Does Caffeine Help You Cruise — or Crash?

Written by By Donna Marlor, BSN, RD, CSSD (published from our archives)

I had just finished a 10k. Just finished. Face still red and flushed, sweat on my forehead, sensations heightened. My ears picked up a voice in the crowd calling for my attention: “What do you think about drinking coffee before a race?”

Huh? Still in a post-race endorphin-dazed state, I mumbled something about being a regular coffee drinker when the second question came. “Did you read about the study that said blood flow was reduced after drinking coffee?”

Now my brain started to click on again. I started thinking fast. My questioner was a fellow runner, as well as a science teacher. It turned out I actually knew him, but hadn’t seen him for quite a while. A serious runner (and a fast one), he looked truly concerned. I could tell he had been contemplating how painful Monday mornings would be without coffee.

“I just read this study published in the Journal of Cardiology,” he said. “Blood flow to the heart was reduced by 22 percent after drinking coffee.” By this time my brain had fully recovered and was going rapidly through the storehouse of exercise and caffeine files, coming up with mostly positive effects. But hmm, less blood means less oxygen. I was hearing his concern.

“I really wouldn’t worry about it. Caffeine also affects you up here,” and I pointed to my head, with a comment about reduction in perceived effort.  “My experience — caffeine plus sugar — hard to beat in a marathon.” However, the 22-percent-reduction-in-blood-flow finding stuck. Could going java-less be like legal EPO?

Caffeine and Your Heart

Having worked on a cardiac rehab unit, I know from experience that caffeine isn’t for everyone. “I just had a half a cup of coffee,” patients would confess, their faces crestfallen. The tell-tale monitor blipped irregular beats. For them, coffee plus the treadmill were not a healthy mix.

Caffeine isn’t harmless. And for someone with coronary artery disease, the reduction in blood flow leaves them with an oxygen deficit — placing more stress on their heart. But does that mean healthy athletes need to be concerned? Perhaps. At high doses (considered six to nine cups of coffee, or 700 mg – 900 mg of caffeine), studies done on fit army recruits show that detrimental side effects to mental performance and health become more common. However, individuals vary considerably in their tolerance to caffeine. Usual caffeine intake, body weight, timing of caffeine intake, and exercise intensity all factor into the performance-enhancement effects, or lack thereof.

Caffeine Reduces Fatigue

Athletes have known for years that a jolt of caffeine and sugar near the end of a race can perk them up like nothing else. If blood flow to the heart is decreased by caffeine, then what’s going on? J. Mark Davis, PhD., researcher and professor at the Exercise Science Department at the University of South Carolina, also asked that question. Working with rats as a model, he looked at the potential for caffeine to maintain optimal brain function and enhance exercise performance. According to Davis, when caffeine is injected into the brain, it blocks the rise of adenosine — a substance known to cause sleepiness and fatigue.

Although the adenosine-caffeine mechanism is still theoretical, the improvement of exercise time to exhaustion with caffeine use is well documented in a number of studies. Because voluntary movement is initiated by the brain, explains Davis, caffeine can improve exercise performance by decreasing the perception of effort and reducing pain sensation.

Caffeine and Performance

One of the small things in life I really look forward to is a great cup of coffee in the morning. So I took it upon myself to scrutinize the caffeine/exercise studies very carefully. Changing a morning routine that was coffee first, above all other things, was akin to getting a divorce.

For the sake of everyone else who would prefer to be out having some sort of recreational fun rather than reading research, I’m going to summarize in a few short words what I found in my hours of effort. Here are the highlights on caffeine effects, and some guidelines for using it to enhance performance without harmful side effects. But just in case you are in the mood to kick back and read through the details, the Institute of Medicine published a handbook titled “Caffeine for the Sustainment of Mental Task Performance,” prepared for the U.S. military.

Guidelines for Caffeine Use During Exercise

·       Coffee ≠ caffeine + water. Coffee has beneficial plant-derived compounds called polyphenols that have antioxidant effects. Moderate coffee use is associated with a decreased risk of type 2 diabetes, improved cognition and improved mood (including fatigue and sleepiness).

·       One cup of coffee may be enough. Although higher doses of caffeine were originally used to enhance exercise performance, low-to-moderate doses offer similar benefits. Aim for 3 – 6 mg/kg or 1.4 – 2.7 mg/lb of body weight.

·      Supplementation is most effective for non-users. Compared to regular caffeine users, non-caffeine users show greater improvements in performance when supplementing with caffeine before exercise. In cyclists doing time trial rides to exhaustion with equal supplemental caffeine (5mg/kg), non-caffeine users performed approximately 12 percent greater than caffeine users at one and three hours after caffeine ingestion. There were no differences at six hours out.

·       Avoid drinking coffee within one hour of exercise. Coffee has a similar diuretic effect to water. Pairing coffee with food will add sodium and help in retention of fluid.

·       Know the dose. Most energy drinks contain 70 – 200 mg of caffeine per serving. Most caffeinated soft drinks (16 oz) have about 50 mg per serving — about the same as a single shot of espresso.

·       Keep it under 300 mg. Caffeine in amounts of less than 300 mg per serving is safe for most people accustomed to using caffeine.

·       Race day isn’t a test run. Never try using caffeine to boost performance for the first time in a race. Your heart rate and adrenaline level are already elevated. Caffeine may just put you in the danger zone.

·       Get the “recovery edge.” After a bout of glycogen-depleting exercise, the addition of caffeine can speed the rate of glycogen replacement in a four-hour recovery period by as much as 66 percent. This rapid glycogen replacement requires a fairly high dose of caffeine (approximately 230 mg) immediately after exercise, followed by an additional 230 mg two hours later.

·       Legality. On January 1, 2004, caffeine was removed from the 2004 World Anti-Doping Agency (WADA) Prohibited List. This allows athletes who compete in sports that have adopted the 2004 WADA List to consume caffeine (within their usual diet or for specific purposes of performance enhancement) without fear of sanctions.

How Much Is Too Much?

How much is too much caffeine? Here are some warning signs that you may be overdoing it:

  • Irritability
  • Racing heart beat/high pulse
  • Irregular heart rate
  • Headache
  • Insomnia
  • Trembling
  • Anxiety
  • Inability to focus
  • High blood pressure

Caffeine Content

Take a look at the caffeine content (mg) of some common beverages. Be aware that for many products, one can or cup is more than the 8 oz serving listed here.

Brewed Coffee                            8 oz                                          95-200
Espresso                                     1 oz                                          50-75
Sports Energy Drinks                8 oz                                          76-280
Black Tea                                     8 oz                                       40 – 120
Green Tea                                    8 oz                                          32
Cola                                               8 oz                                          25

Adapted from USDA National Nutrient Database for Standard Reference, 2009; Center for Science in the Public Interest, 2007; Journal of Analytical Toxicology, 2008.