Is Caffeine a Friend or Foe when Running?

On a recent training run where I overslept and ended up running in the brutal heat and humidity that is Virginia in July at 10AM, I had flashbacks to my experience during a Ragnar trail team relay event in 2017. My teammates and I all agreed that this was a one and done event for us! For some reason that particular year, Mother Nature decided that weekend in April was the perfect time to channel her inner summer and grace us with temps in the 90’s with super high dew points as well. It was lovely.

I found myself over caffeinated. I love Nuun, but I mistakenly brought only caffeinated flavors to this event. Plus, in an effort to stay awake when I needed to run during this 36 hour event, I also imbibed in way too much coffee. It was so hot and humid, I really needed the electrolyte replacements, but when paired with the extreme weather conditions, lack of sleep, and extra coffee, I found myself unable to even run the final loop. I walked most of it because my heart was racing, and I was overheated. I hope none of you ever go through what I did!

This experience has led me to choose my supplements more carefully, but I also wanted to explore the topic further. What does the science say about caffeine, and are there any studies about the effects of caffeine while exercising in hot, humid conditions?

Caffeine is one of the most common stimulants utilized. Do you have a relationship with it? I do. I faithfully drink my cup of coffee in the morning, enjoying that habitual boost of alertness it gives me, and then I generally abstain for the remainder of the day. I’m the type of coffee drinker that can’t have any past noon, or I won’t sleep that night! In hindsight, this should have been my first clue that I should not have overdone it at Ragnar. Maybe your relationship with coffee is a bit more freewheeling than mine. You may be the type of person who can’t get through your day without chugging multiple pots of it, and yet you still sleep like a baby all night. Or maybe you fall in between these two extremes.  

This knowledge about yourself should help guide you when choosing which supplements you will use for longer training runs. For those runners who are preparing for fall marathons, we are starting to reach the point in training already where we will be running double digits on the weekends. This means we will need to start to figure out what endurance supplements work for us, and which ones don’t. It’s different for everyone.

There are a plethora of choices at your local running stores, sporting goods stores, grocery stores, and even Amazon. Between electrolyte replacements, gels, and chews, it can become confusing and a bit overwhelming about what to try. Many of the commercially made supplements on the market also contain caffeine.

Just to give you a rough idea of caffeine content of supplements, I’ve given you some examples:

• Coffee: 80-100mg
• Clif Shotz with caffeine: 25-100mg, depending on flavor
• Extreme Sport Beans by Jelly Belly: 50mg per packet
• Gu with caffeine: 20-40mg, depending on flavor
• Nuun Sport with caffeine: 40mg
• Skratch Labs energy chews, sour cherry flavor: 50mg

It’s easy for the caffeine levels to accumulate if you choose only supplements with caffeine, as you can see.

Caffeine has been well studied as a safe energy boost during exercise and has been shown to reduce your perceived effort, but its use has been controversial. It was actually a banned substance in the Olympics from 1984-2004, and is currently on the watch list as a potential to be banned again by the World Anti-Doping Association.

So, we know that caffeine has benefits, but what are the down sides? My personal experience aside, here’s what the experts say about some of the negative effects from caffeine:

• Increased heart rate and blood pressure. This is a potentially compounding issue when paired with exercising in the heat and humidity, as this is also a side effect of training in the heat. Of course your heart rate increases with activity, but add the effects of caffeine and the stress of the heat, and your performance may suffer. Additionally, caffeine may delay recovery from elevated HR and BP with activity.
• Gastrointestinal distress. Most regular coffee drinkers are well aware of the fact that caffeine can have a laxative effect. Caffeine is also acidic and can irritate the lining of the GI tract, causing an upset stomach. Both of these phenomenons can make for a bad run!
• Diuretic effect. Increased urination can contribute to dehydration, but most of the studies I read did not support the theory that this risk was substantial.
• Anxiety/feeling jittery.
• Sleep disturbances.

Personally, I limit my caffeine consumption to my morning cup of coffee typically before a run. Once we start getting to 15 miles or more, I will keep one type of gel or chew that has caffeine, just in case I really need that extra kick. But, remember, my body is sensitive to its effects.

I’ve included some links to studies and articles on both the effects and safety of caffeine with exercise and safety with exercising in the heat below. The best study I found linking these topics had some concerns for me, including the small sample size of 16 cyclists, the fact that the participants were all male, and that the study was funded by a grant from Coca-Cola. Always follow the money, folks. The authors concluded that there was no danger to consuming caffeinated sports drinks during exercise in hot and humid conditions; the study also kept caffeine consumption well within recommended consumption limits.

As with most things in life, as you may have assumed, moderation is key. Caffeine can definitely be a friend, but there is such a thing as too much. So when you are choosing supplements for your runs, don’t exclusively choose the caffeinated ones. Have a plan to use these wisely, and practice before race day. According to the FDA, the recommended maximum dose per day is 400mg. It’s advisable to keep your daily consumption within these guidelines, including that morning cup of coffee!  Plus, you will feel a significant boost with the non-caffeinated versions simply with the sugar rush. I hope I’ve helped you make some balanced choices as you shop for supplements for your fall races, even if we end up running virtually this year.

What’s your experience with caffeinated supplements? While commercial supplements and electrolyte replacements are an important part of our tool bag for successful distance running, don’t underestimate the value of using real food during a run. I’ve personally benefitted from chewy candy and plain potato chips or pretzels during many a training run and race, and it’s a topic that ultra-runners love to discuss. But that’s a blog post for another day! Opinions are my own. As always, I hope you all are safe and healthy.

Resources and references:

Caffeine banned in the Olympics:

Can Olympic Athletes Have Caffeine?

Physiological changes due to training in the heat:

“Heat stress can reduce cardiac filling through pooling of blood in the skin and through reduced blood volume. Compensatory responses include reductions in splanchnic and renal blood flow; increased cardiac contractility, which helps to defend stroke volume in the face of impaired cardiac filling; and increased heart rate to compensate for decreased stroke volume.”

The splanchnic circulation consists of the blood supply to the gastrointestinal tract, liver, spleen, and pancreas. – Wikipedia

Safety with exercise in the heat

Summary of effects of caffeine on the body during exercise

General guidelines on safe use of caffeine to improve exercise performance

Supporting the safety of use of caffeine as a supplement to improve exercise

No statistically significant difference, but caffeine dose was within recommended limits.

Caffeine and recovery:

“…caffeine ingestion prior to moderate aerobic exercise delays recovery of the parasympathetic component of autonomic heart rate control, as well as the recovery of BP at baseline levels in young male participants.”

Study supported by a grant from Coca-Cola:

Mindy L. Millard-Stafford, Kirk J. Cureton, Jonathan E. Wingo, Jennifer Trilk, Gordon L. Warren, and Maxime Buyckx: Hydration During Exercise in Warm, Humid Conditions: Effect of a Caffeinated Sports Drink. International Journal of Sport Nutrition and Exercise Metabolism, 2007, 17, 163-177 © 2007 Human Kinetics, Inc.