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Introduction Caffeine is a naturally occurring chemical stimulant Essay

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Paper type: Essay

Introduction

Caffeine is a naturally occurring chemical stimulant also called trimethylxanthine. Its

molecular shape is similar to adenosine’s – a chemical that can be found in all human cells. For

the brain, it works as a central nervous system depressant. In standard conditions, the chemical

prompts sleep and limits arousal by slowing down nerve function. Caffeine can bind to the

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brain’s adenosine receptors, however it doesn’t decrease cell’s activity, like adenosine does.

As caffeine takes up adenosine receptors, the brain can no longer sense adenosine, which makes

the cellular activity rise instead of going down [3]. This results in an increased blood pressure,

as the high cellular activity causes a greater demand for blood flow [1]. The Food and Drug

Administration (FDA) describes caffeine as both a drug and a food additive. In nature, caffeine

can be found in around 60 plant species, such as cocoa beans, kola nuts, tea leaves and coffee

beans. It is added to various soft drinks and is also a component of pharmacological

preparations and over-the-counter medicines including analgesics, diet-aids, and cold/flu

remedies.

It is commonly known that one can benefit from regular intake of caffeine in many ways, for example improving their mental alertness, sports performance, slowing down their mental decline and more, however it can cause a lot of harm. Among many, it may induce high blood pressure (also known as hypertension). High blood pressure is a condition that causes a person to have their arteries’ walls to receive too much pressure continuously – 140/90mmHg or more [8].

In my investigation I am going to investigate the short term effect of caffeine intake on blood pressure in a group of regular coffee drinkers.

Furthermore, coffee is the most common source of alkanoid for the majority of my society – it is consumed regularly by 75% of it [2].

Research Question: What is the influence of caffeine on teenagers’ blood pressure? Hypothesis

Results of my biological investigation should be the following:

– Caffeinated coffee increases the blood pressure more than decaffeinated coffee.

Variables

Independent Variable: Presence of caffeine in a beverage

Dependent Variable: Blood pressure, measured by the sphygmomanometer in mmHg [± 0.5mmHg]

I chose this topic, because I am a regular coffee drinker myself. I have been drinking coffee for

over two years and I have not noticed any negative effects of it. However I keep hearing very

mixed opinions about the possible outcomes of drinking coffee. The thing I would hear the most

often, was always coffee’s negative effect on blood pressure. That is why in my experiment I

would like to find out if that really is the case.

1

Controlled Variables:

• Amount of coffee – Every participant is going to get 10 grams [± 0.001g] of coffee,

measured by the electronic mass balance. If the amounts differed between participants the results could be significantly altered too.

• Amount of water – Every beverage is going to be 200 mL [±0.5mL], measured by a scale. If there was too little water, coffee would not fully dissolve, hence influencing participants’ overall caffeine intake and blood pressure levels.

• Beverage’s temperature – Every beverage is going to brewed using boiling water and then cooled down to be slightly above the room’s temperature (up to 40°C [±1]). If the drinks were too hot participants could hurt themselves trying to drink them.

• Participant’s age – I am aiming at finding the effect of caffeine on teenagers, therefore I will be taking measurements people aged 16-19. However, there could be some age- specific differences in the human blood pressure levels, which could result in various results without any real correlation.

• Coffee Brand – Both of the coffees used, caffeinated and decaffeinated, were from the brand Nestle. Other brands may possess more caffeine or other substances which may affect blood pressure. Thus, the results of the experiment may only apply to this specific coffee mix.

Measured but not controlled:

• Dates of taking the measurements – I am going to meet with participants on the dates

that suit them best, therefore I cannot control the amount of time between sessions. There could be some differences in the atmospheric pressure, which can affect participants’ blood pressure.

• Participants’ sex – The effect of caffeine intake on blood pressure may differ among sexes, however due to a limited sample pool I am not able to create a division between males and females.

• Temperature of the room where the measurements are taken – The temperature of the surrounding could have an effect on the sample’s blood pressure, thus making the readings unreliable.

2

Methodology

Materials: Thermal plastic cups, coffee Nestle, decaffeinated coffee Nestle, sphygmomanometer [±0.5mmHg], kettle, electronic mass balance [±0.001g], 250mL beaker [±10mL], thermometer [±1°C]

1. Find 20 people, who consume caffeine regularly, and assign them numbers for the purpose of confidentiality.

2. Debrief the sample about the purpose of the experiment, the way it is going to be carried out, their rights of withdrawal and confidentiality.

3. Ask each person to give their written consent for participation.

4. Take 3 persons at a time – They can’t have drunk coffee that day before the

measurements.

5. Prepare 3 beverages of either regular or a decaffeinated coffee using the procedure:

measure 10g of the substance, using the electric mass balance, and mix it with 200mL

of water, measured using the beaker, in a thermal plastic cup.

6. Measure their blood pressure, using the sphygmomanometer, and write it down next to

their number.

7. Give each participant the beverage, without them knowing what type of coffee it is.

Make sure it’s temperature does not exceed 40°C, by using a thermometer [±1°C].

8. Wait 40 minutes.

9. Measure their blood pressure again.

10. On a different day ask the person to drink the coffee (the other type) again, along the

same procedure.

11. Repeat until all 20 people have already been tested after drinking the regular and

decaffeinated beverage.

Safety Issues

? No participants were hurt throughout the experiment.

? All participants are regular coffee drinkers, to avoid any sort of a caffeine intake shock

which may occur once a person is not accustomed to the substance.

? The coffees used in the experiment, are standard coffees that anybody can buy in a

supermarket.

? Every participant was informed about their rights and the purpose of experiment.

? The temperature of the beverages was up to 40°C, therefore no participant could harm

themselves by taking part in the experiment.

3

Environmental Issues

In my experiment there were no environmental issues.

Raw Data

Qualitative Data:

Caffeine may have affected distinct individuals differently. Certain participants appeared more stressed and active after indulging the caffeinated beverages, while others were more sleepy and calm. There was also a number of participants who did not exhibit any conspicuous reactions to the beverage.

Quantitative Data:

Table 1. Systolic and diastolic blood pressure measured in mmHg [±0.5mmHg].

Caffeinated

diastolic pressure

systolic pressure

Decaffeinated

diastolic pressure

systolic pressure

Participant Before After Before

1 71 81 121

2 79 67 125

3 59 60 103

4 81 82 122

5 91 79 151

6 83 90 126

7 72 74 114

8 82 70 127

9 80 83 113

10 83 85 130

11 71 67 112

12 79 63 128

13 80 67 127

14 63 71 101

15 77 89 122

16 74 78 119

17 63 70 109

18 88 95 119

19 70 80 119

20 60 60 108

Mean 75.3 75.6 120.0 SD 9.06 10.20 11.10

After Before

120 85

108 66

102 65

124 87

127 76

136 77

126 81

124 84

120 78

135 90

106 55

114 81

114 59

100 55

130 64

129 69

120 67

129 62

130 67

120 65 121.0 71.7 10.50 10.80

After Before After

82 124 113 68 103 102 63 105 100 87 134 135 73 121 132 72 126 122 89 134 142 85 133 133 75 114 114 76 136 128 62 97 110 57 136 110 58 98 101 52 98 95

66 102 103 74 114 118 80 116 134 93 96 129 73 121 132 74 109 111 73.0 116.0 118.0 11.10 14.30 14.20

4

Mean – Calculated using the formula: ?? = ??

?

?? – sum of all results

? – number of distinct pieces of data

Example of calculation:

71+79+59+81+91+83+72+82+80+83+71 +79+80+63+77+74+63+88+70+60

20

?? =

?? = 75.3

SD – Standard Deviation is a measure of average variance among

the pieces of data and the mean. It is important to calculate it to see whether the pieces of data

have similar values (small SD) or if they are extremely different (great SD) [7].

Standard Deviation was calculated using this formula:

Where:

? ? ?????? ?? ???? ??????

?? ? ?h? ???? ?? ?h? ?1

? ? ???h ?? ?h? ?????? ?? ?h? ????

? ? ????? “sum of”

? ? ?h? ???????? ?????????? ?? ? ??????

? = ??(? ? ??)2 ??1

Example of calculation:

(71?75.3)2 +(79?75.3)2 +(59?75.3)2 +(81?75.3)2 +(91?75.3)2 +(83?75.3)2 +(72?75.3)2 ?+(60 ? 75.3)2(80 ? 75.3)2 + (63 ? 75.3)2 + (82 ? 75.3)2 + (77 ? 75.3)2 + (74 ? 75.3)2 + (63 ? 75.3)2 +

? = (88?75.3)2 +(70?75.3)2 +(71?75.9)2 +(79?75.3)2 19

? = 9.0

5

Data processing

Figure 1. Blood pressure values.

140 120 100

80

60 73 40

20

0

16

DD2 DS1 DS2

120

121

118

5.

1

75.6

73

71.7

CD1 CD2 CS1

CS2 DD1

Where:

CD1 – Caffeinated coffee, diastolic pressure before drinking the beverage

CD2 – Caffeinated coffee, diastolic pressure 40min after drinking the beverage

CS1 – Caffeinated coffee, systolic pressure before drinking the beverage

CS2 – Caffeinated coffee, systolic pressure 40min after drinking the beverage

DD1 – Decaffeinated coffee, diastolic pressure before drinking the beverage

DD2 – Decaffeinated coffee, diastolic pressure 40min after drinking the beverage

DS1- Decaffeinated coffee, systolic pressure before drinking the beverage

DS2 – Decaffeinated coffee, systolic pressure 40min after drinking the beverage

In each case, there has been an increase in blood pressure. It can be noticed that in the case of

caffeinated coffee there has been a mean increase in diastolic blood pressure of 0.3 mmHg and

1 mmHg in systolic blood pressure, 40min after drinking the beverage. What’s surprising, in

case of decaffeinated coffee the mean increases in both types of blood pressure have been

greater. The mean increase in diastolic blood pressure was 1.3 mmHg, while the mean increase

in the systolic blood pressure was 2 mmHg. Moreover, the standard deviation values, in every

trial, are extremely similar before and after drinking a beverage. In the case of caffeinated

coffee, the difference in the standard deviation values of the diastolic blood pressure, before

and after drinking the beverage, was 1.14, while in the systolic blood pressure it was just 0.20.

When it comes to the decaffeinated coffee, the difference in the standard deviation values of

the diastolic blood pressure, before and after drinking the beverage, was 0.30, and in the

systolic blood pressure it was 0.10. Which means that there’s very little variance among the

average results, and thus the values obtained are similar.

6

Blood pressure [±0.05 mmHg]

Figure 2. Percentage increase in blood pressure.

Percentage Increase in blood pressure

2

1.5

1

0.5

0

Type of blood pressure and presence of caffeine

CD DD CS DS

Where:

CD – Mean percentage increase in the diastolic blood pressure, 40 minutes after drinking the

caffeinated beverage

DD – Mean percentage increase in the diastolic blood pressure, 40 minutes after drinking the

decaffeinated beverage

CS – Mean percentage increase in the systolic blood pressure, 40 minutes after drinking the

caffeinated beverage

DS – Mean percentage increase in the systolic blood pressure, 40 minutes after drinking the

decaffeinated beverage.

The mean percentage increase in case of the diastolic heart pressure was 0.4 in case of

caffeinated coffee and 1.8 in case of decaffeinated coffee. Furthermore, the value of the mean

percentage increase in case of the systolic heart pressure was 0.8 in case of caffeinated coffee

and 1.7 in case of decaffeinated coffee. Thus, it can be noticed that the mean percentage

increase in case of the decaffeinated beverages was significantly higher, than those of the

caffeinated drinks.

T-test

T-test is any statistical hypothesis which is used when comparing two sets of normally

distributed data. It shows the degree of overlap between the sets. The more overlap there is, the

more likely the pieces of data are the same. Where a small value of t indicates that there is little

to none difference between the sets. The value of t is compared against the appropriate number

in the table of critical values. In order to search for the right place in the table, the degrees of

freedom (DF) are calculated. If t is greater or equal to the critical value, then you can assume

that there is a statistical difference between the pieces of data. Furthermore, in biology the t

value at 0.05 is taken [6].

7

Percentage increase

?? = ?1 + ?2 ? 2

Where:

?? – number of terms in the set number 1 ?? – number of terms in the set number 2 Figure 3. T-test for the diastolic blood pressure for the diastolic blood pressure.

Calculation of the value of t:

? = 3.15? 0.8 +89 ?65 20

20 ? = 5.61

8

Figure 4. T – test for the systolic blood pressure.

Calculation of the value of t:

?=

0.9 ? 3.2 + 142

?118 20 20

? = 2.11

Calculation of the degrees of freedom (DF)

?? = 20 + 20 ? 2 = 38

9

Figure 5. T-test values [5].

The value of t at 38 degrees of freedom is 2.0244 (fig 5.). Both of the results calculated

previously (

5.61

and 2.11) are greater than this value. Thus, there is a statistically significant

difference between the increase in blood pressure, both diastolic and systolic. However, it does

not confirm the hypothesis directly as the increases were significantly higher in the case of

decaffeinated beverages than in the caffeinated ones – which is exactly opposite to what the

hypothesis claims.

CONCLUSION

Ultimately, it can be concluded that caffeine increases blood pressure in teenagers. However,

the results of my experiment suggest that caffeinated coffee does not increase blood pressure,

in teenagers, more than decaffeinated coffee does. Furthermore, it is the decaffeinated coffee

that caused the significant blood pressure increase, determined through the t-test. This is

exactly opposite to what the hypothesis claims. Even though placebo, which is the only factor

that could have caused the increase in blood pressure for the decaffeinated beverages, is known

to an extremely powerful effect, it was present in both types of beverages as the sample was

not informed which one they were receiving.

After conducting further research on decaffeinated coffee, I have found out that decaffeinated

coffee does seem to have an effect on human blood pressure, in adults. This research was

conducted by Smits et al. in 1989. In the study blood pressure was measured, over a period of

a total of 12 weeks, when participants were given caffeinated or decaffeinated coffee daily (6

weeks each type). Its results indicate that there is only a slight difference between the effects

of the two types of coffee [10]. However, this research differs slightly from mine. Not only is

the sample different, but also the amount of coffee and number of measurements. On the other

hand, the phenomenon of caffeine tolerance might have occurred. This effect claims that one’s

body can become to numb to the effect of this substance. Only people who either never ingested

caffeine or have abstained from it for a long period of time, can experience its full effects [9].

Thus, regular coffee drinkers may have already developed immunity to coffee and that’s why,

in the experiment conducted by Smits et al. there is little difference between the two conditions.

The other reference literature chosen does not provide data on the decaffeinated coffee intake,

however it is a meta-analysis of a large number of studies on caffeine, conducted by Mesas et

al. in 2011 [6]. In 5 trials, the intake of 200-300mg of caffeine (equivalent of 10g of Nestle

10

coffee) resulted in a mean increase of 8.1mmHg in systolic blood pressure, and 5.7 mmHg in

diastolic blood pressure, while in my experiment it was 1 mmHg and 0.3 mmHg respectively.

Further, the measurements were taken in the first hour after the beverage intake, which is

similar to my experiment’s procedure. The greatest difference however, was that the

participants knew that they are getting a caffeinated beverage each time, and thus the placebo

effect could be stronger since the sample is expecting to have their blood pressure increased.

The conspicuous difference, which is present between the results that the literature suggests

and the ones I have obtained, could be the effect of the presence of certain limitations that flaw

the reliability of my results:

Table 2. Limitations and improvements for the experiment.

Limitation

Between Measurements

Improvement

Different Conditions

Participants were not isolated from the surrounding between measurements, which could have resulted in external factors, such as stress, affect their blood pressure. Thus, participants should be isolated from the environment between the

measurements

Different External

Conditions

and Females

Barometric pressure fluctuates among distinct days, further it is a common factor affecting people’s blood pressures [4]. Therefore, all measurements should have been taken on the

Not All Qualitative Data

Recorded

same day.

A number of other factors could have played a role on human blood pressure fluctuations, such as stress. Thus, an interview should be conducted before each measurement in order to

No Division Between Males

access its reliability.

The effects of caffeine may vary between sexes. It is an important factor to consider, when trying to determine the effect of caffeine on human blood pressure. Thus, there should be a division between males and females, when it

comes to analysing the results.

Diet Was Not Recorded

Besides not drinking caffeinated drinks, no dietary restrictions were placed upon participants. As mentioned in the introduction, caffeine is present in a great deal of foods, some of each could have been eaten by the participants on the day when their measurements were taken. Therefore, diet of each participants, on the testing day, should be recorded and

Participants’ Mass

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