Blood Pressure Response to the "Second Cup of Coffee" IRIS B. GOLDSTEIN, PHD, DAVID SHAPIRO, PHD, KA KIT HUI, MD, AND JUN LIANG YU, MD Twenty young male coffee-drinkers consumed 150 mg of caffeine in decaffeinated coffee three times a day for 8 days. On days 3. 4, 7, and 8, caffeine or a placebo was administered in the laboratory at 11 A.M., 8 A.M., 11 A.M., and 8 A.M., respectively, in a randomized double-blind crossover design. There was a blood pressure increase relative to the placebo 45 min after taking caffeine at 8 A.M. (5.8/6.5 mm Hg) An increase of 2.4/5.2 mm Hg was seen with the second cup of coffee at 11 A.M. The lower the subject's pre-coffee serum caffeine level, the higher the systolic response, both at 8 A.M. (r = -0.60) and at 11 A.M. (r = -0.62). Because of the prossor effect resulting from habitual caffeine intake, the adverse implications of caffeine use should be considered.
INTRODUCTION
Because of the widespread use of caffeine in the general population (1), there is considerable concern about its possible role in heart disease and hypertension (see review by Ernster (2)). If one looks at the acute effects of caffeine on blood pressure, there is general agreement that both systolic and diastolic blood pressure can be increased substantially for at least a few hours. The caffeine equivalent of two to three cups of coffee was reported to increase the pressor response in healthy, non-coffee-drinking adults (3-5) and in healthy coffee or tea drinkers who had abstained from caffeine for 9-24 hours (6-
From the Department of Psychiatry and Biobehavioral Sciences. University of California, Los Angeles (1 B.G.. D.S.), and the Division of Clinical Pharmacology. University of California School of Medicine, Los Angeles (K.K.H., J.L.Y.). Address reprint requests to: Iris B. Goldstein. Ph.D., Department of Psychiatry. UCLA, 760 Westwood Plaza, Los Angeles. CA 90024-1759. Received August 21, 1989; revision received November 27, 1989.
Psychosomatic Medicine 52:337-345 (1990) OO33-3174/9O/S2O2-O337SO2 00/0 Copyright © 1990 by the American Psycho
8). While there is little question that caffeine can elevate blood pressure acutely, some studies indicate that tolerance develops with habitual caffeine use, resulting in the cessation of pressor responses to caffeine ingestion. The clearest evidence comes from a study by Robertson et al. (9), who showed that after the third day of consuming 250 mg of caffeine, three times a day, there were no longterm effects of caffeine on blood pressure. Although there was no control of coffee intake, Ammon et al. (10) also showed that regular ingestion of coffee (504 mg per day) no longer affected blood pressure after day 5. The acute effects of caffeine on blood pressure are related to the pattern of caffeine use and the amount of caffeine regularly consumed. Many studies indicate that typical coffee and tea drinkers show a pressor response after overnight abstinence (9-12 hours) (6-8, 11-13). These pressor effects are also dependent on basal plasma caffeine concentration. Individuals who exhibited a short caffeine plasma half-life had low plasma caffeine levels after normal overnight abstinence from caffeine. As a result, the morning 337
GOLDSTEIN et al. cup of coffee elicited a pressor response despite the phenomenon of adaptation (14). The purpose of the present investigation was to look at the effects of repeated caffeine intake on blood pressure in a group of healthy, normotensive young male coffee-drinkers who were given prescribed amounts of caffeine to be taken daily throughout the study. Subjects were asked to take 150 mg of caffeine (the equivalent of two cups of instant or one cup of drip coffee) (15), three times a day, a dose level and pattern of usage simulating normal coffee-drinking. The study focuses on the initial morning blood pressure reaction to caffeine after 12 hours of abstinence, as well as the mid-morning response to the second cup of coffee a few hours later. In addition, serum caffeine levels were obtained to determine the relationship between the caffeine concentration in the blood and the pressor response. The study employed a randomized double-blind crossover design.
Procedures
Subjects were asked to consume standardized amounts of caffeine during the period of the study (8 days). They were supplied with prepackaged individual servings of decaffeinated coffee and 150-mg capsules of caffeine, and instructed to combine the contents of a caffeine capsule and the coffee packet in a cup of hot water. In trying to approximate normal coffee-drinking habits, we told the subjects to drink the coffee with breakfast. 1 hour before lunch, and with dinner. If dinner was going to be later than 6 P.M., subjects were to drink their last cup of coffee between 5 and 6 P.M. No other sources of caffeine were to be consumed. In order to increase compliance, subjects were told that blood samples would be drawn during each laboratory session in order to determine the amount of caffeine that had been consumed. During the week that the subject was maintaining his coffee schedule of three cups per day, he came into the laboratory on four different sessions. On these occasions the coffee was consumed in the laboratory rather than at home or at work. After the subject had been drinking coffee for 2 days, on the third day he had a cup of coffee with a light breakfast and reported to the laboratory for Session I at 1 hour before his usual lunch time (about 11 A.M.). The subject returned to the laboratory the following morning at 8 A.M. (Session 2). after not having smoked or consumed anything except water during the preceding 12 hours. Three days later he came back to the laboratory before lunch (Session 3) and again on the following morning (Session 4), as in the prior two sessions (Fig. 1). The laboratory sessions METHODS were held on four separate days, so that each session would be uncontaminated by any other laboratory session. In this way subjects could be studied on as typical a coffee-drinking schedule as possible. Subjects The subject was given coffee in the laboratory during all four occasions in a randomized doubleTwenty healthy white males between the ages of blind procedure. Sessions were each counterbal18 and 35 years (mean = 25) participated in the anced so that every subject received 150 mg of study. They signed a consent form approved by the caffeine in one morning session and a placebo in the UCLA Human Subject Protection Committee. Partic- other, combined with decaffeinated coffee. The ipation was confined to individuals who were regu- same counterbalancing occurred for mid-morning lar coffee drinkers. Caffeine content of each subject's sessions. To make certain that a subject always rediet was determined from individual self-reports ceived 150 mg of caffeine three times a day, he was (15). Daily caffeine intake of subjects ranged from 84 always given a second cup of coffee before leaving to 830 mg (mean = 338.8 mg). Anyone taking medi- the laboratory. If the subject received caffeine durcations or involved in any kind of medical treatment ing the test session, he was given coffee with a was excluded. Most of the men were non-smokers, placebo at the end of the session. If, on the other except for four subjects who smoked occasionally hand, this was a placebo session, he would be given (less than one pack per month). caffeinated coffee before he left. Subsequent ques338
Psychosomatic Medicine 52:337-345 (1990)
BLOOD PRESSURE RESPONSE TO COFFEE
DAY
1
2
3
4
5
6
7
LAB
8:00 AM
CAFFEINE
CAFFEINE
CAFFEINE
CAFFEINE
CAFFEINE
LAB
11:00 AM
CAFFEINE
CAFFEINE
5:00 PM
CAFFEINE
CAFFEINE
CAFFEINE
'IRCEBO
LAB CAFFEINE
CAFFEINE
8 LAB
CAFFEINE
CAFFEINE
CAFFENE CAFFEINE CAFFEINE
CAFFEINE
CAFFENE
CAFFEINE
Fig. 1. The schedule of caffeine consumption during the study, whereby subjects drank 150 mg of caffeine at home three times a day. Exceptions to this were laboratory sessions on days 3 and 7 at 11 A.M. and days 4 and 8 at 8 A.M. On these days subjects received either caffeine or placebo in the laboratory, counterbalanced.
tioning revealed that subjects were unable to discriminate between the caffeine and the placebo sessions. Except for the administration of either caffeine or placebo, all of the sessions were the same. After the subject sat quietly for 10 minutes, six blood pressure measurements were obtained with a Baumanometer mercury column sphygmomanometer, with a 1-minute delay between each measurement, according to the guidelines of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (16). Two radial pulse determinations (30 seconds each) were also taken. The average of the last five blood pressure readings and the two pulse readings were used in later analyses. All blood pressure and heart rate measurements were made by one of the authors (I. B. G.). Blood was drawn from the antecubital vein to determine serum concentrations of caffeine, which were analyzed with a reverse phase high performance liquid chromatography method (17). The subject was given 5 minutes to drink a cup of coffee. On the first 2 days he completed each of two halves of a detailed questionnaire on caffeine intake (18). The subject then sat quietly reading magazines. Because peak plasma levels for caffeine are generally reached within 15 to 45 minutes after ingestion (19) and peak blood pressure is reached at 60 minutes (3), we waited 45 minutes before taking final blood pressures. At that
Psychosomatic Medicine 52:337-345 (1990)
time two additional pulse and six blood pressure measurements were recorded, followed by a second blood draw. The subject drank a second cup of coffee (placebo or caffeine) and left the laboratory.
Statistical Analyses A repeated measures two-way within-subject analysis of variance (ANOVA) was computed on precoffee levels of systolic blood pressure, diastolic blood pressure, heart rate, and serum caffeine for time of day (8 A.M., 11 A.M.) x coffee condition (caffeine, placebo), and a similar ANOVA on the difference between pre- and post-coffee values was performed for each of the above variables. In order to determine whether the effects of caffeine were consistent over time, subjects given caffeine at 11 A.M. on day 3 were compared with subjects given caffeine at 11 A.M. on day 7. This was done by dividing subjects into two groups in a betweensubject ( test of post- minus pre-caffeine measures of heart rate, systolic blood pressure, diastolic blood pressure, and serum caffeine levels. Similar ( tests were run comparing the effects of 8 A.M. doses of caffeine given on day 4 as compared with day 8. Pearson r correlations were computed to determine the relationship between caffeine usage, blood pressure values, and serum caffeine levels.
339
GOLDSTEIN et al.
RESULTS
Placebo-Caffeine Differences The placebo-caffeine difference was Pre-Coffee Values significant for systolic blood pressure Pre-/Post-Coffee values (placebo or caf- [F(l/19) = 18.0, p < 0.0001] and for diafeine) for all measures are shown in Table stolic blood pressure [F(l/19) = 31.9, p < 1. There were no significant differences 0.0001], but not for heart rate. The caffeine in subjects' blood pressure or heart rate blood pressure change relative to the plaprior to drinking coffee for time of day or cebo was 5.8/6.5 mm Hg in the early coffee condition (placebo versus caffeine). morning (8 A.M.) and 2.4/5.2 mm Hg at Pre-coffee serum caffeine levels were sig- mid-morning (11 A.M.). A somewhat nificantly higher at the 11 A.M. session lesser effect for systolic blood pressure than at the 8 A.M. session [F(l/19) = 38.1, during mid-morning was indicated by a p < 0.0001]. The mean pre-coffee levels, placebo-caffeine interaction that was staaveraged for the caffeine and placebo con- tistically close to significance (p = 0.052). ditions, were 1.02 fig/ml at 8 A.M. and 2.0 Serum caffeine levels were significantly /ug/ml at 11 A.M. Although the level of higher after ingesting the caffeine as compre-coffee serum caffeine was higher at pared to the placebo [F(l/19) = 225.8, p < 11 A.M. than at 8 A.M., there were no 0.0001]. Relative to the placebo, serum associated differences in the pre-coffee caffeine levels increased in the caffeine blood pressure or heart rate. In spite of condition by 2.21 jug/ml in the 8 A.M. the blood pressure elevating effect of caf- session and 2.48 jug/ml in the 11 A.M. feine that had occurred early in the morn- session. There was no time of day effect. ing, this effect was not seen at the 11 A.M. Systolic blood pressure, diastolic blood session. pressure, heart rate, and serum caffeine TABLE 1.
Pre- and Post-Coffee Systolic and Diastolic Blood Pressure, Heart Rate, and Serum Caffeine Levels" 11 A M .
8 A.M. Pre Systolic BP (mm Hg) Caffeine Placebo Diastolic BP (mm Hg) Caffeine Placebo Heart Rate (bpm) Caffeine Placebo Scrum Caffeine (Mg/ml) Caffeine Placebo
Post
Pre
Post
115 1 (7.9) 117.0(7.8)
118.2 (9.4)'1 114 3(9.7)
116.4 (6.8) 116.6 (9.0)
116.2 (8 7)c 114.0(8.6)
74.2 (6.0) 75.7(6.3)
79.7 (4.7)fc 74.7 (5.6)
74.0 (8.3) 75.6 (6.4)
78.7 (7.0)" 75 1 (7 3)
66.6 (11.4) 70.4 (15.2)
62.4 (8.6) 65.6 (11.8)
69.7 (11.8) 69.8(11.7)
66 2 (9.5) 64.5 (7.9)
1.08 (1.01) 0.96 (0.89)
3.09(1.03)" 0.70 (0.69)
1.95 (0.95) 2.05 (0.78)
4 23 (1 32)'' 1 85 (0.70)
' Values represent means and SDs. '' p < 0.001, pre-post difference compared to placebo (I test). p < 0.05, pre-post difference compared to placebo (t test). d p < 0.01, pre-post difference compared to placebo (t test). c
340
Psychosomatic Medicine 52:337-345 (1990)
BLOOD PRESSURE RESPONSE TO COFFEE
levels before and after the consumption of caffeine and the placebo are presented in Table 1. In addition, Table 1 indicates values for t tests calculated separately for 8 A.M. and 11 A.M. on placebo versus caffeine pre/post differences. Systolic and diastolic blood pressures are higher after caffeine during both times of day. The t tests comparing subjects given caffeine at 8 and 11 A.M. on days 3 and 4 with those subjects given'caffeine at the same times on days 7 and 8 were not significant. The lower the subject's pre-coffee caffeine serum level, the higher the systolic blood pressure response to caffeine, both in the 8 A.M. session (r = -0.60, p < 0.01) and in the 11 A.M. session (r = —0.62, p < 0.01), as shown in Figure 2. Comparable
1 Fig 2
2
3
4
SERUM CAFFEINE
INTRODUCTION
Because of the widespread use of caffeine in the general population (1), there is considerable concern about its possible role in heart disease and hypertension (see review by Ernster (2)). If one looks at the acute effects of caffeine on blood pressure, there is general agreement that both systolic and diastolic blood pressure can be increased substantially for at least a few hours. The caffeine equivalent of two to three cups of coffee was reported to increase the pressor response in healthy, non-coffee-drinking adults (3-5) and in healthy coffee or tea drinkers who had abstained from caffeine for 9-24 hours (6-
From the Department of Psychiatry and Biobehavioral Sciences. University of California, Los Angeles (1 B.G.. D.S.), and the Division of Clinical Pharmacology. University of California School of Medicine, Los Angeles (K.K.H., J.L.Y.). Address reprint requests to: Iris B. Goldstein. Ph.D., Department of Psychiatry. UCLA, 760 Westwood Plaza, Los Angeles. CA 90024-1759. Received August 21, 1989; revision received November 27, 1989.
Psychosomatic Medicine 52:337-345 (1990) OO33-3174/9O/S2O2-O337SO2 00/0 Copyright © 1990 by the American Psycho
8). While there is little question that caffeine can elevate blood pressure acutely, some studies indicate that tolerance develops with habitual caffeine use, resulting in the cessation of pressor responses to caffeine ingestion. The clearest evidence comes from a study by Robertson et al. (9), who showed that after the third day of consuming 250 mg of caffeine, three times a day, there were no longterm effects of caffeine on blood pressure. Although there was no control of coffee intake, Ammon et al. (10) also showed that regular ingestion of coffee (504 mg per day) no longer affected blood pressure after day 5. The acute effects of caffeine on blood pressure are related to the pattern of caffeine use and the amount of caffeine regularly consumed. Many studies indicate that typical coffee and tea drinkers show a pressor response after overnight abstinence (9-12 hours) (6-8, 11-13). These pressor effects are also dependent on basal plasma caffeine concentration. Individuals who exhibited a short caffeine plasma half-life had low plasma caffeine levels after normal overnight abstinence from caffeine. As a result, the morning 337
GOLDSTEIN et al. cup of coffee elicited a pressor response despite the phenomenon of adaptation (14). The purpose of the present investigation was to look at the effects of repeated caffeine intake on blood pressure in a group of healthy, normotensive young male coffee-drinkers who were given prescribed amounts of caffeine to be taken daily throughout the study. Subjects were asked to take 150 mg of caffeine (the equivalent of two cups of instant or one cup of drip coffee) (15), three times a day, a dose level and pattern of usage simulating normal coffee-drinking. The study focuses on the initial morning blood pressure reaction to caffeine after 12 hours of abstinence, as well as the mid-morning response to the second cup of coffee a few hours later. In addition, serum caffeine levels were obtained to determine the relationship between the caffeine concentration in the blood and the pressor response. The study employed a randomized double-blind crossover design.
Procedures
Subjects were asked to consume standardized amounts of caffeine during the period of the study (8 days). They were supplied with prepackaged individual servings of decaffeinated coffee and 150-mg capsules of caffeine, and instructed to combine the contents of a caffeine capsule and the coffee packet in a cup of hot water. In trying to approximate normal coffee-drinking habits, we told the subjects to drink the coffee with breakfast. 1 hour before lunch, and with dinner. If dinner was going to be later than 6 P.M., subjects were to drink their last cup of coffee between 5 and 6 P.M. No other sources of caffeine were to be consumed. In order to increase compliance, subjects were told that blood samples would be drawn during each laboratory session in order to determine the amount of caffeine that had been consumed. During the week that the subject was maintaining his coffee schedule of three cups per day, he came into the laboratory on four different sessions. On these occasions the coffee was consumed in the laboratory rather than at home or at work. After the subject had been drinking coffee for 2 days, on the third day he had a cup of coffee with a light breakfast and reported to the laboratory for Session I at 1 hour before his usual lunch time (about 11 A.M.). The subject returned to the laboratory the following morning at 8 A.M. (Session 2). after not having smoked or consumed anything except water during the preceding 12 hours. Three days later he came back to the laboratory before lunch (Session 3) and again on the following morning (Session 4), as in the prior two sessions (Fig. 1). The laboratory sessions METHODS were held on four separate days, so that each session would be uncontaminated by any other laboratory session. In this way subjects could be studied on as typical a coffee-drinking schedule as possible. Subjects The subject was given coffee in the laboratory during all four occasions in a randomized doubleTwenty healthy white males between the ages of blind procedure. Sessions were each counterbal18 and 35 years (mean = 25) participated in the anced so that every subject received 150 mg of study. They signed a consent form approved by the caffeine in one morning session and a placebo in the UCLA Human Subject Protection Committee. Partic- other, combined with decaffeinated coffee. The ipation was confined to individuals who were regu- same counterbalancing occurred for mid-morning lar coffee drinkers. Caffeine content of each subject's sessions. To make certain that a subject always rediet was determined from individual self-reports ceived 150 mg of caffeine three times a day, he was (15). Daily caffeine intake of subjects ranged from 84 always given a second cup of coffee before leaving to 830 mg (mean = 338.8 mg). Anyone taking medi- the laboratory. If the subject received caffeine durcations or involved in any kind of medical treatment ing the test session, he was given coffee with a was excluded. Most of the men were non-smokers, placebo at the end of the session. If, on the other except for four subjects who smoked occasionally hand, this was a placebo session, he would be given (less than one pack per month). caffeinated coffee before he left. Subsequent ques338
Psychosomatic Medicine 52:337-345 (1990)
BLOOD PRESSURE RESPONSE TO COFFEE
DAY
1
2
3
4
5
6
7
LAB
8:00 AM
CAFFEINE
CAFFEINE
CAFFEINE
CAFFEINE
CAFFEINE
LAB
11:00 AM
CAFFEINE
CAFFEINE
5:00 PM
CAFFEINE
CAFFEINE
CAFFEINE
'IRCEBO
LAB CAFFEINE
CAFFEINE
8 LAB
CAFFEINE
CAFFEINE
CAFFENE CAFFEINE CAFFEINE
CAFFEINE
CAFFENE
CAFFEINE
Fig. 1. The schedule of caffeine consumption during the study, whereby subjects drank 150 mg of caffeine at home three times a day. Exceptions to this were laboratory sessions on days 3 and 7 at 11 A.M. and days 4 and 8 at 8 A.M. On these days subjects received either caffeine or placebo in the laboratory, counterbalanced.
tioning revealed that subjects were unable to discriminate between the caffeine and the placebo sessions. Except for the administration of either caffeine or placebo, all of the sessions were the same. After the subject sat quietly for 10 minutes, six blood pressure measurements were obtained with a Baumanometer mercury column sphygmomanometer, with a 1-minute delay between each measurement, according to the guidelines of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (16). Two radial pulse determinations (30 seconds each) were also taken. The average of the last five blood pressure readings and the two pulse readings were used in later analyses. All blood pressure and heart rate measurements were made by one of the authors (I. B. G.). Blood was drawn from the antecubital vein to determine serum concentrations of caffeine, which were analyzed with a reverse phase high performance liquid chromatography method (17). The subject was given 5 minutes to drink a cup of coffee. On the first 2 days he completed each of two halves of a detailed questionnaire on caffeine intake (18). The subject then sat quietly reading magazines. Because peak plasma levels for caffeine are generally reached within 15 to 45 minutes after ingestion (19) and peak blood pressure is reached at 60 minutes (3), we waited 45 minutes before taking final blood pressures. At that
Psychosomatic Medicine 52:337-345 (1990)
time two additional pulse and six blood pressure measurements were recorded, followed by a second blood draw. The subject drank a second cup of coffee (placebo or caffeine) and left the laboratory.
Statistical Analyses A repeated measures two-way within-subject analysis of variance (ANOVA) was computed on precoffee levels of systolic blood pressure, diastolic blood pressure, heart rate, and serum caffeine for time of day (8 A.M., 11 A.M.) x coffee condition (caffeine, placebo), and a similar ANOVA on the difference between pre- and post-coffee values was performed for each of the above variables. In order to determine whether the effects of caffeine were consistent over time, subjects given caffeine at 11 A.M. on day 3 were compared with subjects given caffeine at 11 A.M. on day 7. This was done by dividing subjects into two groups in a betweensubject ( test of post- minus pre-caffeine measures of heart rate, systolic blood pressure, diastolic blood pressure, and serum caffeine levels. Similar ( tests were run comparing the effects of 8 A.M. doses of caffeine given on day 4 as compared with day 8. Pearson r correlations were computed to determine the relationship between caffeine usage, blood pressure values, and serum caffeine levels.
339
GOLDSTEIN et al.
RESULTS
Placebo-Caffeine Differences The placebo-caffeine difference was Pre-Coffee Values significant for systolic blood pressure Pre-/Post-Coffee values (placebo or caf- [F(l/19) = 18.0, p < 0.0001] and for diafeine) for all measures are shown in Table stolic blood pressure [F(l/19) = 31.9, p < 1. There were no significant differences 0.0001], but not for heart rate. The caffeine in subjects' blood pressure or heart rate blood pressure change relative to the plaprior to drinking coffee for time of day or cebo was 5.8/6.5 mm Hg in the early coffee condition (placebo versus caffeine). morning (8 A.M.) and 2.4/5.2 mm Hg at Pre-coffee serum caffeine levels were sig- mid-morning (11 A.M.). A somewhat nificantly higher at the 11 A.M. session lesser effect for systolic blood pressure than at the 8 A.M. session [F(l/19) = 38.1, during mid-morning was indicated by a p < 0.0001]. The mean pre-coffee levels, placebo-caffeine interaction that was staaveraged for the caffeine and placebo con- tistically close to significance (p = 0.052). ditions, were 1.02 fig/ml at 8 A.M. and 2.0 Serum caffeine levels were significantly /ug/ml at 11 A.M. Although the level of higher after ingesting the caffeine as compre-coffee serum caffeine was higher at pared to the placebo [F(l/19) = 225.8, p < 11 A.M. than at 8 A.M., there were no 0.0001]. Relative to the placebo, serum associated differences in the pre-coffee caffeine levels increased in the caffeine blood pressure or heart rate. In spite of condition by 2.21 jug/ml in the 8 A.M. the blood pressure elevating effect of caf- session and 2.48 jug/ml in the 11 A.M. feine that had occurred early in the morn- session. There was no time of day effect. ing, this effect was not seen at the 11 A.M. Systolic blood pressure, diastolic blood session. pressure, heart rate, and serum caffeine TABLE 1.
Pre- and Post-Coffee Systolic and Diastolic Blood Pressure, Heart Rate, and Serum Caffeine Levels" 11 A M .
8 A.M. Pre Systolic BP (mm Hg) Caffeine Placebo Diastolic BP (mm Hg) Caffeine Placebo Heart Rate (bpm) Caffeine Placebo Scrum Caffeine (Mg/ml) Caffeine Placebo
Post
Pre
Post
115 1 (7.9) 117.0(7.8)
118.2 (9.4)'1 114 3(9.7)
116.4 (6.8) 116.6 (9.0)
116.2 (8 7)c 114.0(8.6)
74.2 (6.0) 75.7(6.3)
79.7 (4.7)fc 74.7 (5.6)
74.0 (8.3) 75.6 (6.4)
78.7 (7.0)" 75 1 (7 3)
66.6 (11.4) 70.4 (15.2)
62.4 (8.6) 65.6 (11.8)
69.7 (11.8) 69.8(11.7)
66 2 (9.5) 64.5 (7.9)
1.08 (1.01) 0.96 (0.89)
3.09(1.03)" 0.70 (0.69)
1.95 (0.95) 2.05 (0.78)
4 23 (1 32)'' 1 85 (0.70)
' Values represent means and SDs. '' p < 0.001, pre-post difference compared to placebo (I test). p < 0.05, pre-post difference compared to placebo (t test). d p < 0.01, pre-post difference compared to placebo (t test). c
340
Psychosomatic Medicine 52:337-345 (1990)
BLOOD PRESSURE RESPONSE TO COFFEE
levels before and after the consumption of caffeine and the placebo are presented in Table 1. In addition, Table 1 indicates values for t tests calculated separately for 8 A.M. and 11 A.M. on placebo versus caffeine pre/post differences. Systolic and diastolic blood pressures are higher after caffeine during both times of day. The t tests comparing subjects given caffeine at 8 and 11 A.M. on days 3 and 4 with those subjects given'caffeine at the same times on days 7 and 8 were not significant. The lower the subject's pre-coffee caffeine serum level, the higher the systolic blood pressure response to caffeine, both in the 8 A.M. session (r = -0.60, p < 0.01) and in the 11 A.M. session (r = —0.62, p < 0.01), as shown in Figure 2. Comparable
1 Fig 2
2
3
4
SERUM CAFFEINE
