While overconsumption of caffeine can have a negative effect on performance, normal consumption can be helpful.

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At a recent seminar, the presenter — a friend of mine — seemed anxious on stage. He kept pacing back and forth and wiped sweat from his brow several times. At the break, I went up to him and asked, “Are you doing OK? Would you like me to get you a glass of water?”

“I’m fine,” he replied. “I think I just had a little too much caffeine this morning. I was really tired and wanted to be on my game. Guess the shot of espresso I added to my drip coffee wasn’t such a great idea after all.”

We Seattleites love our coffee. We’re actually 94 percent more likely to prefer espresso to bottled water than the average American. But too much caffeine could negatively affect your work performance.

How much coffee is the right amount?
According to Cristen Harris, PhD, RD, CSSD, assistant professor in the Department of Nutrition & Exercise Science at Bastyr University, “The optimal amount varies for each person and is related to their individual tolerance and sensitivity. Sensitivity to caffeine depends on a variety of individual factors, including how much and how often caffeine is habitually consumed, body weight, physical condition and overall anxiety level.”

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Average caffeine consumption in the U.S. is 200 mg, or about two cups of coffee, per day. But Harris points out that caffeine levels in coffee can vary based on the roast, brewing method and even the amount of grounds used per cup.

“For example, a lighter roast has a higher caffeine content than a darker roast,” says Harris. “To put the caffeine content of coffee in perspective for Seattleites, a 16-ounce [grande] cup of Starbucks’ Pike Place Roast coffee has approximately 330 mg of caffeine, compared to about 25 mg in the decaffeinated Pike Place Roast.”

Too much can hurt work performance
As my friend found out during his presentation, too much caffeine can have a detrimental effect on performance. “Overconsumption of caffeine can cause anxiety, jitters and nervousness,” Harris says. “It can also cause an inability to focus, digestive discomfort, insomnia and irritability.”

There are a lot of other sources for caffeine, such as tea, chocolate, soda, energy drinks and even some non-prescription medications — all of which can increase the amount of caffeine in the body.

… But a smaller amount can be good
While overconsumption of caffeine can have a negative effect on performance, normal consumption can be helpful. “Studies show caffeine improves mood, mental fatigue, reaction time, alertness, visual attention and other computerized attention tasks,” says Harris.

I’ll drink to those coffee benefits! Or maybe I shouldn’t … I’ve already had my two cups today.

Lisa Quast is the founder of Career Woman, Inc., and the author of the book Secrets of a Hiring Manager Turned Career Coach. Email her at lquast@careerwomaninc.com.