Drinking more than 28 cups of coffee a week or four cups a day may be bad for under-55s, according to a study by The University of Queensland and the University of South Carolina.
Dr Carl Lavie of the Department of Cardiovascular Diseases, University of Queensland's at the Ochsner Medical Center in New Orleans said the study suggested heavy coffee consumption could be toxic to younger people.
Dr Lavie said the study, published in the journal Mayo Clinic Proceedings involved medical questionnaires completed by almost 45,000 people between 1979 and 1998.
Men under the age of 55 who drank about 28 cups of coffee each week were 56% more likely to die from all causes, and younger women who drank similar amounts of coffee more than doubled their risk of mortality.
No adverse effects were found in heavy coffee drinkers aged over 55.
“There continues to be considerable debate about the health effects of caffeine, and coffee specifically, with some reports suggesting toxicity and some even suggesting beneficial effects,” Dr Lavie said.
“Recent research has found that coffee is one of the major sources of antioxidants in the diet and has potential beneficial effects on inflammation and cognitive function.”
“However, it is also well-known that coffee has potential adverse effects because of caffeine's potential to stimulate the release of epinephrine, inhibit insulin activity, and increase blood pressure and levels of homocysteine.
“Thus, all of these mechanisms could counterbalance one another.
“Moderation is the best advice," Dr Lavie added.
He further added that studies were needed in different populations.