That extra cup of joe in the morning may help you feel more alert, but depending on your tolerance to caffeine, it could also cause a spike in your blood pressure.
Led by Dr. Noha H. Farag, a team of researchers at the University of Oklahoma Health Sciences Center in Oklahoma City set out to determine the effect of extra caffeine on people with "high" and "low" tolerance to the stimulant. Tolerance was established based on blood pressure response to a boost in caffeine during a previous trial.
In the continuation study, 85 participants were given varying doses of caffeine and had their blood pressure monitored through the day for a period of four weeks. Each week, participants received either 300 mg or 600 mg of caffeine a day or a placebo, each in three doses. On the 6th day of each week, subjects received an extra boost of caffeine - a total of 750 mg, which is the equivalent of about 5.5 cups of regular brewed coffee or 8 cups of instant - or a placebo, and monitored for any extra boost in blood pressure.
Both the low- and high-tolerance groups showed a spike in blood pressure when they consumed caffeine on the 6th day after taking the caffeine placebo for 5 days. But after they consumed caffeine throughout the week, only the low-tolerance participants showed an increase in blood pressure when they consumed extra caffeine on the 6th day.
The authors concluded that these results suggest the "clinical significance" of the effect of caffeine on some coffee drinkers.
Dr. Farag's study, which was published in the American Journal of Hypertension, was conducted in a laboratory setting, and the author notes that in real life, determining one's tolerance to caffeine is not such an easy task. As a result, he advises that people with high blood pressure or who are at risk for high blood pressure limit their caffeine intake.
Risk factors for high blood pressure include age, family history, diabetes, obesity, stress, and smoking. Having high blood pressure can significantly increase your risk of stroke and heart attack, though reducing blood pressure through diet, exercise and, if necessary, medication, can lower the risk.
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