Additionally, the researchers found that heavier coffee drinkers were more protected against diabetes than those who drank less.
"Ask your doctor about ways to prevent diabetes."
Xiubo Jiang, Dongfeng Zhang and Wenjie Jiang, of the Department of Epidemiology and Health Statistics at Qingdao University, conducted the review on coffee and type 2 diabetes.
Type 2 diabetes occurs when the body loses sensitivity to insulin, a substance that regulates blood sugar. As a result, people with type 2 diabetes have chronically high blood sugar.
To see how coffee drinking habits might affect a person's risk of developing type 2 diabetes, the researchers looked at previous trials and studies involving coffee and caffeine intake.
They looked at studies that exposed participants to either coffee or caffeine and looked for type 2 diabetes as an outcome. Additionally, they attempted to find out if the risk changed depending on the amount of coffee consumed.
The researchers examined 26 articles that discussed 31 total trials. A total of 1,096,647 people participated in the trials, and 50,595 participants developed type 2 diabetes.
The trials had follow-up periods ranging from 2.6 years to 24 years. Most of the trials followed up for more than 10 years.
The researchers determined that the participants who drank the most coffee were about 30 percent less likely to develop type 2 diabetes as those who drank the least amount.
They also found that the risk was reduced more for women who drank coffee than for men who drank coffee.
In terms of the dose response, the researchers found that the incidence of type 2 diabetes decreased by 12 percent for every two daily cups that the participants drank.
The risk reduction was similar for the 13 studies involving decaf coffee. Those who drank the most decaf were about 21 percent less likely to develop diabetes as those who drank the least.
Caffeine alone also led to a reduced risk of type 2 diabetes in the six articles that the authors reviewed. Those in the group that consumed the most caffeine were about 30 percent less likely to develop type 2 diabetes as those who consumed the least.
The researchers concluded that there may be an inverse relationship between coffee and caffeine consumption and cases of type 2 diabetes.
Additionally, the protection that coffee may offer against diabetes increased as participants drank more.
The authors of the review called for more long-term trials to confirm their findings.
This review was published in the European Journal of Nutrition in October.
The authors declared no conflicts of interest and did not provide any information about funding sources.