![]() The investigators who recorded the study participants’ blood pressure did not know which drink was caffeinated.Īfter randomisation, study participants completed a brief questionnaire about their sociodemographic data and personal history of hypertension. The randomisation list was created using the online Research Randomizer software, 10 and 110 codes (labelled as ‘A’ and ‘B’) were placed in opaque envelops, which were opened at enrolment. After obtaining informed consent, study participants were randomly assigned to either the intervention or control group. Eligible study participants were healthy male and female students aged >18 years and were free of chronic diseases, including hypertension. Medical students studying in the library were invited to participate. The drinks (labelled as ‘A’ and ‘B’ respectively) were freshly prepared by an investigator who was not involved in the subsequent part of the study.Ī quiet room in the IMU library was used for this study. The amount of caffeine received by the participants in the intervention group was approximately 1.4 mg/kg of body weight. The amount of caffeine in the intervention and placebo drinks was verified by a private laboratory (name available from the investigators) as 82.2 mg and undetectable, respectively. The instant coffee chosen consisted of the caffeinated and decaffeinated varieties of a popular brand available commercially. ![]() The drinks were made with two teaspoons of instant coffee (2.6 g), 250 ml of warm water and one packet each of non-dairy creamer and sugar. The intervention and placebo were standard coffee drinks (caffeinated and decaffeinated, respectively) in Styrofoam cups (250 ml). The study participants were medical students from the International Medical University (IMU) Clinical School in Seremban, Malaysia. Our study design was a randomised, double-blind, placebo-controlled clinical trial. 9 Thus, we think it is more useful to ascertain if a typical cup of coffee (with 80 mg of caffeine) can produce a significant hypertensive effect. 8 However, in the US, a standard 8-ounce (240 ml) cup of coffee contains around 100 mg of caffeine, whereas espresso has a much higher content of caffeine (240–720 mg per 8 ounces). 6 The Australia New Zealand Food Standards states that there is 80 mg of caffeine in a 250 ml cup of caffeinated beverage, whereas percolated coffee has 60–120 mg of caffeine per cup. On the other hand, a review by James estimated that dietary caffeine will raise mean population blood pressure by approximately 4/2 mmHg. ![]() ![]() In a review by Nurminen et al, 5 a single dose of caffeine (200–250 mg, equivalent to two to three cups of coffee) increased SBP by 3–14 mmHg and DBP by 4–13 mmHg in normotensive study participants. 4 Reviews of the hypertensive effect of acute consumption of coffee/caffeine highlighted the heterogeneity of study participants, dosage of caffeine and study designs. 3,4 Interestingly, the reviews identified a somewhat larger blood pressure elevating effect of caffeine versus coffee 3 and a greater effect among younger study participants. 1,2 Systematic reviews of randomised controlled trials on the chronic consumption of coffee/caffeine confirmed a small but statistically significant increase in systolic blood pressure (SBP 2.0–2.4 mmHg) and diastolic blood pressure (DBP 0.7–1.2 mmHg). The potentially deleterious effect of coffee intake on cardiovascular health has been a subject of research interest.
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