage worldwide, second only to water.

Dietary factors play a very important role in the control and prevention of type 2 diabetes (1).

Green tea for diabetes: control and prevention

Many modern studies have been conducted to investigate the association between tea consumption and diabetes risk.

Although the findings are controversial, there are many reports that showed moderately inverse associations between tea consumption and diabetes.

Role of caffeine in tea and coffee in diabetes

A study from the University of New York followed 7006 people and tried to find the relation between diabetes, coffee, and tea.

Increased consumption of coffee or regular tea found to decrease diabetes risk. Scientists said that the decrease in diabetes risk only applied to people under their 60s. Additionally, the decrease in diabetes risk only applied to those who had lost weight.

In conclusion, it was told that caffeine in beverages may help in diabetes-risk reduction (3). Certainly, you should avoid soda drinks containing caffeine. They’re probably high in sugar, calories, and artificial sweeteners, causing weight gain.

Dark chocolate contains moderate amounts of caffeine as well.

Certainly, you shouldn’t consume too much caffeine. It may cause side effects.

Moreover, the best time to consume coffee is 45-60 minutes before working or exercising.

Polyphenols and other antioxidants for diabetes

As there is a relation between coffee, tea and reduced risk of diabetes, scientists try to find out if caffeine or the antioxidants in tea or coffee benefit us the most.

Researchers from the University of Minnesota tried to study the possible connection between coffee intake and diabetes.

They found that caffeine isn’t so important as antioxidants.

Contrary, they suggest that coffee intake may be associated with reduced risk of type 2 diabetes mellitus because of minerals, phytochemicals, and antioxidants.

Tea is also rich in antioxidants, polyphenols, and other phytochemicals.

This study took place for 11 years. Scientists took data of 28812 postmenopausal women.

Finally, they showed that especially decaffeinated coffee intake, not the regular, was inversely associated with the risk of type 2 diabetes mellitus (5).

Health benefits of polyphenols
Tea is a good source of polyphenols.

Types of polyphenols in tea

There are 4 types of polyphenols. The tea polyphenols are called flavonoids.

The main reason that scientists try to find the correlation between tea and diabetes, is because flavonoids are powerful antioxidants.

As antioxidants, flavonoids in tea may prevent the progressive impairment of pancreatic beta-cell function due to oxidative stress and may this way reduce the occurrence of type 2 diabetes.

Another study tried to find the connection between polyphenols and diabetes. Although scientists didn’t find strong evidence that a high intake of flavonoids can reduce the development of type 2 diabetes, they did suggest consumption of tea and other foods rich in polyphenols, as they may have a modest inverse association of type 2 diabetes (4).

The most important conclusion of the scientists was that we should consume over 3 cups of tea daily, in order to have a lower diabetes risk.

How tea polyphenols protect from diabetes?

Tea polyphenols are called catechins and have an effect on obesity and diabetes. Especially EGCG, the most known tea catechin, appear to have powerful antiobesity and antidiabetic effects (2).

The exact mechanism for the beneficial effect by which tea may protect against the development of type 2 diabetes isn’t clear. But we know that tea (2):

  • improves insulin resistance,
  • impacts on hepatic gluconeogenesis. Gluconeogenesis occurs in the liver and kidneys. This process supplies glucose when it is needed between meals.
  • has a protective action on the pancreatic tissues. Both green tea and black tea preserve the mechanism that excretes insulin and also they protect pancreatic β cells.

Keeping that in mind, there isn’t any reason not to believe that antioxidants, polyphenols, and phytochemicals in all foods are the main reason for the reduced risk of diabetes.

The main daily sources of polyphenols are tea and coffee, as people consume large amounts of these beverages. The consumption of tea or coffee could easily increase the daily polyphenol intake by 500–1000 mg (6).

Polyphenols are so important for our health:

  • You can learn more about the importance of polyphenols and what foods are good sources of polyphenols here.
  • You can also learn more about the importance of tea in overall health, due to polyphenols, here.

Evidence doesn’t stop here…

Does tea or coffee consumption have an effect on diabetes?

Another Japanese study conducted in order to find any correlation between caffeine and diabetes. 17413 people were studied for 5 years.

Scientists came to the conclusion that the consumption of green tea, coffee, and total caffeine was associated with a reduced risk for type 2 diabetes. (7).

Another study designed to find a possible correlation between tea and coffee intake with the risk of diabetes. It is called the Singapore Chinese Health Study and analyzed health data from 36908 people.

Scientists observed a significant inverse association between coffee consumption and risk of incident type 2 diabetes mellitus.

Furthermore, they observed an inverse association between black tea consumption and incident type 2 diabetes in a population at high risk of developing type 2 diabetes (8).

These findings are important because coffee and tea are 2 of the most commonly consumed beverages worldwide.

How many cups of tea daily?

Participants who consumed more than 4 cups of coffee daily had a 30% reduction in the risk of diabetes compared with participants who didn’t consume any coffee.

Also, participants who consumed only 1 cup of black tea daily had a 14% reduction in the risk of diabetes compared with participants who didn’t consume any tea (8).

Other studies have found that 4 or more cups of tea consumption per day were associated with reduced type 2 diabetes risk by approximately 16% (1)

Many Japanese studies on tea and the effect on human health have found amazing results, for populations that consume large amounts of tea daily, even more than 10 cups per day.

For instance, ten cups of tea daily found to delay cancer onset by up to 8.7 years.

In conclusion…

Many experts suggest a minimum of three cups of coffee or tea per day, in order to have health benefits and lowering the risk of type 2 diabetes (9).

Above all, you shouldn’t drink hot tea or coffee. Hot foods and beverages are bad for your health. High temperatures may increase the risk of certain cancers!

Buy organic tea

Tea is a heavily produced herb. The demand is huge worldwide. It can be treated with pesticides to optimize production.

There are many cases that pesticide residue in tea. For instance, tea has been detected with the famous, now forbidden pesticide, DDT.

DDT was banned as a pesticide worldwide under the Stockholm Convention in 2001 after it was discovered to be dangerous to health, wildlife, and the environment.

But DDT continues to show up, as it becomes concentrated and passes through the food chain. Additionally, it may still be used in some third world countries.

Higher blood DDT level has been confirmed to be associated with a high prevalence of diabetes in the 1999–2002 National Health and Nutrition Examination Survey (1). 

Thus, whenever possible, buy organic tea to minimize exposure to pesticides.


  1. NCBI-PMC: Tea consumption and risk of type 2 diabetes mellitus: a systematic review and meta-analysis update
  2. NCBI: Tea, obesity, and diabetes.
  3. Greenberg JA, Axen KV, Schnoll R, et al. Coffee, tea and diabetes: the role of weight loss and caffeine. Int J Obes (Lond) 2005;29:1121–39
  4. Associations of dietary flavonoids with risk of type 2 diabetes, and markers of insulin resistance and systemic inflammation in women: a prospective study and cross-sectional analysis.
  5. Coffee consumption and risk of type 2 diabetes mellitus: an 11-year prospective study of 28 812 postmenopausal women.
  6. British Journal of Nutrition: Dietary reference intake (DRI) value for dietary polyphenols: are we heading in the right direction?
  7. The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults.
  8. Coffee, tea, and incident type 2 diabetes: the Singapore Chinese Health Study
  9. NCBI: Coffee and tea consumption and risk of type 2 diabetes.