People who drink coffee regularly may lower their risk of developing type 2 diabetes.

But don’t count on a daily jolt of java to fend off diabetes just yet.

The researchers reporting the finding aren’t advising coffee as a diabetes prevention method.

They say they found support for the idea that “habitual coffee consumption is associated with a substantially lower risk of type 2 diabetes.”

However, more studies are needed, they write in The Journal of the American Medical Association.

Read WebMD's "Do You Know the Right Way to Drink Coffee?"

Grounds for Research

One of the researchers was Rob M. van Dam, PhD. He works in the nutrition department at Harvard School of Public Health.

He and his colleagues didn’t do a new experiment. Instead, they reviewed 15 past studies of coffee and type 2 diabetes.

Nine studies were done over a long time -- six to 20 years. They included a combined total of more than 193,000 people in the U.S. and Europe.

Read WebMD's "Coffee: The New Health Food"

Coffee Findings

People who drank the most coffee had the lowest risk of type 2 diabetes.

They downed at least six or seven cups of coffee per day. They were 35 percent less likely to develop type 2 diabetes as those who drank less than two cups of coffee daily.

Those who drank four to six cups per day had a 28 percent lower risk of type 2 diabetes, compared with people who drank the least coffee, say the researchers.

Similar patterns were seen in six other studies. Those were one-time-only checks; they didn’t track diabetes risk over time. More than 17,000 people took part in those projects.

Read WebMD's "Important Tips for Diabetes Prevention"

Filtered, Instant, Decaf Brews

Been in a coffee shop lately? If so, you’ve seen the array of coffee styles.

If coffee has some advantage against diabetes, does it matter what kind you drink?

The findings mainly reflect consumption of drip-filtered coffee. The studies didn’t have as many drinkers of instant or unfiltered coffees, say the researchers.

What about decaf coffee? The European studies didn’t distinguish between caffeinated and decaf coffee and diabetes risk.

But decaf coffee was associated with lower type 2 diabetes risk in two U.S. studies, say the researchers.

Milk & Sugar

Do milk and sugar make a difference?

A Swedish study tracked insulin sensitivity when milk, cream, or sugar was added to coffee or tea.

Insulin is a hormone made by the body to control blood sugar.

In that study, insulin sensitivity dropped when sugar was added to coffee or tea. Insulin sensitivity didn’t change when only milk or cream was added, say the researchers.

“For most people, the amount of sugar and milk added to coffee is small compared to other food sources,” say van Dam and colleagues.

Read WebMD's "Diabetes Diagnosis Is Traumatic for Parents"

Pattern, Not Proof

Coffee wasn’t directly tested for diabetes prevention. No one was asked to change their coffee consumption.

The coffee drinkers weren’t healthier. “Higher coffee consumption was generally associated with a less healthy lifestyle,” say the researchers.

Future work should examine coffee’s key ingredients, say van Dam and colleagues.

“Currently, it is premature to recommend increasing coffee consumption as a public health strategy to prevent type 2 diabetes,” they write.

“Other health effects of coffee should also be considered.”

A study reported by WebMD showed that regular coffee drinkers had more stiffness to major blood vessels compared with noncoffee drinkers. Decreased elasticity of major blood vessels is a risk factor for developing heart disease including heart attack and stroke. Heart disease is a leading killer in the U.S.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCE: van Dam, R.M. The Journal of the American Medical Association, July 6, 2005; vol 294: pp 97-104.