The latest research, a scientific statement published by the American Heart Association in its journal Circulation, lands on a reassuring number: for most adults, up to 5 cups of caffeinated coffee a day—around 400 mg of caffeine—is safe and, for some people, may even be linked to a lower risk of several heart conditions.

There’s a catch that makes the exact count matter. In people with healthy blood pressure, drinking just 1 to 3 cups a day was associated with a higher risk of developing high blood pressure, while more than 3 cups was linked to a lower one—one of several findings that suggest a single morning cup may not be doing much for your heart either way.

Gregory Marcus, M.D., who chaired the statement’s writing group and is associate chief of cardiology for research at UC San Francisco Health, put it plainly: up to 5 cups a day “is safe and does not increase cardiovascular risk”—provided it’s black, without added sugars or fillers.

But the fine print cuts both ways. Drinking 2 to 4 cups of coffee a day was tied to a lower risk of heart disease, heart failure and stroke. Go past four, and the researchers warn the risk of heart failure may start to climb.

Your daily coffee intake, put to the test

The researchers at the University of California warned that in people with otherwise healthy blood pressure, drinking one to three cups a day was actually associated with an increased risk of developing high blood pressure. 

Drinking more than three cups a day was linked to a lower risk.

Caffeinated coffee may reduce insulin sensitivity in the short term, according to the review. But drinking it black and regularly, with no additives, flavors, or sweeteners, was linked to a lower risk of developing type 2 diabetes over time.

The researchers similarly concluded that drinking two to four cups of caffeinated coffee a day was linked to a lower risk of heart disease, heart failure, and stroke. 

“However, drinking more than 4 cups of caffeinated coffee a day may increase the risk of heart failure,” it warned.

Suggesting the sweet spot for workers wishing to reap the most success from their coffee habit is four cups a day.

But it’s worth noting: the benefits were linked to black coffee, with no milk or sugar. So this isn’t a green light to start guzzling caramel oat lattes in the name of your health.

The good news for tea drinkers—and the bad news for energy drinks

If coffee isn’t your thing, you’re not out of luck. The scientists noted that tea has also “been associated with reduced risk of atrial fibrillation, heart failure and stroke, similar to caffeinated coffee.”

Energy drinks, on the other hand, don’t get the same pass. 

The research warned that these performance-enhancing drinks can pack 40 to 69 mg of caffeine per fluid ounce. That is, three to four times more concentrated than a regular cup of coffee.

And the review found that higher caffeine intake at those levels was associated with real cardiovascular harm, including a higher risk of high blood pressure and irregular heart rhythm—even in people usually considered low-risk, like healthy adults under 30. 

It’s not the first time coffee’s reputation has been put under the microscope. Previous research has suggested your morning buzz might partly be a placebo—with the ritual of brewing and drinking it doing almost as much heavy lifting as the caffeine itself.

But the latest findings suggest one cup won’t cut it anyway. If you want the real payoff, you’ll need to go back for a second, a third, and ideally a fourth. Just don’t let your 4 p.m. slump convince you to reach for a fifth cup, or the energy drinks.