Consuming three or more cups of coffee a day lowers the risk of type 2 diabetes by 37 percent, a new study finds.

Previous studies have linked tea and coffee consumption to a lower risk of diabetes. Harvard University researchers conducted a study that is the first to look into how changes in coffee and tea consumption influence subsequent type 2 diabetes risk.

For the study researchers analyzed data from three US-based studies: the Nurses' Health Study (NHS), the NHS II and the Health Professionals. These studies were conducted between 1986 and 2007 and included participants aged between 25 and 75. Researchers collected detailed information regarding the participants' diets, lifestyle, medical conditions and other chronic diseases. This information was collected every 2 to 4 years over a period of 20 years.

The data helped researchers examine the associations between 4-year changes in coffee and tea consumption and risk of type 2 diabetes in the subsequent 4 years. During the study period, 7,269 participants developed type 2 diabetes. Researchers noted that people who increased their coffee consumption by more than 1 cup a day over a 4-year period experienced an 11 percent reduction in diabetes risk for the next four years. Consequently, those who reduced their coffee consumption by more than 1 cup a day over a 4-year period experienced a 17 percent hike in diabetes risk for the next four years. Researchers didn't find any association between change in tea consumption habits and diabetes risk.

"We found no evidence of an association between 4-year increases in tea consumption and subsequent risk of type 2 diabetes," the authors said in a statement. "This finding may have potentially been due to the relatively low number of participants who made significant changes to their tea consumption over a 4-year period thereby limiting statistical power to detect true associations. The overall low levels of tea consumption in this group may also be responsible for these findings."

Researchers also noted that people who drank three or more cups a day had a 37 percent lower risk of type 2 diabetes compared to those who drank less than one cup of coffee a day.

Though previous studies have also associated decaffeinated coffee consumption with lower type 2 diabetes risk, researchers didn't find any change in risk when decaffeinated coffee consumption was elevated or lowered.

"In these 3 large prospective cohorts with more than 1.6 million person-years of follow-up, we observed that increasing coffee, but not tea, intake over a 4-year period was associated with a lower type 2 diabetes risk in the next 4 years. Decreasing coffee intake was associated with a higher type 2 diabetes risk. These changes in risk were observed for caffeinated, but not decaffeinated coffee, and were independent of initial coffee consumption and 4-year changes in other dietary and lifestyle factors," the researchers said.

Researchers also noted that changes in coffee consumption affect diabetes risk in a relatively short amount of time.

Coffee has been subjected to both good and bad press. While it is said to have health benefits, including protecting against Parkinson's disease, type 2 diabetes and liver diseases, it has also been linked to obesity, hypertension and coronary heart diseases. For most people, the health benefits of coffee outweigh the risks, according to Donald Hensrud, M.D. of Mayo Clinic.

Of late, many studies have highlighted the benefits of coffee consumption. Earlier this month, researchers found that four or more cups of coffee a day can reduce liver cancer risk by up to 42 percent.  Another study highlighted that consuming two or more cups of coffee could reduce the risk of liver cirrhosis by up to 66 percent.

According to a National Coffee Drinking study conducted by the National Coffee association, more than 83 percent of American adults drink at least one cup of coffee daily. Among regular coffee drinkers, the average coffee consumption in the United States is 3.1 cups per day.

Statistics show that 8.3 percent of Americans have type 2 diabetes, of which, 27 percent cases go undiagnosed. It is also the primary cause of death for 71,382   Americans each year.

Findings were published in Diabetologia, the journal of the European Association for the Study of Diabetes. The study was funded by the National Institutes of Health. And supported by a postdoctoral fellowship grant from the American Heart Association.