The claim that drinking tea could protect people against developing type 2 diabetes was met with caution by several experts ahead of the annual meeting of the European Association for the Study of Diabetes.
The claim is that people who drink four or more cups of tea every day – especially green, Oolong or black tea – are 17% less likely to develop type 2 diabetes than those who don’t drink tea. Drinking fewer cups of tea per day was found to confer no benefit.
“Our findings are exciting because they suggest people can do something as simple as drinking four cups of tea a day to potentially lower their risk of developing type 2 diabetes,” said the University’s Xiaying Li. of Science and Technology in Wuhan (China). said in an official EASD press release.
“It’s possible that particular components of tea, such as polyphenols, lower blood sugar, but enough of these bioactive compounds may be needed to be effective,” Dr. Li added.
“The words ‘suggest’ and ‘potentially’ are crucial here,” Kevin McConway, PhD, MSc, MBA, professor emeritus of applied statistics at the Open University, said in a separate statement to the press that rocked the enthusiasm of Dr. Li. .
“Drinking tea would only be useful in reducing the risk of diabetes if drinking tea leads to a reduction in risk, i.e. if the risk is reduced if you drink tea and not if you do not. – and this study simply cannot show whether it does or not,” Dr. Conway pointed out.
Naveed Sattar, FMedSci FRCPath FRCPGlas FRSE, professor of metabolic medicine at the University of Glasgow, was also cautiously critical. “There is no strong evidence that the chemicals in tea prevent diabetes,” he observed separately.
“So I suspect that tea is healthier (lower calorie) than many alternative beverages or that tea drinkers lead healthier lives more generally.”
Dr Sattar added that it could be that people who drink tea also avoid drinking more harmful sugary drinks and engage in other health behaviors that could put them at lower risk for type 2 diabetes.
Time for tea?
Dr. Li will present the results of two analyzes on September 21 at the EASD meeting: the first a large observational cohort study and the second an updated systematic review and meta-analysis.
For the cohort study, Dr. Li and his coauthors collected data on more than 5,100 adults who had participated in the long-running and ongoing China Health and Nutrition Survey (CHNS). Information on tea-drinking behavior was extracted from questionnaires that had been completed at two points in time – 1997 and 2009 – and they determined whether people had developed type 2 diabetes according to American Diabetes Association criteria.
Almost half, 45.8%, were found to be tea drinkers and 10% of the sampled population had developed type 2 diabetes. However, no association between tea drinking and the development of type 2 diabetes was found, with the hazard ratio comparing tea drinkers and non-tea drinkers standing firmly at 1.02. Moreover, a sensitivity analysis excluding participants who developed type 2 diabetes during the first 3 years of follow-up did not change the result.
Things were slightly different when Dr Li and his associates carried out their meta-analysis which involved the analysis of data on more than one million participants in 19 studies conducted in eight countries which had been published up to September 2021.
Here they found that there was an important (P < 0.003) linear association between tea drinking and type 2 diabetes, with the relative risk of developing type 2 diabetes decreasing by 0.986 for each additional cup of tea drunk.
The RRs for the development of type 2 diabetes in tea drinkers compared to non-tea drinkers were 1.00 for those who drank less than one cup per day, 0.96 for those who drank one to two cups and 0.84 for those who drank four or more cups.
“Although further research is needed to determine the exact dosage and the mechanisms behind these observations, our results suggest that drinking tea is beneficial in reducing the risk of type 2 diabetes, but only at high doses (at least 4 cups a day),” Dr. Li said.
Perhaps “we did not find an association between tea consumption and type 2 diabetes in our cohort study because we did not examine higher tea consumption,” he said. she adds.
Storm in a teacup
“This is large observational data. This is not a randomized controlled trial, so there is plenty of room for the data to be misunderstood,” cautioned Matt Sydes, MSc, professor of clinical trials. and Methodology at the MRC Clinical Trials Unit, University College London.
“Everyone drinks liquids. If there’s an effect here (and that’s a big if), it might not be about the tea they drink, it’s about what they don’t drink. We cannot say at this time. It seems unlikely that a large randomized controlled trial could be done to resolve the ambiguity,” Dr Sydes added.
“Being only a conference abstract, it is difficult to assess the quality of this research,” said Baptiste Leurent, PhD, a medical statistician also working at University College London. Not only was the cohort study observational, but all the other studies included in the meta-analysis were also, he pointed out.
“Therefore, no causal conclusion can be drawn. The association could simply be due to other factors, such as those who drink more tea and have a healthier lifestyle. It does not seem that the authors tried to control for confounders, which is usually difficult in meta-analysis,” Dr. Leurent said.
“There’s reason to be a bit skeptical at this point; we really need to have all the details to assess it properly,” said Jonathan Cook of the University of Oxford’s Center for Statistics in Medicine. (England). “It’s a fair attempt to look at that, but not avant-garde, [using] pretty standard approaches.”
Similar studies have shown a reduced risk associated with coffee consumption, noted Duane Mellor, PhD, registered dietitian and senior lecturer at Aston University in Birmingham.
“The important take-home message is that lifestyle is important in managing the risk of developing type 2 diabetes,” Dr. Mellor said.
“This includes choosing low-calorie beverages, primarily water, and unsweetened tea and coffee, as beverages of choice as part of a healthy lifestyle.”
The study was funded by the Young Talents Project of the Hubei Provincial Health Commission, the Science and Technology Research Key Project of the Department of Education of Hubei Province, the Sanuo Diabetes Charity Foundation and the Xiangyang Science and Technology Plan Project, all based in China. Dr. Li had no conflicts of interest to disclose. Dr. McConway is a director and member of the Advisory Board of the Science Media Centre. Dr. Sattar has consulted for numerous companies that manufacture drugs for diabetes and cardiovascular disease and has participated in numerous trials of lifestyle approaches to the prevention and remission of diabetes. Dr. Sydes, Dr. Leurent, Dr. Cook and Dr. Mellor had no conflicts of interest to report.
This story originally appeared on MDedge.com, part of the Medscape Professional Network.
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