#142 Is Caffeine Safe for the Heart?

Is Caffeine Safe for the Heart?

New research reports that caffeine does not cause an irregular heart beat, palpitations, or heart arrhythmias.  Can we really believe the results of this new study?  Read on to see my answer to the question, is caffeine safe for the heart?

Mark’s Experience

Mark was a 46 year old man who came to see me for palpitations and a rapid heart beat.  Mark was tired all of the time.  The only thing that could get him through the long work day was Red Bull and Monster energy drinks.

He typically started off the day with a Red Bull.  In the afternoon, when energy levels were at the lowest, he would switch to Monster.  Sometimes, if he was really tired, he might add in a third energy drink or even a cup of coffee.

To identify the cause of his palpitations and rapid heart beat, I had him wear a heart monitor.  After just a few days it was obvious what was going on.

His palpitations clearly correlated with premature heart beats arising from his ventricles or PVCs.  The rapid heart beat coincided to short episodes of a heart arrhythmia called atrial fibrillation.

Fortunately, Mark’s stress echocardiogram and other tests were completely normal.

Knowing about the reported possible heart dangers of energy drinks, I asked him to stop the energy drinks.  I also encouraged him to eat healthier, exercise every day, and make sleep a priority.

When he came back to see me a month later, he reported that his energy levels were much better.  His symptoms were also completely gone.

Initially, I suspected it was the eliminating the caffeine from the energy drinks that did the trick.  I was surprised to find out that while he no longer drank energy drinks, he was now eating dark chocolate on most days.  With this new information, it became clear to me that perhaps caffeine was not the cause of his heart troubles.

Latest Study on Caffeine and Abnormal Heart Rhythms

This past week, a new study was published by my colleagues at the University of California, San Francisco  (UCSF) on the effects of caffeine to the heart’s rhythm.  As might be expected, as soon as this study was published, headlines around the world reported “Caffeine May Not Cause Palpitations.”

In this study, UCSF cardiologists recruited 1,388 participants in this study.  As part of this study, participants reported their coffee, tea, and chocolate intake.

To measure the effect of coffee, tea, and chocolate on the heart, participants also wore heart monitors to record every heart beat.  When UCSF cardiologists reviewed their heart monitors, they found no correlation between the number of irregular heart beats and caffeine intake.  In other words, regardless of their caffeine intake, it did not seem to affect how many premature atrial contractions (PACs) or premature ventricular contractions (PVCs) study participants had.

Limitations of this Caffeine Arrhythmia Study

Does this study mean that people who suffer from heart arrhythmias can have all the caffeine they want?  Not so fast.  This study leaves many questions unasnwered.  In my opinion, there are three big limitations of this study.

1. This was an observational study.

As an observational study we can’t conclusively say that caffeine from coffee, tea, or chocolate doesn’t cause heart arrhythmias.  All we can say is that, for whatever reason, the amount of caffeine consumed from coffee, tea, and chocolate in this study, did not seem to affect the number of irregular heart beats.

There could be other reasons why these study participants were not affected by caffeine.  Perhaps these people practiced mindfulness techniques, like meditation or yoga, to control stress and keep irregular heart beats at bay with increasing doses of caffeine.

2. This study did not include caffeine from other sources.

Study participants were only asked about coffee, tea, and chocolate consumption.  They were not asked about caffeine from other sources.  For example, researchers had no idea if study participants were also drinking Diet Coke or Red Bull.

3. This study did not compare fast versus slow caffeine metabolizers.

It is possible that most of the study participants were fast caffeine metabolizers.  For fast caffeine metabolizers, caffeine consumption has little affect on the heart.

Fast vs. Slow Caffeine Metabolizers

Does caffeine make it hard for you to sleep at night?  If so, then chances are that you are part of the 50% of people who have a genetic variant to your CYP1A2 gene.

Variations in the CYPA12 gene can cause you to metabolize caffeine more slowly.  Indeed, based on your genetics, there can be up to a 40-fold difference in how fast caffeine is metabolized in your body.

These genetic differences may explain why some studies report that caffeine may be dangerous to your heart and other studies, like the one discussed in this artice, report that caffeine is safe.  Indeed, other studies report that caffeine slow metabolizers can have up to a 64% increased risk of a heart attack depending on their caffeine dose.

Fortunately, less than 100 mg/day appears to be safe, even for caffeine slow metabolizers.  How much is 100 mg of caffeine?  A 100 mg dose of caffeine is approximately the equivalent of one cup of coffee, two cups of tea, three 12-ounce cans of soda pop, or four ounces of dark chocolate.

Why does medical science seem to be “flip flopping” on issues like coffee and caffeine?  This is likely because we have not taken into account genetic differences.  Just as everyone responds differently to medications, everyone responds differently to caffeine.

When it comes to caffeine metabolism, I am a slow metabolizer.  Fortunately, dark chocolate does not cause palpitations or arrhythmias for me.  While I love my dark chocolate, as a slow caffeine metabolizer, I must eat it first thing in the morning or I will have troubles sleeping at night.

The Big Picture

In the big picture of things, if you suffer from palpitations, arrhythmias, or heart problems should you or shouldn’t you consume caffeine?  Fortunately, this study suggests that if your caffeine source is coffee, tea, or chocolate you may be just fine.

One important thing to remember is that this study was just an average of 1,388 people.  I’m sure that of these 1,388 people, there were some whose heart’s were very sensitive to caffeine.  Perhaps these were the caffeine slow metabolizers?

While you could certainly have your genes tested to find out, as I described in a previous blog, perhaps an easier solution would be to just monitor how caffeine affects your body.  If caffeine causes palpitations or heart arrhythmias it would be best to avoid caffeine.  In contrast, if it doesn’t seem to bother you then it is probably OK unless your doctor tells you otherwise.

If you have heart problems or insomnia, try cutting out caffeine, or even setting a caffeine curfew of say 12 pm in the afternoon, to see if it makes a difference.  Perhaps you are like me in that caffeine is fine first thing in the morning.

How does caffeine affect you?  Please leave your comments below.  Also, if you have any questions about this article, please leave your questions below.  I will try to answer every question.

Disclaimer Policy: This website is intended to give general information and does not provide medical advice. This website does not create a doctor-patient relationship between you and Dr. John Day. If you have a medical problem, immediately contact your healthcare provider. Information on this website is not intended to diagnose or treat any condition. Dr. John Day is not responsible for any losses, damages or claims that may result from your medical decisions.

  1. Caffeine, milk chocolate speeds my heart beat up 30 beats a min, ,I havenen’t drank caffeine drinks for 2 yrs now,I was a chocololic until recently, I have mostly eaten dck choc most of my life. I noticed choc started giving me palpatations this past March, raised my bp, I was hospitalized 6 days. On sun I ate 1 milk choc covered pecan had A Fib for hrs. I have never smoked or drank alocohol, I was a dk choc sugar addic until March 2016, I am 78, ride a two wheeler 40 min each twice daily,so now no chocolate I guess. My dad’s family were all very sensitive to caffeine,made them depressed,I feel that is where my sensitivity comes from.

    • Hi Judy,

      Sorry to hear that you are sensitive to caffeine. Many of my patients share this same sensitivity.


  2. When I was in my early 30s, I had a job with free coffee and plenty of spare time. I drank about 10 cups of coffee per day and started having PVCs. My doctor told me to quit drinking coffee; I did; the PVCs went away. I now drink a cup (sometimes 2 cups) of coffee every day and do not have any PVCs.

  3. To am 63 years old, have suffered with PACs, then PVCs, and random bouts of AFIB since I was 35, healthy, and of normal weight. Avoided caffeine at all costs. However I found this past year that just one cup of caffeinated coffee every AM actually evens out and regulates my rhythm now! What I did find was that the oral calcium I was taking every day was increasing bouts of AFIB. I don’t take any calcium supplements anymore- which I had taken for many years. I will never take calcium again. All I take is 10 mg of propranolol at bedtime which also helps. But I was truly surprised about the caffeine actually strengthening the heartbeat and rhythm. I should also mention that I took mixed magnesium for some time but it actually made things much worse- rate so slow that the rhythm broke up. Quit that too- never again. Focused now also on low-sodium V8 for copious amounts potassium which also helps.

    • I’ve been living with relatively high load PVCs/PACs the last 4 years (I’m 34) and I’ve started to suspect that coffee in the morning evens out my heart rhythm. I cut back from two cups a day last year and the abnormal beats began to increase. But each morning after I have coffee I enjoy several hours of abnormal beat-free time. Could be related to other factors–I take a mineral/magnesium supplement in the morning–but it’s interesting.

      • Hi Aaron,

        It is entirely possible…everyone is different and what works for you may not work for someone else…


  4. Your article couldn’t be more timely! I am a Starbucks toting card holder. I receive stars every time I buy. 12 stars and I have any free item! I receive bonuses of free or discounted drinks mid day and evening… I have allowed myself an occasional extra trip to get a “bonus” more and of course mores .. Sugar free or loaded they are good. Stronger and more or less sweet. In review the campaign to increase sales is working. Fighting caffeine, sugar pick me up and the allure of “star collection”. Youre article was timed perfectly . A non caffeine eye opener.

    • Hi Terri, Mary, Nita, Bob, Sam, Anna, Marshall, Nancy, Helen, Richard, John, Betty, and Michael,

      Thank you so much for reading and commenting on this article!!! Hope I didn’t miss anyone else who left their comments.



  5. I never drank coffee and seldom drank a coke until age 28 when I started having headaches and found quick relief from drinking a coke. I soon found drinking one after 5 p.m. would keep me awake for most of the night. As I have aged, my caffeine cut-off time has become earlier and earlier so I don’t keep it in the house. Sometimes I just can’t resist an ice-cold fountain drink in the morning or with lunch. Just writing this has made me thirsty, but it is late at night and cold outside, so too bad, so sad!

  6. In my earlier 20s, I use to drink a lot of coffee. Many older people told me not to drink so much because the caffeine can cause more harm then good. Young and ignorant, I don’t listen. I used to drink at least 3 cups a day and sometimes out with friends at nigh and have a another cup of coffee or tea. I really didn’t notice much effect doing that age.
    when i got to my 30s. there was a few occasion where I started feeling very uncomfortable, more like i was getting sick all of a sudden. I was feeling Dizzy, I mean vertigo dizzy. I was very nauseous and actually vomited in a few times. I was weak and breathing heavily. I did not realize what was the cause, I know something was wrong, but don’t know the cause. it took a while for me to figure out every time I have this sensation, it was after I drink coffee. somehow I can no longer tolerate it any longer. so I completely stop drinking coffee and my issues caused by coffee has gone away.
    I can’t speak for other people, but I can tell you that caffeine does give me palpitation, fast racing heart and follow by other symptoms, dizziness, nauseous. lightheaded and more. My psychiatrist had me drinking coffee to bring my heart rate up just so I can feel the sensation. (She was working with me of the anxiety issue). and sure enough it does make my heart race. I also realize when I go to a restaurant and order some Chinese tea, it also give me the same sensation. I do believe caffeine does play a major part in heart palpitation.

    • to be on the safe side I have less than one half of coffee per day and have little or no chocolate and no soda. I was diagnosed with pac’s and an irregular heartbeat this year…but with diltizem 120….30 minutes walking every day and slight change of diet and stress maintenance – I am like 115/75 with heartbeats in the 60’s most of the time.
      I am 59. It could have been a one off year but why take chances….caffeine, chocolate, sugar and alcohol all new lows. Plus has CT angio to be safe and had 5 calcium score.
      So I am looking forward to my next treadmill, echo etc. thanks for your good advice…

  7. First time I ever had an attack of palpitations… I was 20 and had just drunk my first short black coffee… Wow!!!

  8. I noticed that the first time I experienced A-Fib was when I had unknowingly been drinking an orange/black licorice tea for several days. I had no idea that the tea contained a significant amount of caffeine and stimulants. I was just using it for a sore throat. Last November I went into A-Fib after I had consumed a large portion of Chocolate Ice Cream. I think that caffeine definitely played a role in both of these incidents. Since I also have a problem with insomnia I am now going to try limiting my chocolate intake at night. Thanks for the tip. I will let you know if it helps.

  9. Great info! As a lifelong arrhythmia patient (WPW and high load PVCs) and as a green tea and dark chocolate addict, I have noticed that sometimes caffeine seems to affect me and sometimes not. I did not know about the slow metabolizing gene, but think maybe that’s an issue with me. I have cut down from up to 6 cups of green tea a day and now restrict my tea intake to one cup of green or white tea before 3pm…limiting the chocolate is more difficult; I think it gives me a boost in the late afternoon. However, after reading your article I will be trying to keep the chocolate consumption before 3pm as well!

  10. Caffeine in chocolate seems to be a catalyst for heart arrhythmia and migraines if I eat a lot and I am under stress and perhaps a little dehydrated. In other words, if everything else is in order, I seem to be able to tolerate chocolate. But if stressed and then I add chocolate, the negative results can be immediate. I don’t drink caffinated drinks.