- The researchers investigated the effects of drinking different types of tea — such as green tea, oolong tea, and black tea — on the risk of diabetes.
- They found that drinking 1—3 cups of tea slightly reduced the risk of type 2 diabetes, but that drinking 4 or more cups of tea daily was associated with a 17% lower risk.
- However, further studies are needed to confirm the findings.
According to the World Health Organization, around 422 million people live with diabetes worldwide. The most common type is type 2 diabetes, which occurs when the body is unable to produce enough insulin or becomes resistant to insulin and cannot easily absorb insulin from the blood.
Some studies have found that tea and coffee consumption is associated with reduced overall mortality. Other research suggests that daily consumption of green tea has a lower risk of type 2 diabetes and a lower risk of overall mortality in people with diabetes.
Further studies on the effects of tea and dosage on diabetes risk in large population groups could inform prevention strategies for diabetes.
Researchers recently conducted a meta-analysis of 19 cohort studies from eight countries to investigate the effects of black, green and oolong tea consumption on type 2 diabetes risk.
They found that drinking 4 or more cups of tea a day may reduce the risk of diabetes.
“Drinking tea does not appear to be harmful and may provide a small advantage in reducing the risk of diabetes,” Dr. Kashif M. Munir, associate professor of medicine at the University of Maryland Center for Diabetes and Endocrinology, who was not involved in the study, told Medical News Today , “Other foods high in polyphenols have shown similar effects.”
The meta-analysis was presented at the annual meeting of the European Association for the Study of Diabetes in Stockholm, Sweden.
How many cups of tea?
For the study, the researchers analyzed data from 5,199 adult participants in the China Health and Nutrition Survey. The participants did not have diabetes at the start of the study and were followed from 1997 to 2009. Their tea consumption was collected using questionnaires.
In total, 45.76% of participants reported drinking tea and 10.04% of the cohort developed type 2 diabetes during the study period.
After adjusting for factors such as age, gender, and lifestyle, the researchers found that tea drinkers had a similar risk of type 2 diabetes as those who did not drink tea.
Next, the researchers conducted a systematic review of 19 cohort studies involving 1,076,311 participants, which examined the relationship between type 2 diabetes risk and tea consumption.
They were able to investigate the relationship between type 2 diabetes risk and the consumption of different types of tea — including green tea, oolong tea and black tea, frequency of tea drinking, gender, and living areas.
The researchers found that those who drank 1—3 cups of tea a day had a 4% lower risk of type 2 diabetes than non-drinkers.
However, those who drank at least four cups of tea a day had a 17% lower risk of type 2 diabetes than non-tea drinkers.
The researchers found that their results persisted regardless of the type of tea, gender, and living area. This suggests that the positive effects of tea on diabetes risk could be related to the amount consumed, as opposed to other factors.
How tea can lower the risk of diabetes
Asked how drinking tea could lower the risk of type 2 diabetes, Dr. Munir said:
“Tea is known to contain food polyphenols, such as EGCG, which have been shown to resist insulin and improve endothelial function ([which] are important for regulating the immune response, blood clotting, and dilating or narrowing blood vessels). These effects may have a positive effect on glucose homeostasis and improve the risk of diabetes.”
Other studies have found that green tea can lower blood sugar levels by increasing insulin production in mice. It is now known that black tea has a high content of theaflavins, which have antioxidant and anti-inflammatory effects.
Black tea may also inhibit obesity — a risk factor for diabetes — by promoting the transition from white fat to brown fat, thus aiding weight loss and blood sugar regulation; and lipid metabolism.
Researchers concluded that daily tea consumption reduces the risk of type 2 diabetes
A few things about tea
Professor Peter Clifton, associate professor of clinical and health sciences at the University of South Australia, asked about the limits of the study, who was also not involved. The study told MNT that this study was epidemiological in nature and could only identify possible links.
He added that double-blind, randomized controlled trials of dried tea extract in capsules versus placebos would need to be monitored over several years to obtain conclusive results.
“Suggesting tea drinking or drinking coffee as a lifestyle intervention isn’t going to work because people don’t suddenly change their ingrained habits of not drinking tea. So no reason to give it up, but not much evidence to pick it up.”
— Prof. Peter Clifton
Dr. Munir added that the first smaller cohort study showed no benefit from tea consumption, as observing small effects on large populations often requires a larger number of participants.
“The meta-analysis included over one million participants from 19 studies and showed the benefits of higher tea consumption combined with a lower risk of diabetes. Larger studies like this are often required to get a small benefit from a particular food,” he continued.
“The limitations, however, are that we don’t know whether the food is causal or is just an association with lower rates of diabetes development, and many prejudices may interfere with non-randomized trials,” he concluded.