Researchers have found even more evidence that coffee can be good for you. People who drink regular, moderate amounts of coffee are less likely to die from a range of diseases, from diabetes to heart disease.

The cutoff seems to be around five cups a day, and even decaf coffee helps, the team at Harvard University’s school of public health found.

But even heavy coffee drinking doesn’t appear to offset the damage caused by smoking, they report in the journal Circulation.

“The main message is that regular consumption, meaning three to five cups of coffee a day, is associated with lower risk in total mortality and mortality from several causes like diabetes, cardiovascular disease and suicide,” Frank Hu, a professor of nutrition and epidemiology who helped lead the study, told NBC News.

“In previous studies on that issue, most of the coffee was caffeinated coffee. In our study, both caffeinated and decaffeinated coffee showed a lower mortality risk but there is no final conclusion yet.”

"In our study, both caffeinated and decaffeinated coffee showed a lower mortality risk."

Hu and colleagues looked at two giant sources of information: surveys of more than 200,000 doctors and nurses who have regularly updated researchers on their eating and other lifestyle habits and details about their health for more than 20 years.

Coffee drinkers overall were less likely to die over the decades than non-drinkers. The effects were even stronger and clearer when the team discounted smokers. Non-smokers who drank coffee were between 8 and 15 percent less likely to die, depending on how much they drank.

“This is good news for people who drink coffee because the evidence is strong. Drinking coffee may be good for health outcome,” Hu said.

It’s not a clear correlation. People who drink more coffee also are more likely to smoke, drink, and to eat red meat. Other lifestyle habits may also go along with heavy coffee drinking, and the researchers didn’t report on whether people drank their coffee black, with cream, with sugar, or as giant frothy drinks from coffee store chains.

“We are not advocating coffee as a strategy for prevention of the chronic diseases because coffee drinking is individual behavior and there are other factors in the diet that have a bigger effect. People should also be aware of the amount of added sugar to coffee drinks which can become a problem,” Hu said.

What could coffee be doing for health? The dark drink is the No. 1 source in the American diet of antioxidants – those chemical compounds that fight the damage to your DNA caused by day-to-day living.

“The main message is that people who enjoy drinking coffee should not worry about it being harmful for their health."

Other research has found evidence that coffee can help people recover from colon cancer, lower diabetes risk and reduce the inflammation associated with diabetes and heart disease.

Advisers to the U.S. government say new dietary proposals should mention the benefits of coffee, which include protection against diabetes, Parkinson's and liver cancer.

“The chlorogenic acid, lignans, quinides, trigonelline, and magnesium in coffee reduce insulin resistance and systematic inflammation,” the researchers wrote.

“This is probably the best study we are going to get because of the very large numbers, the inclusion of men and women, and the decades of follow-up,” said cardiologist Dr. Sharonne Hayes of the Mayo Clinic in Minnesota, who wasn’t involved in the study.

“The main message is that people who enjoy drinking coffee should not worry about it being harmful for their health,” Hayes told NBC News. “Coffee may actually be beneficial to their health.”