Take your coffee black, and it could help you live longer: That's according to a new study that found coffee drinkers tend to live longer, but only those who put little or no sugar and saturated fat in their beverages.

This notion coffee reduces the chance of an early death has been around for a while. Here the study team, led by researchers from Tufts University, wanted to look specifically at whether what you add to your coffee makes a difference.

"Few studies have examined how coffee additives could impact the link between coffee consumption and mortality risk, and our study is among the first to quantify how much sweetener and saturated fat are being added," says epidemiologist Bingjie Zhou from Tufts University.

"Our results align with the Dietary Guidelines for Americans which recommend limiting added sugar and saturated fat."

Related: Coffee Could Be The Secret to Healthy Aging For Women, Scientists Discover

The team crunched the stats on 46,332 US adults aged 20 or over, recorded in government health surveys, over the course of 9-11 years on average. In that time, 7,074 people died – deaths which were then cross-referenced against coffee consumption.

Coffee drinkers showed a notably lower risk of all-cause mortality, the researchers found, but when more than a little sugar and saturated fat (as found in full-cream milk or cream) was added to the mix, that statistical significance went away.

Overall, drinking black coffee or coffee with very low sugar and fat content was linked to a 14 percent reduction in the chance of an earlier death, compared to drinking no coffee at all. Between two or three cups a day seems to be the sweet spot.

While the researchers did factor in variables that might have affected mortality rates – including exercise levels, alcohol intake, age, sex, and education level – the study isn't thorough enough to prove direct cause and effect. There may still be unknown variables influencing both coffee drinking and all-cause mortality.

However, the data here does show a strong association, and does fit in with previous research into the health benefits of coffee. This study suggests that caffeine drives those benefits, as decaffeinated coffee drinkers saw no difference in mortality rates, and that sugar, milk, and cream might dilute the positive effects.

"The health benefits of coffee might be attributable to its bioactive compounds, but our results suggest that the addition of sugar and saturated fat may reduce the mortality benefits," says Fang Fang Zhang from Tufts University.

There's plenty more still to look into here, not least how the many different components of coffee might be protecting against an early death. There are likely to be numerous factors involved – including when you actually drink the stuff, as shown by a study published at the start of the year.

This new research is particularly helpful in that it isolates the coffee itself from anything else we may throw into it, which isn't the case for all studies like this – with each study often focusing on an angle of its own.

"Coffee is among the most-consumed beverages in the world, and with nearly half of American adults reporting drinking at least one cup per day, it's important for us to know what it might mean for health," says Zhang.

The research has been published in The Journal of Nutrition.