People who report drinking three to five cups of coffee per day are less likely to die prematurely from heart disease, suicide, diabetes or Parkinson's disease, US researchers said.



Both caffeinated and decaffeinated coffee were shown to have benefits, said the study by researchers at the Harvard University Chan School of Public Health published in the November 16 edition of the journal Circulation.



The study compared people who don't drink coffee, or drank less than two cups daily, to those who reported drinking "moderate" amounts of coffee, or up to five cups daily.



The study did not prove a cause-and-effect for coffee and the reduced likelihood of certain diseases, but uncovered an apparent link that aligns with previous research, and that scientists would like to probe further.



"Bioactive compounds in coffee reduce insulin resistance and systematic inflammation," said first author Ming Ding, a doctoral student in the Department of Nutrition.



"That could explain some of our findings. However, more studies are needed to investigate the biological mechanisms producing these effects."



No protective effect was found against cancer in this study. Some previous research has pointed to a link between coffee consumption and a lower risk of certain cancers.



The study was based on data gathered from three large, ongoing surveys including some 300,000 nurses and other health professionals who agree to answer questionnaires about their own medical conditions and habits at regular intervals over the course of 30 years.



"In the whole study population, moderate coffee consumption was associated with reduced risk of death from cardiovascular disease, diabetes, neurological diseases such as Parkinson's disease, and suicide," said the findings.



Researchers also accounted for potential confounding factors such as smoking, body mass index, exercise, alcohol consumption, and diet. But the fact that the research relied on surveys, which use self-reported behavior, could raise questions about its reliability.



And experts warned that coffee -- a substance adored by many devotees -- may not be right for everyone.



"Regular consumption of coffee can be included as part of a healthy, balanced diet," said senior author Frank Hu, professor of nutrition and epidemiology at Harvard.



"However, certain populations such as pregnant women and children should be cautious about high caffeine intake from coffee or other beverages."