The text of this report is primarily based on the work of Catherine Fan, Sarah Langlois, Molly Meade, Indee Ratnayake, Justine Colvin and Jessica Mackay. They are students majoring in Medical Science on the Cambridge Tradition program.
Caffeine, a bitter, white crystalline xanthine alkaloid, acts as a central nervous system stimulant drug in the human body. It is commonly used in humans as a way to temporarily ward off drowsiness and restore alertness. Caffeine is found in the seeds, leaves and fruits of some plants. Caffeine serves as a natural pesticide for plants because of the effect it has on insects, inhibiting their ability to feed on the plant.
In the body, adenosine binds to adenosine receptors, decreasing cell activity. Caffeine competitively binds to adenosine receptors, which prevents the adenosine from binding, and in turn leads to increased neuron firing. Caffeine also constricts blood vessels in the brain. In response to increased neuron firing, the pituitary gland releases adrenaline, which in turn increases the heart rate. Previous studies suggest caffeine reaches peak plasma between 35-45 minutes after ingestion. This trial unravels if the caffeine content of Redbull has any clinical value in decreasing reaction times
The aim of this experiment is to explore the effects of a caffeine challenge equal to the dose present in a red bull on the reaction times, heart rates and blood pressure of Cambridge Tradition students aged 16-17 years of age in a randomised controlled trial
The class roster for the 2014 Medical Science class was randomised into two equally sized groups. The intervention group recieved 150 ml of orange juice with a caffeine concentration of 53.3 mg/100ml. The placebo group recieved 150 ml of orange juice with 80mg of glycolate. Glycolate is a tasteless, odorless disintegrant, which is available sterile and leaves a similar residue to dissolved caffeine.
All students took baseline heart rates, and reaction tests at baseline and around 45 minutes after intervention. For the reaction test, each student held their fingers over the 0 cm mark on a 30cm ruler, and measured where they caught it when released by another student. The test was taken in triplicate and the mean recorded. Reaction test results need to be converted to a temporal measure of reaction speed. We can convert the metres the ruler fell to time using , which equates to . A sub sample of 16 students also collected systolic and diastolic blood pressure using an automated cuff at baseline and around 45 minutes after intervention.
Tutors note: To enable the teaching of both cross-over and randomised medical trial design, students recieved both the placebo and intervention with a 24 hour washout period between each challenge. Repeated measures within individuals were not accounted for in the results.
46 students completed the trial, providing 75 observations. There were no loses to follow up. For 8 observations the student had taken a caffeinated beverage earlier that da
Table 1. Change in the two arms
|Outcome||Placebo group||Caffeine group|
|Reaction time (s)||-0.07||-0.22|
|Heart rate (bpm)||-1.2||2.9|
Table 1 indicates changes in HR, reaction time and BP occured in both the placebo and caffeine groups. Reaction time decreased in the caffeine group decreased to a greater degree than the placebo group, while HR and BP increased in the caffeine group.
Figure 1. Change in reaction time
Figure 1 shows the raw changes in reaction time for the two arms. The spread of observations was much greater in the caffeine group, and there was a stronger tendancy to a decrease in reaction time. Figure 1 also suggests that the raw change may not be an appropriate measure, and if we include the 95% confidence intervals of these values we may be better placed to understand whether a result is statistically significant.
Figure 2. Change in reaction time with 95% confidence intervals.
Figure 2 shows the spread with grey boxes which represent the 95%CI, which is the interval we believe has 95% confidence of including the true mean for each arm.