Effect of Coffee Temperature On Blood Pressure-Abstract


Taylor Wessel, Jenny Yang and Katie Weiss


CU Boulder, Fall 2006


         As CU students, there are two things always on our minds: health and grades.  Being the Boulderites that we are, health is a very important aspect to our daily lives; however, as college students in this day and age, being able to stay awake into the wee hours of the night to study for Biology is also crucial. Therefore, we came up with the idea of testing the effects of coffee (a fundamental study tool) on blood pressure (a fairly good indication of general health).  Given the fact that a majority of college students drink massive amounts of coffee, especially around finals times, we wanted to test if coffee consumed for winter finals (hot coffee) had a different effect on blood pressure than coffee consumed during spring finals (cold coffee). 

         Coffee contains caffeine, which is a stimulant. Stimulants are drugs that "tend to increase alertness and physical activity"(1).  According to a teen health website, caffeine    "stimulates the central nervous system, causing increased heart rate and alertness"(2).  Due to the fact that caffeine increases heart rate, caffeine should also increase blood pressure.  But would hot and cold coffee have different effects?  Since the body would need to "heat up" the coffee by pumping blood at a faster speed, we hypothesize that cold coffee would have a more substantial effect on blood pressure that hot coffee. 

         In order to test our hypothesis, we looked at three female subjects with different consumption habits.  Our group consisted of one person who drinks coffee on a daily basis (Taylor), one who consumes on a weekly basis (Jenny), and a coffee virgin (Katie).  Each subject consumed an identical hot and iced Starbucks coffee drink on day 1 and day 2 respectively.  On day one, we measured each girl's blood pressure several times before, during, and after each subject consumed a hot 12oz. tall double shot skim vanilla latte from Starbucks. We obtained blood pressure measurements using a digital American Heart Association blood pressure machine located in the King Soopers on 30th and Arapahoe in Boulder, Colorado. Measurements were recorded before, 5, 10, 15, 20, and 25 minutes after beginning to drink. Each subject finished her drink by 15 minutes after.  On day two, the effects of an iced version of the exact same drink were tested under the same conditions. 

         Once we obtained our data, we used Microsoft Excel to visually depict our results and then statistically analyzed them.  After consuming hot coffee, the average systolic blood pressure was 106.1 mm Hg and the average diastolic blood pressure was 57.1; after consuming cold coffee, the average systolic blood pressure was 106.4 mm Hg and the average diastolic blood pressure was 62.9 mm Hg.  A paired t-test was used to compare average systolic blood pressures for hot versus cold coffee and to compare average diastolic blood pressures for hot versus cold coffee.  We combined the blood pressure measurements for all three students and then compared hot coffee data to cold coffee data.  For systolic pressure the p-value for hot coffee versus cold coffee was 0.441.  And for diastolic pressure the p-value for hot coffee versus cold coffee was 0.002.  Therefore, for systolic blood pressure, we were unable to reject the null hypothesis that coffee temperature was correlated with blood pressure.  As for the diastolic blood pressure, we were able to reject the null hypothesis and conclude that cold coffee significantly increased blood pressure compared to the effects of hot coffee.

There was a similar experiment conducted involving the effects of chocolate as an aphrodisiac on blood pressure.  They concluded that certain types of chocolate while others did not, gave results similar to ours.  Possible sources of error in our experiment included other food and drinks in the system that could have possibly affected metabolism rates, amount of coffee consumed during each time interval, and any differences in lifestyle and general health among the three subjects.  We could improve upon this study by testing more subjects (male and female) for a whole month's time and regulate their coffee intake to decrease the amount of uncontrolled variables.  We could also compare the effects of different temperature coffee between males and females.  Finally, we could test the effects of a wider variety of coffee temperatures.  


Works Cited


Division of Alcohol and Drug Abuse



2.       Caffeine