When you make coffee with breakfast, or grab a to-go cup at a cafe before work, or raid your office’s break room for a cup in the afternoon, you’re probably not thinking about how scientists are studying it.

So we’ll just tell you: Many studies have looked at the health effects of coffee, even though measuring the potential harms and benefits is not as easy as chugging a shot of espresso. Since a whole range of lifestyle and genetic factors influence a person’s physical well-being, it’s hard to know exactly if, or how, or to what extent, coffee would be good or bad for anyone’s longterm health.

The latest study, published in Mayo Clinic’s Proceedings [PDF], found an association between drinking more than 28 cups of coffee a week and an increased risk of death from all causes, in people 55 years old and younger. One cup of coffee is 8 ounces.

That doesn’t prove that coffee causes death. It also seems to contradict a study in the New England Journal of Medicine last year, which found that people who drink two or more cups of coffee a day have a reduced risk of dying from particular diseases than those who consume little or no coffee.

And a May 2011 study found that men who drink six or more cups a day had a decreased risk of fatal prostate cancer.

How are we supposed to decide how much coffee to drink, when the information about its health effects is more confusing than a cafe menu written in a foreign language?

Experts say that the optimal dose of coffee varies widely, depending on the person. Different people have different tolerances for coffee.

But in general, the authors of this new study emphasized a message of moderation.

The new study 

Researchers followed more than 40,000 people ages 20-87 for about 16 years.

They observed risks for heavy coffee drinkers in both men and women under 55 who drank more than four cups of coffee a day on average. In men who fit this description, the risk of death was 56% higher compared to non-coffee drinkers. In women, the risk was even greater – it doubled, compared to non-coffee drinkers.

The same association was not observed in individuals 55 and older, or in people who drank coffee in moderation.

“It appears that low doses of coffee are safe,” said Carl J. Lavie, study co-author from the John Ochsner Heart and Vascular Institute in New Orleans. ”We did not see anything bad happening up to about 28 cups per week.”

He added, “no increase in cardiovascular mortality at any dose in men or women at any age” was seen.

Caveats

But wait! Although study authors found a connection between heavy coffee consumption and death, they did not prove that frequent java indulgence causes death. There may be other underlying factors that explain this association.

“What if people are super hyper, driven, stressed out, drinking 10 cups of coffee a day?” Lavie said. “And it’s not the coffee that’s killing them, it’s the fact that they’re stressed out that’s killing them.”

Lavie still suggests that heavy coffee drinkers scale back on their consumption, however.

“I think that if I find that having four or more cups of coffee per day looks like it’s associated with higher mortality, even though I don’t know that it’s for sure due to the coffee, to me that’s enough reason to me to try and keep my coffee to below four a day.”

The authors did not separate decaf coffee from regular, but ”most people report they drink regular,” added Dr. Xuemei Sui, study co-author from the Arnold School of Public Health at the University of South Carolina.

They also did not explore what people were adding to their coffees, so they didn’t separate out whether the addition of sweeteners or milk had any effect on death risk.

But what about coffee benefits

There is, on the other hand, evidence from studies on type II diabetes suggesting that coffee can be good.

According to a 2009 meta-analysis, the risk of type II diabetes goes down with each cup of coffee consumed daily. Additionally, a 2007 meta-analysis found a correlation between increased coffee consumption and lower risk of liver cancer.

Such research is still not persuasive enough to tell anyone who doesn’t already drink coffee to start.

How much coffee do you drink? 

“A 20 ounce cup, we would count that as two and a half cups,” Lavie added.

For perspective, here are some measurements of that cup o’ Joe you like to enjoy:

A short Starbucks coffee is 8 ounces. A tall is 12 ounces. A grande is 16 ounces, or two cups of coffee. Make it a venti and you’ve consumed 20 ounces.

Meanwhile, at Dunkin’ Donuts, a small cup of coffee is 10 ounces. A medium contains 14. Order a large and you’ll get ounces 20 ounces and XL, 24 ounces, or three cups of coffee.

Experts told CNN in 2012 that they would not make a public health recommendation concerning coffee because there just isn’t enough solid evidence to do so.

“If you consume coffee, enjoy it,” Dr. Donald Hensrud of the Mayo Clinic said. “But I wouldn’t necessarily recommend taking it up if you don’t like it.”

A lot of people already consider it a regular part of their lives. For nearly two-thirds of Americans, the daily coffee routine is just habit.

Get out of bed. Make coffee. Start your work day.

Have more coffee. Repeat.  Hope it won’t kill you.