Caffeine effects on cardiovascular and neuroendocrine responses to acute psychosocial stress and their relationship to level of habitual caffeine consumption

The effects of a moderate dose of caffeine on cardiovascular and neuroendocrine stress reactivity were examined in 25 healthy male subjects selected as habitual or light consumers of caffeine. Measurements were taken under resting conditions before and after administration of caffeine (3.5 mg/kg) or placebo, during a stressful laboratory task, and in a post-stress recovery period. Caffeine elevated blood pressure and plasma norepinephrine levels at rest, effects which added significantly to the effects of stress. Caffeine potentiated stress-related increases in plasma epinephrine and cortisol stress, more than doubling the responses observed in the control condition. These effects were present in both habitual and light consumers and level of habitual caffeine consumption did not affect their magnitude. Results indicate that caffeine can potentiate both cardiovascular and neuroendocrine stress reactivity and that the habitual use of caffeine is not necessarily associated with the development of tolerance to these effects.     

Effects of caffeine on plasma renin activity, catecholamines and blood pressure.

Using a double-blind, randomized, cross-over protocol, we studied the effect of a single dose of oral caffeine on plasma renin activity, catecholamines and cardiovascular control in nine healthy, young, non-coffee drinkers maintained in sodium balance throughout the study period. Caffeine (250 mg) or placebo was administered in a methylxanthine-free beverage to overnight-fasted supine subjects who had had no coffee, tea or cola in the previous three weeks. Caffeine increased plasma renin activity by 57 per cent, plasma norepinephrine by 75 per cent and plasma epinephrine by 207 per cent. Urinary normetanephrine and metanephrine were increased 52 per cent and 100 per cent respectively. Mean blood pressure rose 14/10 mm Hg one hour after caffeine ingestion. There was a slight fall and then a rise in heart rate. Plasma caffeine levels were usually maximal one hour after ingestion but there was considerable individual variation. A 20 per cent increase in respiratory rate correlated well with plasma caffeine levels. Under the conditions of study caffeine was a potent stimulator of plasma renin activity and adrenomedullary secretion. Whether habitual ingestion has similar effects remains to be determined.     

Cardiovascular Effects of Caffeine and Stress in Regular Coffee Drinkers

The effects of caffeine on cardiovascular activity at rest and in response to psychological stress were studied in a group of 30 healthy males who were regular coffee drinkers to replicate caffeine-stress interactions found previously in caffeine-naive subjects. Measures of heart rate, blood pressure, and forearm blood flow were recorded at rest and during the performance of a stressful mental task in two separate sessions. Caffeine (250 mg) or placebo was administered double-blind in a within-subject design. Relative to placebo, caffeine had a pressor effect at rest which persisted during stress and recovery such that blood pressure during stress was higher if caffeine had been consumed. Caffeine also magnified the forearm blood flow and forearm vascular resistance responses to stress, suggestive of a synergistic interaction of caffeine and stress. Analysis of individual difference variables suggested that caffeine effects on the forearm vascular variables were greatest in subjects who were Type B and had a positive family history of hypertension. Results suggest that regular caffeine use does not necessarily lead to tolerance for caffeine-stress interactions and that certain characteristics may be associated with greater sensitivity to caffeine's effects.     

The effects of caffeine on ambulatory blood pressure,heart rate,and mood in coffee drinkers

The present study examined the effects of caffeine, as typically ingested through coffee, on ambulatory systolic and diastolic blood pressure (BP), heart rate, and mood. Normotensive coffee drinkers wore a BP monitor for two 24-hr periods, consuming decaffeinated coffee. Each cup was supplemented with 125 mg caffeine or cornstarch. Systolic and diastolic BPs were elevated on the day caffeine was consumed (maximum, 3.6 and 5.6 mm Hg, respectively), most notably shortly after ingestion. Heart rate was higher overnight following caffeine consumption. Negative Affectivity was also increased by caffeine, but Positive Affectivity and tiredness were unaffected.     

Caffeine Affects Cardiovascular Responses to Stress

The effects of caffeine on cardiovascular activity at rest and during psychological stress were examined in 33 healthy male college students who did not normally ingest caffeinated products. Caffeine (250 mg) and placebo were administered double-blind in separate sessions. Heart rate, blood pressure, and forearm blood flow and vascular resistance were assessed at rest and during the stressful, competitive performance of a mental arithmetic task. Comparisons of caffeine and placebo sessions revealed that caffeine elevated resting blood pressure 4–6 mmHg, an effect which added to the elevation produced by stress. Caffeine did not affect resting forearm blood flow but potentiated the forearm blood flow response to stress and led to higher levels of flow during stress. No caffeine effects appeared in heart rate or in task performance. Family history of hypertension and Type A behavior were examined as potential modulating factors of caffeine effects but results were generally negative. These results suggest possible mechanisms through which caffeine could enhance the pathogenic effects of stress on the cardiovascular system.     

Caffeine, mental stress, and risk for hypertension: a cross-cultural replication

Separate and combined effects of caffeine and mental arithmetic stress on systolic blood pressure (SBP) and heart rate (HR) were assessed in a double-blind, placebo-controlled study. Thirty-six Chinese nationals, half with and half without a family history of hypertension, received either 0, 125, or 250 mg of caffeine in three separate experimental sessions, each preceded by a 12-hour abstention from caffeine consumption. Caffeine and mental stress elevated SBP, but caffeine did not potentiate the SBP response to mental stress. Caffeine did not affect HR. A positive family history of hypertension was associated with larger SBP elevations to the higher dose of caffeine. Family history of hypertension was associated with larger blood pressure elevations during mental stress, but only under conditions of high-level stimulation provided by the initial exposure to the stress. These results support previous findings of greater cardiovascular reactivity to laboratory stress in individuals at high risk for hypertension.     

Hemodynamic and humoral effects of caffeine in autonomic failure. Therapeutic implications for postprandial hypotension

We examined the effects of caffeine and meals on blood pressure and heart rate in 12 patients with autonomic failure. The influence of caffeine on plasma norepinephrine, epinephrine, and renin activity was also studied. Caffeine 250 mg, raised blood pressure by 12/6 mm Hg, from 129 +/- 25/78 +/- 12 (mean +/- S.D.) to a maximum of 141 +/- 30/84 +/- 16 mm Hg at 45 minutes (P less than 0.01), but did not change heart rate, levels of norepinephrine, or epinephrine, or plasma renin activity. Blood pressure fell by 28/18 mm Hg after a standardized meal, from 133 +/- 32/80 +/- 15 to a minimum of 105 +/- 21/62 +/- 12 mm Hg at 60 minutes (P less than 0.01). After pretreatment with 250 mg of caffeine, the standardized meal induced a fall of only 11/10 mm Hg, from 140 +/- 33/79 +/- 7 to 129 +/- 31/69 +/- 13 mm Hg at 60 minutes (P less than 0.05 vs. values after the control per day for seven days) in five patients, postprandial blood pressures remained higher after caffeine than after placebo (P less than 0.05). We conclude that caffeine is a pressor agent and attenuates postprandial hypotension in autonomic failure, and that this effect is not primarily due to elevations in sympathoadrenal activity or activation of the renin-angiotensin system. Caffeine may be useful in the treatment of orthostatic hypotension due to autonomic failure, especially in the postprandial state.     

The influence of user status and anxious disposition on the hypertensive effects of caffeine

The present study examined the influence of consumer status and anxious disposition on the hypertensive effects of caffeine. A secondary aim of the study was to investigate possible gender differences in response to caffeine. Sixty normotensive subjects were assigned to 4 groups representing high and low scorers on the variables of habitual caffeine consumption and anxious disposition. A randomized double-blind crossover design was used in which all subjects received a placebo (lactose) at one of two 120-min laboratory sessions and caffeine (6 mg/kg) at the other. Systolic and diastolic blood pressure, heart rate, hand steadiness, and EMG were monitored before and after exposure to a psychological stressor. Caffeine produced significant elevations in systolic and diastolic blood pressure, and these effects were additive to the pressor effects of stress and anxiety. While the general pattern of results was similar for both sexes, reactions to caffeine were more pronounced in males than in females. Notwithstanding the need for clarification of the chronic effects of caffeine, present findings add further weight to current concerns about the acute hypertensive effects of the drug.     

Videotape preparation of patients before hip replacement surgery reduces stress

OBJECTIVE: Elective surgery represents a considerable source of stress for the patient. Many attempts have been made to prepare patients before surgery with the aim of reducing stress and improving outcome. This study used a novel approach to fulfill this aim by showing a videotape of a patient undergoing total hip replacement surgery, covering the time period from hospital admission to discharge, that strictly keeps to the patient's perspective. METHODS: Before elective total hip replacement surgery, 100 patients were randomly assigned to a control group or a preparation group; the latter group was shown the videotape on the evening before surgery. Anxiety and pain were evaluated daily for 5 days, beginning with the preoperative day, by means of the State-Trait Anxiety Inventory and a visual analog scale. Intraoperative heart rate and blood pressure, as well as postoperative intake of analgesics and sedatives, were recorded. Urinary levels of cortisol, epinephrine, and norepinephrine were determined in 12-hour samples collected at night for 5 nights, beginning with the preoperative night. RESULTS: Compared with the control group, the preparation group showed significantly less anxiety on the morning before surgery and the mornings of the first 2 postoperative days, and significantly fewer of them had an intraoperative systolic blood pressure increase of more than 15%. The pain ratings did not differ significantly between the two groups, but the prepared patients needed less analgesic medication after surgery. Prepared patients had significantly lower cortisol excretion during the preoperative night and the first 2 postoperative nights. Excretion of catecholamines did not differ significantly between groups. CONCLUSIONS: We conclude that use of the videotape decreased anxiety and stress, measured in terms of urinary cortisol excretion and intraoperative systolic blood pressure increase, in patients undergoing hip replacement surgery and prepared them to cope better with postoperative pain.     

Caffeine, extended stress, and blood pressure in borderline hypertensive men

Caffeine increases blood pressure (BP), and its pressor effects are larger in borderline hypertensive (BH) men than in controls. This article extends findings of larger caffeine effects on BP at rest and to brief mental stress in BH to a new analysis of caffeine and prolonged mental stress in BH. In a double-blind, crossover study, 24 male BH (140/90 mmHg < BP < 160/95 mmHg) and 23 normotensive controls who were habitual caffeine consumers (NT; BP < 135/85 mmHg; negative parental history) worked on alternating mental stressors for 35 min after placebo or caffeine (3.3 mg/kg). Caffeine raised systolic blood pressure (SBP) and diastolic blood pressure (DBP) alone and during the extended tasks (all ps < .00001/.00001). BH had larger SBP and DBP increases over all postcaffeine periods (ps < .04/04) and larger DBP rises to the extended tasks after caffeine (p = .007). These combined effects led to undesirably high BPs (> 140/82 mmHg) relative to controls (< 130/75) during the 100 min after caffeine intake. Caffeine taken by BH at times of extended behavioral stress may elevate BP to a clinically meaningful degree. This research was supported by the Medical Research Service of the Department of Veterans Affairs and the National Heart Lung and Blood Institute of the National Institutes of Health, grant numbers HL32050 and HL07640. We thank Barbara McKey and Judith Silverstein for their efforts in data collection and Terrie Thomas for her valuable comments on an earlier version of this article.     

Cerebral blood flow and behavioural effects of caffeine in habitual and non-habitual consumers of caffeine: a near infrared spectroscopy study

Caffeine has been shown to modulate cerebral blood flow, with little evidence of tolerance to these effects following habitual use. However, previous studies have focused on caffeine levels much higher than those found in dietary servings and have compared high caffeine consumers with low consumers rather than ‘non-consumers’. The current placebo-controlled double-blind, balanced-crossover study employed near infrared spectroscopy to monitor pre-frontal cerebral-haemodynamics at rest and during completion of tasks that activate the pre-frontal cortex. Twenty healthy young habitual and non-habitual consumers of caffeine received 75 mg caffeine or placebo. Caffeine significantly decreased cerebral blood flow but this was subject to a significant interaction with consumption status, with no significant effect being shown in habitual consumers and an exaggerated effect in non-habitual consumers. These findings suggest that caffeine, at levels typically found in a single dietary serving, is able to modulate cerebral blood flow but these effects are subject to tolerance.     

Adrenocortical effects of caffeine at rest and during mental stress in borderline hypertensive men

We examined the effect or dietary doses of caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee) on adrenocortical responses to behavioral stress in borderline hypertensive (BH) men using a randomized, double-blind, caffeine-placebo crossover design. Cortisol levels were assessed in BH men and matched normotensive (NT) controls at rest and in response to 35 min of continuous work on a psychomotor task alternating with mental arithmetic. Caffeine at rest elevated cortisol among BHs hut not among NTs. Both groups showed significant cortisol responses to caffeine combined with the tasks. These findings may have implications for the dietary use of caffeine in persons at risk for hypertension when faced with stressful situations.     

Social support at work, heart rate, and cortisol: a self-monitoring study

This study assessed the influence of work social support on self-monitored heart rate, blood pressure, and salivary cortisol recorded on 3 work days and 2 leisure days from 61 nurses and 32 accountants (40 men, 53 women). Heart rate and blood pressure were higher during the day at work than in the evening or on leisure days. Cortisol was higher on leisure than work days and was lower in the evening than in the day. Low social support at work was associated with elevated heart rate during the daytime and evening of work days, an effect that persisted after controlling for psychological distress, age, sex, smoking, and physical activity. Work social support was not related to cortisol on work days, but on leisure days cortisol was elevated among individuals reporting high social support. There were few differences between men and women, and no important occupational effects.     

The impairment of gastroduodenal mucosal barrier by coffee

BACKGROUND: Even though coffee is not considered to be responsible for development of peptic ulcer, it may, however, prolong its healing by increasing acidity of gastric content. In our former work we observed a profound increase in sucrose permeability (above normal values) in healthy volunteers regularly drinking coffee for years. In literature, many factors affecting sucrose permeability have been described so far. None of them, however, studied the effect of coffee. Subjects, materials and methods: 10 young asymptomatic habitual coffee drinkers were included in the study. The probands underwent SaLM test twice--first time without coffee restriction and second time after 48-hour coffee abstinence. The ingested SaLM solution comprised sucrose (25.0 g), lactulose (10.0 g), mannitol (2.0 g), xylose (2.0 g) and water (up to 100 ml). Urine was collected for five hours and the samples were analysed using gas chromatography. Results were compared with those of 8 young healthy volunteers not drinking coffee. Permeability for sucrose was significantly higher in the group of habitual coffee drinkers in comparison with non-coffee drinkers (p < 0.01). After 48-hour coffee abstinence sucrose excretion decreased significantly (p < 0.05) to a level not differing from that of non-coffee drinkers (p = 0.54). CONCLUSIONS: Our results indicate that coffee may damage gastroduodenal mucosa in habitual coffee drinkers. In a time period of 48 hours the gastroduodenal mucosa is capable of a significant regeneration.     

Serum lipids, neuroendocrine and cardiovascular responses to stress in healthy Type A men.

This study examined the relationship between serum lipid activity in healthy Type A men and cardiovascular and neuroendocrine responses to a behavioral stressor, mental arithmetic. Assessment of blood lipids included measures of total cholesterol (TC), low density lipoprotein cholesterol (LDLC), high density lipoprotein cholesterol (HDLC), and serum triglycerides. Cardiovascular (blood pressure and heart rate) and neuroendocrine (epinephrine, norepinephrine and cortisol) responses were recorded before (rest), during (stress) and after (recovery) the mental arithmetic test. Diastolic blood pressure, mean arterial pressure and, to a lesser extent, systolic blood pressure levels at rest, during stress, and at recovery correlated positively with TC levels. In addition, both diastolic and mean arterial pressure were positively correlated with the ratio of TC to HDLC and with triglycerides during stress and recovery. Heart rate did not correlate with any lipid measure. Cardiovascular stress-reactivity calculated as change from rest to stress did not correlate significantly with any lipid measure. Plasma norepinephrine during stress correlated positively with triglycerides; a similar trend was observed for the TC/HDLC ratio. Plasma cortisol at rest and during stress correlated positively with the TC/HDLC ratio and serum triglycerides, and negatively with HDLC. Plasma norepinephrine reactivity calculated as change from rest to stress correlated negatively with HDLC and positively with triglycerides. In addition, cortisol reactivity was positively correlated with triglycerides. It is suggested that the mechanisms mediating Type A behavior and coronary heart disease may include increased cardiovascular and neuroendocrine responses as well as unfavorable lipid profiles.     

The effect of caffeine abstinence on sleep among habitual caffeine users with poor sleep

Caffeine is the most widely used psychoactive substance in the world and is known to disrupt healthy sleep. However, very few studies have directly tested the effect of caffeine abstinence on sleep, and these have yielded inconsistent findings. The purpose of the present study was to examine changes in sleep following caffeine abstinence and examine the extent to which characteristics of habitual caffeine use moderated this change. Participants included 66 healthy, young adults with habitual caffeine use and poor sleep. During the 2‐week baseline, sleep was assessed using wrist actigraphy and daily caffeine use was assessed with bedtime diaries. Eligible participants then completed 1 week of caffeine abstinence, during which sleep was measured with wrist actigraphy. Multilevel models found no significant differences between either mean levels or growth trajectories of total sleep time or sleep efficiency between baseline and caffeine abstinence. Mean levels of sleep onset latency also did not differ between baseline and caffeine abstinence. A small but significant quadratic effect was observed, such that sleep onset latency decreased during the first few days of caffeine abstinence, then increased to levels above baseline. Characteristics of caffeine use did not moderate changes in sleep between baseline and caffeine abstinence. These data suggest that abstaining from caffeine may not result in long‐term sleep improvement for habitual caffeine users, which contradicts the common sleep health recommendation. The present findings encourage more rigorous investigation of the effectiveness of caffeine restriction on sleep.     

Ambulatory cardiovascular activity in Vietnam combat veterans with and without posttraumatic stress disorder

The present study investigated the relationship between daily diary affect ratings and ambulatory cardiovascular activity in 117 male Vietnam combat veterans (61 with posttraumatic stress disorder [PTSD] and 56 without PTSD). Participants completed 12-14 hr of ambulatory monitoring and daily diary affect ratings. Compared with veterans without PTSD, veterans with PTSD reported higher negative affect and lower positive affect in daily diary ratings. No differences were detected for mean laboratory initial recordings or mean ambulatory heart rate (HR), systolic blood pressure (SBP), or diastolic blood pressure (DBP). However, compared with veterans without PTSD, veterans with PTSD demonstrated higher SBP and DBP variability and a higher proportion of HR activity (compared with initial recording values) during daily activity. There was a significant Time of Day x Group interaction for mean HR, with a trend for PTSD participants to maintain HR levels during evening hours.     

Gastric acid secretion and lower-esophageal-sphincter pressure in response to coffee and caffeine.

Caffeine stimulates gastric acid secretion and reduces the competence of the lower esophageal sphincter in man. These effects of caffeine have been used as evidence that regular coffee should not be used by patients with peptic-ulcer disease or gastroesophageal reflux. We compared the dose-response relations of caffeine, regular coffee and decaffeinated coffee for gastric acid secretion and sphincter pressure in normal subjects. Decaffeinated coffee gave a maximal acid response of 16.5 +/- 2.6 mEq per hour (mean +/- S.E.M.), which was similar to that of regular coffee, 20.9 +/- 3.6 mEq per hour, both values being higher than that of caffeine, 8.4 +/- 1.3, on a cup-equivalent basis. Sphincter pressure showed minimal changes in response to caffeine, but was significantly increased by both regular and decaffeinated coffee (P less than 0.05). These data suggest that clinical recommendations based upon the known gastrointestinal effects of caffeine may bear little relation to the actual observed actions of coffee or decaffeinated coffee.     

Positive affect is associated with cardiovascular reactivity, norepinephrine level, and morning rise in salivary cortisol

Positive affect was examined as a predictor of (1) cardiovascular reactivity during a sadness and an anger recall task and recovery following the protocol, (2) epinephrine (EPI) and norepinephrine (NOREPI) reactivity and level during the recall protocol, and (3) the diurnal pattern of salivary cortisol. Sample was 328 individuals. Negative affect, age, race, sex, smoking status, income, and BMI were adjusted. During sadness recall, positive affect was inversely related to systolic blood pressure ( p =.007) and diastolic blood pressure ( p =.049) reactivity, and unrelated to heart rate ( p =.226). Positive affect was unrelated to reactivity during anger recall ( p s>.19), and was unrelated to recovery at the end of the recall protocol. Positive affect was inversely related to the mean level of NOREPI ( p =.046), and unrelated to EPI ( p =.149). Positive affect was inversely related to the increase in cortisol 30 min post awakening ( p =.042), and unrelated to the evening decline in cortisol levels ( p =.174). Positive emotions may be relevant to good health.