People who drink a lot of tea or coffee, even if it's decaf, seem to have a lower risk of developing type 2 diabetes, a new review has found.
In fact, the more coffee and tea people drink, the lower their risk of developing the potentially life-threatening condition, the analysis suggests.
The study, appearing in the Archives of Internal Medicine, was a meta-analysis, meaning it reviewed all the literature on coffee, tea, and diabetes risk. The researchers, led by Rachel Huxley, of the George Institute for International Health at the University of Sydney, narrowed their review down to 18 studies published between 1966 and 2009, involving almost 460,000 participants.
Six studies included information about regular and decaffeinated coffee and diabetes risk, and seven studies reported on tea consumption.
When the authors combined the data, they found that each additional cup of coffee consumed in a day was associated with a seven per cent reduction in diabetes risk.
People who drank three to four cups of coffee a day had about a 25 per cent lower risk of diabetes than those who drank two or fewer cups a day.
Those who drank more than four cups of decaf coffee per day had about a one-third lower risk than those who drank none. And those who drank more than four cups of tea had a one-fifth lower risk than those who drank no tea.
The researchers say the apparent protective effect of tea and coffee appeared to be independent of other factors that may raise the risk of diabetes, such as a high body mass index, increased age and family history of diabetes.
The review authors were quick to note that small-study bias may have had an effect on some of the numbers and might therefore lead to an overestimate of the magnitude of the link between the beverages and diabetes. Still, they say the reduced risk they noticed is worthy of further study.
As for why coffee and tea might lower the risk of diabetes, the authors say they're not sure. They note it's possible that heavy coffee and tea drinkers also eat healthier diets, which would help to protect them from the condition.
But it's also possible that there's something in coffee and tea that lowers diabetes risk. But that something is likely not caffeine, since even decaf coffee was linked to a lower diabetes risk.
Instead, other compounds in coffee and tea may be involved, including magnesium, antioxidants known as lignans or chlorogenic acids.
"The identification of the active components of these beverages would open up new therapeutic pathways for the primary prevention of diabetes mellitus," the authors write.
"It could also be envisaged that we will advise our patients most at risk for diabetes mellitus to increase their consumption of tea and coffee in addition to increasing their levels of physical activity and weight loss."
