The report found that patients who drank coffee had a decreased risk for type 2 diabetes.
Caffeinated and decaffeinated coffee appeared to have similar effects, the researchers found.
The new report — from the Institute for Scientific Information on Coffee (ISIC) — included data from several past studies. According to the report, people who drank 3 to 4 cups of coffee a day were 25 percent less likely to develop type 2 diabetes than people who drank 2 cups or fewer.
Past research found that people who drank coffee were less likely to develop type 2 diabetes. Those who drank up to 7 cups of coffee a day were 50 percent less likely to develop diabetes than those who drank 2 cups or fewer, the new study found.
For each additional cup of coffee patients drank, they saw a 7 to 8 percent decrease in their risk of type 2 diabetes. Whether the coffee that patients drank had caffeine didn't appear to affect the results.
The ISIC report also noted that diabetes risk increased by 17 percent in people who decreased their coffee intake by 1 cup per day. People who increased their coffee intake by 1 cup per day, however, had an 11 percent lower risk of diabetes within the next four years.
Even the time of day patients drank coffee may have an effect on diabetes risk. In one study included in the report, French women who drank coffee at lunch were less likely to develop diabetes than those who drank coffee at other times.
Past research on whether caffeine played a part in coffee's potential effect on diabetes risk has produced conflicting results, however. The report authors called for further study on this topic.
Type 2 diabetes is a chronic disease in which the body cannot properly process the hormone insulin. Insulin regulates blood sugar. Diabetes can cause heart disease, blindness and kidney failure. Coffee may reduce blood sugar levels, according to the ISIC report, but more research is needed to confirm this effect. Coffee may also affect hormones that regulate insulin, the report authors noted.
Coffee may also improve liver function, which is necessary to keep blood sugar stable. The researchers were not sure exactly what components of coffee might decrease the risk of diabetes.
Too much caffeine can cause patients to have trouble sleeping or make them feel anxious or nervous. Patients should talk to their doctors before making large changes in their caffeine intake.
The Centers for Disease Control and Prevention (CDC) reports that 29.1 million people in the US have been diagnosed with diabetes. An additional 8.1 million have diabetes but have not been formally diagnosed, the CDC estimates. Diabetes is the seventh leading cause of death in the US.
In time to mark World Diabetes Day on Nov. 14, ISIC released this annual report on research related to coffee and type 2 diabetes Nov. 13.
ISIC is a nonprofit group. Members include seven of the major European coffee companies: illycaffè, Mondelēz International, Lavazza, Nestlé, Paulig, DE Master Blenders 1753 and Tchibo. ISIC supports independent research on coffee and shares research results.
Funding information for the studies in the report was not available. The report authors disclosed no conflicts of interest.