"Coffee drinkers are half as likely to develop diabetes as adults, research has found.
The study has caused controversy as caffeine is known to reduce the body’s sensitivity to insulin, the hormone diabetics need to treat their condition.
But the Dutch team behind the work say other components in coffee, such as magnesium and chlorogenic acid, could help prevent people developing Type 2 diabetes.
They say their findings should be examined in further studies, and that decaffeinated coffee could offer the same benefits, without the concerns over the effects of caffeine.
Diabetes experts in the UK said more needed to be known about why coffee drinkers had a reduced risk of developing Type 2 diabetes, and warned there were risks in drinking too much coffee.
Type 2, or non-insulin dependent diabetes is the most common form of the disease and usually occurs in people who are over 45 and overweight.
They do not make enough insulin, or cannot make proper use of it. This means they cannot move blood sugar into the cells. Sugar builds up in the bloodstream and causes health problems
Researchers from the Dutch national Institute for Public Health and the Environment in Bilthoven, Netherlands, asked over 17,000 how much coffee they drank each day.
Those who drank seven or more cups of coffee a day-were 50% less likely to develop type-2 diabetes compared with those who drank two cups a day or less.
The association was still seen when factors such as smoking, alcohol consumption and body mass were taken into account.
This study backs up previous research which showed that when people increased their coffee consumption for 14 days, their blood glucose levels were reduced, but substituting regular coffee for decaffeinated coffee for 20 days did not affect glucose levels.
That study did not include a control group, but the results suggested components of coffee other than caffeine could be beneficial for glucose metabolism.
Rob van Dam, who led the research, said: "In view of the widespread use of coffee and the large health burden of type 2 diabetes, our finding of an inverse association between coffee consumption and risk of type 2 diabetes could have important public-health implications.
“However, our findings need to be replicated and possible adverse effects on other health aspects should be considered in the choice to consume coffee.”
He told BBC News Online: "It has been shown over and over again that caffeine lowers insulin sensitivity. But they only study people for a few hours.
Exercise and diet
"If you look over several days, then there’s not such a clear effect - a tolerance of caffeine could develop.
“Decaffeinated coffee might have the same effects, and other types of coffee with more of the beneficial ingredients could be developed.”
Dr Amanda Vezey, a care advisor for Diabetes UK, said: "These are surprising results and we don’t know if this could really help people avoid diabetes in future.
"We need to find out what caused these results and that will need more research. Drinking more than seven cups of coffee a day will also have other side effects.
“If people really want to reduce the risk of diabetes regular exercise and a healthy diet are a safer and more reliable bet.”
The research is published in The Lancet."