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18-01-2011 | Diabetes | Article

Oolong tea consumption linked to diabetes in Japanese men


Free abstract

MedWire News: Japanese men who regularly drink two or more cups of oolong tea per day have an increased risk for developing diabetes compared with non consumers, say researchers.

Yasuaki Hayashino (Kyoto University, Japan) and colleagues analyzed data from 4975 men, aged 38.3 years on average, participating in the High-risk and Population Strategy for Occupational Health Promotion Study (HIPOP-OHP). They assessed associations between baseline intake of oolong tea, commonly consumed in China and Japan, and incident diabetes over 3.4 years of follow-up.

In total, 201 cases of incident diabetes were recorded during the follow-up period. Men who drank 1 cup of oolong tea per day or less did not have a significantly increased risk for developing diabetes compared with nonconsumers.

However, men who regularly consumed 2 or more cups per day had a significant 64% increased risk for Type 2 diabetes compared with nonconsumers. This association continued to be valid after adjustment for various confounders.

The team found that fasting blood glucose increased by 0.11, 0.12, and 0.15 mmol/l per year in men who drank 0, 1, and 2 or more cups of oolong tea per day, respectively.

The findings contrast with those of previous studies showing a protective effect of coffee and tea drinking against diabetes, as reported by MedWire News.

"These results from the HIPOP-OHP study suggest that high oolong tea consumption is associated with a statistically significant increase in the risk of diabetes in relatively healthy Asian male workers via an effect on fasting plasma glucose levels, even after adjustment for a large number of possible confounders," write the authors in the journal Diabetic Medicine.

"However, our observational study cannot prove a cause-effect relationship, and it is premature to recommend that the consumption of oolong tea be stopped as a means of preventing diabetes."

They suggest: "Further long-term metabolic studies are required to investigate the long-term effects of oolong tea consumption on glucose homeostasis, insulin resistance and energy expenditure."

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Helen Albert