Coffee and tea come along with some amazing health benefits – primarily from their richness in antioxidants. However, you’ve probably heart that too much caffeine can be a bad thing and that it can be bad for your heart – increasing your heart rate and blood pressure. But what’s the science behind it? Does caffeine really cause high blood pressure?

Does Caffeine Really Raise Blood Pressure?

To really understand if caffeine really causes high blood pressure let’s take a bit of a deeper look on how caffeine really works. It’s no secret that caffeine is a psychostimulant that naturally occurs in the leaves of more than sixty different plants. Of the most popular plants, it’s found in coffee beans, cacao, guarana, and tea leaves (1). Most people get their caffeine consumption from either cofee, tea, or energy drinks such as Redbull or Rockstar.

Once caffeine is ingested, it start’s to have a direct effect on something called adenosine receptors (specifically adenosine A1, adenosine A2a, and adenosine A2b)(1).

How Adenosine Receptors Work

adenosine and caffeine

Adenosine causes a vascular smooth muscle relaxation which is what our blood vessels are made of. When our vessels are relaxed our blood pressure is lower.
In the heart, adenosine lowers heart rate and conduction of electrical impulses (chronotrophy and dromotrophy).

Adenosine is a chemical released by the body that has an effect on our blood vessels and also on our heart. When adenosine binds to type 2A receptors it changes our calcium and potassium levels inside our cells. It blocks calcium from entering our cells and it allows more potassium to come out of the cells. This process causes our blood vessels to open up wider and dilate. When our blood vessels are dilated and more open, blood has more space to fill and in theory, we can have lower blood pressure (1, 9, 10).

In our heart tissue, adenosine binds to A1 receptors. The A1 receptors in the heart have a direct effect on our pacemaker cells in are SA node (the hearts primary rhythm maker). It causes slowing of the conduction currents and decreases the rate at which our heart contracts. Adenosine can also block the release of norepinepherine – a hormone responsible in the body’s fight or flight response which increases heart rate and blood pressure (1,9,10).

In the emergency room setting, adenosine is frequently given for rapid heart rates. For you at home, it helps to regulate your heart rhythm and other cells.

What Does Caffeine Have To Do With Adenosine?

You might be wondering, why do we even care about adenosine? Caffeine competes with adenosine at the receptor sites. By reducing the amount of adenosine taking place at adenosine receptors, it causes the opposite of all things that adenosine can do – caffeine can cause a faster heart rate and blood vessel constriction which raises blood pressure (1).

But Does Caffeine Really Cause High Blood Pressure?

For a long time now doctors have been suggesting people to lay off caffeine because “caffeine can cause high blood pressure.” But what does the science really say?

According to several studies, including a review, meta-analysis and clinical research, caffeine may increase blood pressure (1). Emphasis on: caffeine may cause high blood pressure.

In theory, this is because of the direct effect that caffeine has on adenosine receptors in the body.

However, let’s dig further:

In human studies systolic, diastolic, and mean arterial blood pressures were elevated following caffeine intake (2). However, this study was done on eight people who performed physical activity (cycling) for sixty minutes. The subjects took 5mg/kg of caffeine and were compared with a group that only took a placebo.

However, what the researchers also found was that (in nine other studies) the hypertensive effect of caffeine typically goes away after about twenty-four hours (1).

The average half life of caffeine is about eight hours. Which means that out of all the caffeine that you take in, it takes about eight hours for half of it to leave your body. Which is the main reason that effects of caffeine tend to drop as twenty-four hours nears.

Other Notable Findings From These Studies:

Out of one meta analysis that looked at sixteen different studies with 1010 different people, the effects of coffee on blood pressure was looked at. What they found that was when caffeine was ingested through coffee as opposed to caffeine pills at about three cups of coffee a day – the effects on blood pressure were rather small. Coffee only raised the systolic (the top number) blood pressure 1.2mmHg and for diastolic (the bottom number) blood pressure it was 0.49 mmHG (6) – which is virtually nothing! The analysis also found that caffeine had no effect on heart rate (6). Another study which included two cups of Italian espresso and 200mg caffeine pills found that there was also no effect on heart rate (7).

Another study took 165 men and women from the ages of thirty-five to sixty-four and gave them 240mg of caffeine spaced throughout the day followed by a placebo controlled group. What they found was that the diastolic blood pressure increased by about 3mmHg – again a rather small increase (8).

Some obvious mentions about caffeine:

Stress causes a release of hormones that initiate our fight or flight response. Naturally this response causes our veins to constrict, heart rate to rise, and blood pressure to increase. Caffeine can add to the natural response of stress – but it might vary on individual (1).

Do Long Term Effects On Caffeine Raise Blood Pressure?

In humans, long-term consumption of coffee appears to lead to an adaptation response, with effects on blood pressure diminishing over time (3) . In a four week study, individuals were given eight cups of coffee which was the equivallent of about 504mg of caffeine. Within the first three to five days of coffee consumption, patients had an increased effect on blood pressure and heart rate. However, by the end of the four week period, the body seemed to have adapted and no longer was experiencing high blood pressure. All the individuals were healthy subjects.

In that same Italian study which had volunteers drink two cups of espresso and take an additional 200mg of caffeine through a pill, they found was that five volunteers in the study who drank on average of five cups of coffee a day had no change in their blood pressure – adding to the notion that over time, the body adapts to caffeine (7).

Two studies failed to show any relationship between caffeine and blood pressure at all (1). However, these studies should probably be looked at as a grain of salt seeing the overall act of caffeine on blood pressure and how it has an effect on adenosine receptors and also the majority of research showing the opposite.

So Does Caffeine Cause High Blood Pressure?

Even the American Heart Association states that the effect of caffeine on blood pressure appears to be mixed – it almost appears to vary on an individual basis and the body seems to get used to long term caffeine use (4).

Those individuals with risk factors for coronary artery disease: diabetes, uncontrolled high blood pressure, smoking, prior history of cardiac disease, and elevated stress, should keep daily caffeine consumption lower between one to two cups of coffee/day. They should also be aware of any symptoms that might come up after caffeine consumption such as heart palpitations or anxiety.

If you think that caffeine seems to be causing issues for you body, do the sensible thing, just don’t have any For the average person, it appears that caffeine at this point, has little very little to do with elevation of high blood pressure when taken in low to moderate amounts.

1. N.a. “Caffeine.” “Natural Standard – The Authority On Integrative Medicine.” 2015. Web. 13 July 2015.
2. Celik, S., Dorsey, J., Engels, H., Wirth, J. “Influence Of Caffeine On Metabolic and Cardiovascular Functions During Sustained Light Intensity Cycling and At Rest.” International Journal Of Sports Nutrition. 9 December 1999. Web. 13 July 2015.
3. Ammon, H., Bieck, P., Mandalaz, D., Verspohl. E. “Adaptation Of Blood Pressure To Continuous Heavy Drinking Coffee Drinking In Young Volunteers. A Double Blind Crossover Study.” British Journal Of Clinical Pharmacology. June 1983. Web. 13 July 2015.
4. N.a. “Caffeine and Heart Disease.” American Heart Association. 17 March 2014. Web. 13 July 2015.
5. James, J. “Critical Review Of Dietary Caffeine and Blood Pressure: A Relationship That Should Be Taken More Seriously.” Psychosomatic Medicine. January-February 2004. Web. 13 July 2015.
6. Arends, L., Geleijnse, J., Grobbee, D., Kok, F., Noordzij, M., Uiterwaal, C. “Blood Pressure Response To Chronic Intake Of Coffee and Caffeine: A Meta Analysis Of Randomized Controlled Trials.” Journal Of Hypertension. May 2005. Web. 13 July 2015.
7. Boni, M., Bongiovi, S., Casiglia, E., Colangeli, G., Paleari, C., Penzo, M., Pessina, A., Petucco, S. “Haemodynamic Effects Of Coffee and Caffeine In Normal Volunteers: A Placebo-Controlled Clinical Study.” Journal Of Internal Medicine. June 1991. Web. 13 July 2015.
8. Everson-Rose, S., Faraq, N., Lovallo, W., McKey, B., Vincent, A., Whitsett, T., Wilson, M. “Caffeine and Blood Pressure Response: Sex, Age, and Hormonal Status.” Journal Of Women’s Health. June 2010. Web. 13 July 2015.
9. Klabunde, R. “Adenosine.” Cardiovascular Pharmacology Concepts. 7 September 2012. Web. 13 July 2015.
10. N.a. “Adenosine.” Lexicomp. 14 July 2015. Web. 14 July 2015.