Recently I’ve talked with several long distance runners —­­ think half-marathon or marathon — and have been surprised to hear how many down a mug of coffee before they race.

After all, doesn’t coffee cause dehydration, something runners would like to avoid?

A PLOS ONE study published in early January suggests the answer is no, at least for those people who regularly drink the beverage.

U.K. researchers found drinking around four cups of coffee per day was no more dehydrating than drinking the same amount of water for the 50 male coffee drinkers included in their study.

That’s good news for many of us who enjoy the drink, runners or not. But when it comes to running, some of the runners referenced coffee’s ability to enhance performance due to its caffeine content. I decided to do a little investigating to see if my morning mug is actually helping my daily workout.

Consuming caffeine appears to improve performance for running and other endurance sports, such as cycling, according to one 2008 review. Most of the studies used to draw this conclusion looked at doses of caffeine around 2 to 3 milligrams per kilogram body weight. That’s about the same amount of caffeine in 4 8-ounce cups of coffee consumed by a 150-pound person.*

Caffeine may also be beneficial for intense bouts of running, cycling, or swimming, up to 20 minutes in length, while the review found less evidence for consuming caffeine to beef up one’s abilities in team sports.

However, just because caffeine has been shown to benefit performance doesn’t mean caffeine in the form of coffee will be equally effective.

One of the authors on the PLOS ONE coffee-and-dehydration study, Asker Jeukendrup, investigated this question in another PLOS ONE study published in 2013.

Jeukendrup and his U.K. colleagues found that caffeine in the form of coffee produced similar improvements in endurance exercise as pure caffeine, at least for higher doses (equivalent to 5 milligrams per kilogram body weight or around eight 8-ounce cups of coffee for a 150-pound person). However, previous studies found coffee to be less effective.

Wherever the research falls, anecdotally, the runners I know suggest pre-race coffee is a go.

For more on the topic, check out the American College of Sports Medicine’s Current Comment Fact Sheet on the issue.

*Coffee varies in its caffeine content, but the USDA cites an 8-ounce cup as having 95 milligrams of caffeine. Of course, the cup of coffee you buy may be more than 8 ounces; a “tall” at Starbucks is 12 ounces.