D: Yaël, this coffee is just so good!

Y: It is so good, especially in the morning.

D: It's especially helpful when my get up and go, has gotten up and went!

Y: Y'now, Don, I have a slight caffeine addiction myself.

D: Did you know that people's caffeine sensitivity falls into one three levels?

Y: I wonder which category I'm in.

D: Well, people can be hypersensitive to caffeine, when just a tiny bit of coffee can give them intense jitters. At the other end of the spectrum, about ten percent of the population is hyposensitive to caffeine. These folks process caffeine so efficiently that they can drink a huge cup of coffee and then go straight to sleep. Most people, however, fall into the level of normal sensitivity to caffeine, which means that caffeine will energize them, but not impact them adversely, so long as they drink it earlier in the day.

Y: I probably have a normal sensitivity.

D: That all depends on your CYP1A2 gene, which controls how your liver metabolizes caffeine and affects your sensitivity to it.

Y: It sounds like they know quite a bit about caffeine tolerance, or intolerance, as the case might be.

D: Oh, that's not all. The Harvard School of Public Health conducted a study on 120,000 people. They discovered six genetic variants, in which two genes impact how people metabolize caffeine, two genes that regulate the fat and sugar in our bloodstream, which itself impacts how we respond to caffeine. Then they found two other genes that are connected with our sense of satisfaction, or reward, related to caffeine. These factors, beyond our sensitivity, in turn affect our potential addiction to caffeine.