Each morning, billions of people reach for that familiar cup of Joe. The aroma of coffee fills kitchens all around the world and for many people, morning doesn’t start without a cup. For many, it’s comfort. For others, caffeine. But a new study suggests it might also be something more profound: a subtle boost to longevity — so long as you keep it simple.

Researchers at Tufts University’s Friedman School of Nutrition Science and Policy have found that drinking one to three cups of black coffee a day may reduce the risk of death from any cause by 17%. Yet if you’re spooning in sugar or splashing in cream, those potential benefits may vanish.

What’s brewing beneath the surface

The study, which was published in The Journal of Nutrition, draws from nearly two decades of national survey data spanning from 1999 to 2018. Researchers analyzed dietary recalls from more than 46,000 Americans, cross-referencing them with mortality data from the National Death Index.

The main focus was how much coffee people drank but people also dug deeper. They looked at what type of coffee they drank and how much sugar and saturated fat they stirred into their cups.

The results were striking: adults who drank one to two cups of caffeinated coffee daily had a 14% lower risk of death from all causes compared to non-coffee drinkers. For those sipping two to three cups, the risk dropped by 17%. But the protective effect plateaued at higher doses — and faded almost entirely when the drink was doctored with too much sugar or cream.

“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,” said first author Bingjie Zhou, a recent Ph.D. graduate from the nutrition epidemiology and data science program at the Friedman School. “Our results align with the Dietary Guidelines for Americans which recommend limiting added sugar and saturated fat.”

What qualified as “low” was very little. The team defined low sugar as less than 2.5 grams per 8-ounce cup — about half a teaspoon — and low saturated fat as under one gram, the amount in a tablespoon of half-and-half. Anything more tipped the balance toward risk.

Unfiltered coffee

Coffee is a complex drink. It’s not just the caffeine inside, there’s chlorogenic acid, polyphenols, and other plant compounds that have been linked to antioxidant, anti-inflammatory, and even anti-cancer effects. But unfiltered coffee also contains compounds that can raise your cholesterol, and previous studies have suggested that filtered coffee may be better for your health.

But those same studies have sometimes ignored the modern coffee habit: sugar-laced, cream-heavy beverages that can rival milkshakes in calories. This new study puts that part of the conversation back in.

This study doesn’t claim causation. It’s observational, meaning researchers can’t say for certain that coffee extends life. Other factors — like diet, income, or genetics — could be in play. The data also came from a single 24-hour dietary recall, which has its limits. Still, the sample size and duration of the study lend weight to the findings.

The new research adds a dose of nuance to years of glowing headlines about the health benefits of coffee. Yes, your morning brew might help you live longer. But only if it’s closer to what your grandparents drank — black, hot, and unsweetened.

“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,” said Fang Fang Zhang, senior author of the study and the Neely Family Professor at the Friedman School. “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.”