Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Strong Evidence of a Genetic Link to Caffeine Cravings

Dear Doctor: Everyone in my partner's family loves coffee, but I'm like the rest of my family -- we can take it or leave it. Is it possible that a love of caffeine is in their genes?

Dear Reader: Surprising as it may seem, recent studies suggest that yes, for some people the craving for that first (and second and third) cup of daily coffee is actually built into their DNA. The bigger picture turns out to be even more interesting and a bit complex -- so first, a bit of background.

According to the National Institutes of Health, caffeine is the most widely used stimulant in the world. Found in coffee, tea, chocolate, colas, energy drinks and some medications, caffeine gives you a lift because it blocks a brain chemical called adenosine, which causes sleepiness.

Whether coffee is good or bad for you has been a source of conflicting medical opinion for quite a while. For every new study that finds the good -- increased concentration, elevated mood, decreased risk of some cancers and chronic diseases -- there's another study to highlight the bad. Coffee consumption has been linked to anxiety, insomnia, high blood pressure and an increased risk of heart attack.

Is the science on both sides of the caffeine debate wrong, or is it possible that something else is going on? In fact, scientists now believe your question hints at the answer. Not only does your DNA decide whether or not you will love coffee, the genes you carry determine how coffee will affect your body and your health.

In a study published in 2014, researchers compared coffee drinking habits among large groups of people of European and African-American descent. They also did genetic studies on each group. What they learned is that the ways in which you respond to coffee -- whether it wakes you up, makes you jittery, gets you inspired or gives you the shakes -- is coded into your genes. Depending on your specific genetic makeup, your body is either good at processing caffeine, or isn't efficient at all.

People in the study with the "fast" gene, which helps the liver to break down caffeine quickly, drank far more coffee than those with the "slow" gene. Researchers think that's because caffeine leaves their bodies so quickly, it takes a lot more coffee to keep the buzz going.

When scientists separated coffee drinkers into two groups, one with the fast gene and one with the slow gene, they had an aha! moment. The fast gene group of coffee drinkers actually showed a decreased risk of heart attack and hypertension. But people with the slow gene, which lets caffeine linger in the body and create more chemical interactions, had a greater risk of heart attacks and high blood pressure.

So barring a DNA test, how do you know how much coffee per day is safe to drink? Considering the many types of coffee-based drinks on the market right now, each with a different potency, it's best to think in milligrams.

Total caffeine in a cup of coffee, for example, can range anywhere from 50 to over 400 mg. Current wisdom is up to 400 mg of caffeine per day is a safe upper limit for healthy adults. But if even a cup of weak diner coffee gets your heart racing, then decaf -- or a glass of water -- is the safer bet.

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.)