Can caffeine help people with chronic kidney disease live longer?

That's the suggestion of a new study that found that among more than 2,300 Americans with chronic kidney disease, those who drank the most caffeinated drinks reduced their risk of premature death by 24 percent.

"Our study showed a dose-dependent protective effect of caffeine consumption on all-cause mortality among patients with chronic kidney disease," said lead researcher Dr. Miguel Bigotte Vieira, from the Centro Hospitalar Lisboa Norte, in Lisbon, Portugal.

"However, our observational study cannot prove that caffeine reduces the risk of death, but only suggests the possibility of such a protective effect," he said.

Moreover, the reasons that caffeine might be protective aren't clear, and how much caffeine is too little and how much might be too much also isn't known, Bigotte Vieira added.

The findings also need to be replicated in a trial that compares caffeine consumption with no caffeine consumption before patients are counseled to drink more coffee or other caffeinated drinks, he noted.

In the study, the research team found that:

those who consumed the least amount of caffeine saw no reduction in death risk,

those who had the second higher amount reduced their risk by 12 percent,

those who had the third higher amount reduced their risk by 22 percent,

and those who consumed the most caffeine reduced their risk by 24 percent.

The association between caffeine and a reduced risk of premature death was independent of factors such as age, gender, race, family income, education, creatinine levels (a marker of kidney troubles), high blood pressure, smoking, high cholesterol, body weight, previous cardiovascular problems and diet, Bigotte Vieira said.

The findings were to be presented Friday at the American Society of Nephrology annual meeting, in New Orleans. Research presented at meetings is considered preliminary until published in a peer-reviewed journal.

Dr. Leslie Spry, from the Lincoln Nephrology & Hypertension, Dialysis Center in Nebraska, said, "I hope this is the case, as I sit here and drink my morning coffee." Spry is also a spokesman for the National Kidney Foundation.

"As you know, there are studies of coffee being harmful, beneficial and having no effect on health," he said.

This is yet another observational study, Spry noted, where only an association was found, not cause and effect.

Given the relatively small size of the study, and the small reduction in death risk, Spry said he's not willing to tell kidney patients that the more caffeine they drink, the longer they'll live.

"I would rather say that compared to little or no caffeine intake, those people with the highest intake of caffeine as estimated by dietary recall, may have a lower mortality, but the reason for this lower mortality is not proven by additional research.

"I would rather say that compared to little or no caffeine intake, those people with the highest intake of caffeine as estimated by dietary recall, may have a lower mortality, but the reason for this lower mortality is not proven by this association research," he said.