London researchers warn coffee could adversely affect blood pressure diagnosis and management

Researchers in London, Ontario have shown that your morning cup of coffee could be adversely affecting diagnosis and treatment for high blood pressure. The research team from Western University and Lawson Health Research Institute measured how occasional coffee consumption in individual patients impacted the action of calcium channel blockers, a commonly prescribed class of blood-pressure lowering medication.  

This comprehensive phase-one study published in the American Journal of Hypertension showed the combination of coffee plus a calcium channel blocker, felodipine, led to elevated blood pressure compared to felodipine alone, likely by blocking the beneficial effect of the drug at blood vessels. Calcium channel blockers relax and widen blood vessels, making it easier for blood to flow and in turn lower your blood pressure. 

“Even one cup of coffee containing a relatively low amount of caffeine remarkably compromised the anti-hypertensive effect of this drug at the maximum recommended dose,” said Dr. David Bailey, Lawson Scientist and researcher at Western’s Schulich School of Medicine & Dentistry. “If you wanted to overcome the effect of the coffee, you had to double the dose of this anti-hypertensive drug which could increase the risk of unwanted excessive drug effects, particularly during the period when coffee is not consumed.”

Previous studies have shown that coffee and caffeine don’t have much effect on blood pressure for those who drink coffee on a regular basis because of tolerance development. However, this study demonstrated that just two days abstaining from coffee was sufficient time to eliminate caffeine from the body and to increase blood pressure on subsequent coffee exposure.  Just one cup of coffee caused the maximum increase in blood pressure and it occurred by one hour after intake and lasted for several hours. 

“If you are an occasional coffee consumer and you have a cup of coffee twice or less a week, you have this risk of increased blood pressure which can be substantial in certain individuals,” Bailey said. “Occasional ingestion has been surveyed to occur in 15 to 20 per cent of the coffee consuming public.”

His worry is that if a patient consumes coffee just before seeing their doctor, diagnosis and treatment management could be complicated because of this acute increase in blood pressure and potential for additional over-prescription of antihypertensive drugs.

According to Bailey, national and international societies’ evidenced-based hypertension guidelines currently do not address the effect of coffee, likely because insufficient information. He hopes that this study will help inform and encourage further studies about issues associated with occasional coffee consumption.

“We want to raise awareness about the potential risks for the high number of people who are occasional coffee drinkers.” Bailey said.

The study was funded by the Heart & Stroke Foundation of Canada.