This is not meant to keep you awake at night, but heavy coffee drinkers are at increased risk of early death, according to a major study.
For reasons that researchers don't fully understand, a 17-year study of 45,000 people shows those aged under 55 who average more than 28 cups a week are at risk.
It's not that people are dying at a rapid rate. But men who drink more than four cups a day are 56 per cent more likely to die and women have double the chance compared with moderate drinkers, according to the The University of Queensland and the University of South Carolina study.
Cardiovascular disease is not a major factor and people aged older than 55 do not appear to be adversely affected, say the authors of the report published in the journal Mayo Clinic Proceedings.
"It could be the coffee, but it could just as easily be things that heavy coffee drinkers do," says The University of Queensland's Dr Carl Lavie.
"We have no way of knowing the cause and effect."
However, the statistics have been adjusted to remove the impact of smoking.
Close to five per cent of people in the study died during the 17 years.
"It's not as if people are dying like flies because they are drinking coffee. But it is statistically significant," says Dr Lavie.
"We are not trying to scare people, but I do think it makes sense to keep average coffee consumption to two to three cups a day."
This does not mean people should be afraid to occasionally have more than that, he says.
Senior investigator Steven Blair of the University of South Carolina says it is significant the results do not show an association between coffee consumption and people older than 55.
It is also important that death from cardiovascular disease is not a factor, he says.