Why do some people have laser focus after one cup of coffee while it seems others have to keep a pot brewing all day to just stay awake?

According to a report by Dr. J.W. Langer, a science journalist, genetic factors determine our reaction to caffeine.

He separates people into three groups of caffeine sensitivity:

  • Highly sensitive people metabolize caffeine slowly and have a nervous system that’s highly impacted by even low doses.
  • Regular sensitivity allows people to drink a few cups of coffee without disrupting sleep patterns or other adverse reactions.
  • Low caffeine sensitivity means a bedtime coffee has little or no effect on a person. You can drink coffee throughout the day without enjoying any increased alertness.

Caffeine sensitivity is determined by how each of us metabolizes caffeine and shouldn’t be confused with caffeine tolerance, which is simply how you respond to a caffeine dose.

While tolerance can build up over time, Langer said that your sensitivity is genetically determined and won’t change.

How much caffeine is too much?

According to the Mayo Clinic, about 400 milligrams of caffeine per day should be safe for most healthy adults.

This is the amount of caffeine in about four cups of coffee.

More than this amount could lead to a caffeine overdose. Some symptoms of too much caffeine include dizziness, nausea, and headache.

Barry Sears, PhD, creator of the Zone Diet and an expert on the dietary control of hormonal and inflammatory responses, told Healthline that overdosing on caffeine can also disrupt sleep and make you distracted, rather than focused.

Too much caffeine taken too often may also lead to caffeine addiction.

According to Sears, breaking the habit can be an uncomfortable experience.

“Caffeine addicts may have to deal with headaches when they try to cut back,” he said.

Sears added that excess caffeine intake can make you insensitive to normal fatigue signals from the brain, which is why he describes caffeine as “the most widely used psychoactive drug in the world.”

Your best caffeine doses

Finding your best caffeine dose for alertness, without discomfort or the risk of becoming addicted, can be tough.

New research from the U.S. Army has found a way that researchers say can help you discover the dose you need to maintain peak alertness.

In a study published in the Journal of Sleep Research, Department of Defense researcher Jaques Reifman described how a new algorithm can inform anyone about the best amount of caffeine to take at the right time.

According to Reifman, a high-performance biotechnology software researcher for the U.S. military, the algorithm can identify the best caffeine dose that will result in a level of alertness that makes us most productive.

Reifman had study participants perform psychomotor vigilance tasks. He then recorded their sleep and caffeine intake data (since caffeine affects everyone differently).

His algorithm then calculated the ideal dosage strategy for each person, depending on that information.

Since Reifman’s algorithm depends on performance tasks, you don’t need to know how caffeine-sensitive you are. He says it will tell you the best dose regardless.

“Our algorithm is the first quantitative tool that provides automated, customized guidance for safe and effective caffeine dosing to maximize alertness at the most needed times during any sleep-loss condition,” said Reifman in a press release.

The price you pay

As enjoyable as that morning cup can be, excess caffeine consumption can extract a price later on.

“The energy you get is balanced by increased fatigue later on as the brain tries to get back to normal,” said Sears.

However, Reifman said his research may soon give us an app that tells the perfect time and dose to get the most benefit.

“We found that by using our algorithm, which determines when and how much caffeine a subject should consume, we can improve alertness by up to 64 percent, while consuming the same total amount of caffeine,” Reifman said.

The algorithm is currently being tested as an app with soldiers in training. The Army has plans to license it.

While this caffeine algorithm is still not available for civilians, a less personalized 2B-Alert mobile app using the new algorithm is available now.