Caffeine and hypertension

The effects of caffeine supplementation on blood pressure in adults: A systematic review and dose-response meta-analysis

BACKGROUND AND AIMS

Hypertension is a serious complication linked to a higher risk for organs. Caffeine is a natural component that affects the cardiovascular system, while the mechanisms of its effects are not fully established. Therefore, we aimed to examine the impact of caffeine supplementation on blood pressure (BP) by conducting a systematic review and dose-response meta-analysis of randomized controlled clinical trials (RCTs).

METHODS AND RESULTS

We searched online databases using relevant keywords up to July 2022 to identify RCTs using caffeine on systolic (SBP) and diastolic BP (DBP) in adults. Inclusion criteria were adult participants ≥18 years old for subjects, examining the effect of caffeine supplementation on BP, and RCTs studies. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence (CI). The pooled of 11 effect sizes analysis of 8 studies demonstrated significant increases in SBP (WMD:1.94 mmHg; 95%CI:0.52, 3.35; p = 0.007) and DBP (WMD:1.66 mmHg; 95% CI:0.75, 2.57; p = 0.000) after caffeine supplementation. The subgroup analysis showed that caffeine supplementation more effectively increased SBP and DBP in males than females. Moreover, meta-regression analysis demonstrated a significant relationship between the dose of caffeine intake and changes in SBP (p = 0.000), DBP (p = 0.000), and duration of the trial in SBP (p = 0.005), and DBP (p = 0.001). The non-linear dose-response analysis detected the dosage of supplementation >400 mg/day is effective for increasing DBP (p = 0.034), and the duration of supplementation of more than nine weeks makes increasing in both SBP and DBP.

CONCLUSION

This meta-analysis shows that caffeine supplementation significantly increased SBP and DBP in adults.

Systematic and regional haemodynamic effects of caffeine and alcohol in fasting subjects

It is well established that caffeine and alcohol can have acute effects on heart rate and blood pressure, but it is not known whether cardiac output and peripheral blood flow are also affected. Such information is needed before any possible effects of caffeine or alcohol on the haemodynamic responses to food can be assessed. Thus, the present study determined the haemodynamic effects of caffeine or alcohol. Eight healthy young subjects were studied in the fasting state before and after ingestion of water (200 ml), coffee containing caffeine (3.5 mg/kg in 200 ml) or alcohol (0.5 g/kg made up to 200 ml) , in random order on three separate occasions. All of the subjects had abstained from both caffeine and alcohol for at least 12 h. Measurements of blood pressure (BP), heart rate (HR), cardiac output (CO), superior mesenteric artery blood flow (SMABF) and calf blood flow (CBF) were made at baseline and for 2 h after each drink. With the alcohol drink, blood alcohol levels estimated using breath measurement peaked at 18.8 mmol/l. HR fell slightly after water but increased after alcohol (+ 7 beats/min) and after caffeine (+ 16 beats/min, group × time interaction analysis of variance, p < 0.03), with peak responses at 40-60 min and a return to baseline by 120 min. Systolic BP increased significantly with time after all three drinks , with no significant differences between the drinks. CBF rose slightly after the drink of water, more so after alcohol but fell slightly after caffeine (group × time interaction analysis of variance, p < 0.01). Total peripheral resistance rose slightly after water and alcohol but much more markedly after caffeine (group effect analysis of variance, p < 0.001). There were no significant effects of alcohol or caffeine on the other variables. Thus, caffeine and alcohol themselves have haemodynamic effects which might interact with the effects of food.

Towards an expert consensus to delineate a clinical syndrome of chronic breathlessness

Breathlessness that persists despite treatment for the underlying conditions is debilitating. Identifying this discrete entity as a clinical syndrome should raise awareness amongst patients, clinicians, service providers, researchers and research funders.Using the Delphi method, questions and statements were generated via expert group consultations and one-to-one interviews (n=17). These were subsequently circulated in three survey rounds (n=34, n=25, n=31) to an extended international group from various settings (clinical and laboratory; hospital, hospice and community) and working within the basic sciences and clinical specialties. The a priori target agreement for each question was 70%. Findings were discussed at a multinational workshop.The agreed term, chronic breathlessness syndrome, was defined as breathlessness that persists despite optimal treatment of the underlying pathophysiology and that results in disability. A stated duration was not needed for "chronic". Key terms for French and German translation were also discussed and the need for further consensus recognised, especially with regard to cultural and linguistic interpretation.We propose criteria for chronic breathlessness syndrome. Recognition is an important first step to address the therapeutic nihilism that has pervaded this neglected symptom and could empower patients and caregivers, improve clinical care, focus research, and encourage wider uptake of available and emerging evidence-based interventions.

Caffeine: Is it Dangerous to Health?

Caffeine is a drug that is a common ingredient of popular foods, beverages, and over-the-counter as well as prescription medications. While at least 30% of Americans consume a moderate amount (200 mg. a day, about two cups of coffee), many others function with a much higher intake, 600 mg. or more (six or more cups of coffee). Researchers are discovering that caffeine may not be as safe as many people believe, since the substance has widespread effects on many body systems. It has also been linked to a variety of ailments, among them anxiety and hypertension, although information linking caffeine to cancer and birth defects is still speculative. In light of the expanding body of knowledge on the deleterious effects of caffeine, individuals should moderate or eliminate their intake of major caffeine-containing foods, beverages, and drugs. Health promotion programs can assist in this goal by providing education and support.

Non-additive genome-wide association scan reveals a new gene associated with habitual coffee consumption

Coffee is one of the most consumed beverages world-wide and one of the primary sources of caffeine intake. Given its important health and economic impact, the underlying genetics of its consumption has been widely studied. Despite these efforts, much has still to be uncovered. In particular, the use of non-additive genetic models may uncover new information about the genetic variants driving coffee consumption. We have conducted a genome-wide association study in two Italian populations using additive, recessive and dominant models for analysis. This has uncovered a significant association in the PDSS2 gene under the recessive model that has been replicated in an independent cohort from the Netherlands (ERF). The identified gene has been shown to negatively regulate the expression of the caffeine metabolism genes and can thus be linked to coffee consumption. Further bioinformatics analysis of eQTL and histone marks from Roadmap data has evidenced a possible role of the identified SNPs in regulating PDSS2 gene expression through enhancers present in its intron. Our results highlight a novel gene which regulates coffee consumption by regulating the expression of the genes linked to caffeine metabolism. Further studies will be needed to clarify the biological mechanism which links PDSS2 and coffee consumption.

Differing chemical compositions of three teas may explain their different effects on acute blood pressure in spontaneously hypertensive rats

BACKGROUND

Heavy tea consumption is suggested to be unsuitable for hypertensive people. However, the bioactive substances in different varieties of tea leaves are very different. This study compares the effects of three Chinese teas - C. sinensis, C. ptilophylla and C. assamica var. kucha - on blood pressure (BP) and heart rate in spontaneously hypertensive rats (SHRs).

RESULTS

Intragastric administration of C. sinensis extract led to an acute increase in systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate in SHRs. However, C. ptilophylla and C. assamica var. kucha exerted no obvious influences on SBP, DBP or heart rate. Similar to the extract of C. sinensis, intragastric administration of caffeine also led to an acute increase in BP and heart rate in SHRs. In contrast, theobromine and theacrine - purine alkaloids predominantly contained in C. ptilophylla and C. assamica var. kucha, respectively - had no pressor effects. The effect of caffeine on BP was related to the regulation of plasma epinephrine and norepinephrine levels in SHRs.

CONCLUSION

The different effects of C. sinensis, C. ptilophylla and C. assamica var. kucha on BP might be explained, at least partially, by the differences in the varieties and contents of purine alkaloids.

Association analysis of bitter receptor genes in five isolated populations identifies a significant correlation between TAS2R43 variants and coffee liking

Coffee, one of the most popular beverages in the world, contains many different physiologically active compounds with a potential impact on people’s health. Despite the recent attention given to the genetic basis of its consumption, very little has been done in understanding genes influencing coffee preference among different individuals. Given its markedly bitter taste, we decided to verify if bitter receptor genes (TAS2Rs) variants affect coffee liking. In this light, 4066 people from different parts of Europe and Central Asia filled in a field questionnaire on coffee liking. They have been consequently recruited and included in the study. Eighty-eight SNPs covering the 25 TAS2R genes were selected from the available imputed ones and used to run association analysis for coffee liking. A significant association was detected with three SNP: one synonymous and two functional variants (W35S and H212R) on the TAS2R43 gene. Both variants have been shown to greatly reduce in vitro protein activity. Surprisingly the wild type allele, which corresponds to the functional form of the protein, is associated to higher liking of coffee. Since the hTAS2R43 receptor is sensible to caffeine, we verified if the detected variants produced differences in caffeine bitter perception on a subsample of people coming from the FVG cohort. We found a significant association between differences in caffeine perception and the H212R variant but not with the W35S, which suggests that the effect of the TAS2R43 gene on coffee liking is mediated by caffeine and in particular by the H212R variant.

No other significant association was found with other TAS2R genes. In conclusion, the present study opens new perspectives in the understanding of coffee liking. Further studies are needed to clarify the role of the TAS2R43 gene in coffee hedonics and to identify which other genes and pathways are involved in its genetics.

Methylxanthines and the kidney

This chapter describes the effects of the natural methylxanthines caffeine and theophylline on kidney function. Theophylline in particular was used traditionally to increase urine out put until more potent diuretics became available in the middle of the last century. The mildly diuretic actions of both methylxanthines are mainly the result of inhibition of tubular fluid reabsorption along the renal proximal tubule. Based upon the use of specific adenosine receptor antagonists and the observation of a complete loss of diuresis in mice with targeted deletion of the A1AR gene, transport inhibition by methylxanthines is mediated mainly by antagonism of adenosine A1 receptors (A1AR) in the proximal tubule. Methylxanthines are weak renal vasodilators, and they act as competitive antagonists against adenosine-induced preglomerular vasoconstriction. Caffeine and theophylline stimulate the secretion of renin by inhibition of adenosine receptors and removal of the general inhibitory brake function of endogenous adenosine. Since enhanced intrarenal adenosine levels lead to reduced glomerular filtration rate in several pathological conditions theophylline has been tested for its therapeutic potential in the renal impairment following administration of nephrotoxic substances such as radiocontrast media, cisplatin, calcineurin inhibitors or following ischemia-reperfusion injury. In experimental animals functional improvements have been observed in all of these conditions, but available clinical data in humans are insufficient to affirm a definite therapeutic efficacy of methylxanthines in the prevention of nephrotoxic or postischemic renal injury.

Dietary factors and hypertension

There is increasing evidence that nutritional factors are critical in the pathogenesis of essential hypertension typical for acculturated societies. These factors include sodium, potassium, calcium, alcohol, and type and level of fat in the diet. More research is needed, however, before the role of various nutrients in the prevention and treatment of hypertension will be ascertained.

Genetics of coffee consumption and its stability

BACKGROUND

Coffee is a highly popular drink associated with the pathogenesis of several diseases and the use of tobacco and alcohol. Considering the worldwide consumption, coffee has a substantial effect on individual wellbeing and public health. The role of genetic factors contributing to interindividual differences and their stability in coffee use is not well known.

AIMS

We analysed the heritability of coffee consumption and its stability in a large population-based sample of Finnish twins.

DESIGN

In 1975 and 1981 a postal questionnaire on coffee consumption was sent to all Finnish same-sex twin pairs born before 1958. Responses were obtained from 10 716 complete twin pairs in 1975 (3409 monozygotic and 7307 dizygotic), of whom 8124 also responded in 1981. The data were analysed using classical twin modelling based on linear structural equations.

FINDINGS

Additive genetic and unique environmental factors affected coffee drinking, whereas shared environmental factors did not show any effect. Heritability of coffee consumption, adjusted for age and sex, was estimated as 0.56 in 1975 and 0.45 in 1981. Coffee consumption showed a moderate correlation between these two time-points (r = 0.58 in men and 0.55 in women). Genetic factors affecting coffee consumption were stable: additive genetic correlations were 0.84 in men and 0.83 in women, whereas unique environmental correlations were moderate (0.45 and 0.36). Additive genetic factors had the highest contribution in young adults.

CONCLUSIONS

Coffee consumption is affected by both additive genetic and unique environmental factors, each of which plays an almost equally important role. The long-term stability of coffee consumption is affected mainly by a stable set of additive genetic factors.

Coffee consumption and the incidence of antihypertensive drug treatment in Finnish men and women

BACKGROUND

Only 2 prospective studies have previously investigated the association between coffee consumption and incident hypertension, and the findings are equivocal.

OBJECTIVE

The objective was to determine the relation between coffee consumption and the incidence of antihypertensive drug treatment.

DESIGN

We prospectively followed 24 710 Finnish subjects aged 25-64 y without a history of antihypertensive drug treatment, coronary heart disease, or stroke at baseline. Daily coffee consumption was assessed by questionnaires.

RESULTS

During a mean follow-up period of 13.2 y, 2505 participants started antihypertensive drug treatment. The multivariate-adjusted (age, sex, study year, education, leisure-time physical activity, smoking, body mass index, high total cholesterol, history of diabetes, and alcohol, tea, fruit, vegetable, sausage, and bread consumption) hazard ratios for antihypertensive drug treatment associated with the amount of coffee consumed daily (0-1, 2-3, 4-5, 6-7, or >or=8 cups) were 1.00, 1.29 (95% CI: 1.09, 1.54), 1.26 (95% CI: 1.06, 1.49), 1.24 (95% CI: 1.04, 1.48), and 1.14 (95% CI: 0.94, 1.37) (P for trend = 0.024), respectively. This trend became marginally significant after additional adjustment for baseline systolic blood pressure (P for trend = 0.077).

CONCLUSIONS

The results indicate that coffee drinking seems to increase the risk of antihypertensive drug treatment, and this risk was higher in subjects with low-to-moderate coffee intakes; however, there was no significantly increased trend in drinkers of approximately 1 cup (100 mL)/d or >or=8 cups/d.

Is coffee a functional food?

Definitions of functional food vary but are essentially based on foods' ability to enhance the quality of life, or physical and mental performance, of regular consumers. The worldwide use of coffee for social engagement, leisure, enhancement of work performance and well-being is widely recognised. Depending on the quantities consumed, it can affect the intake of some minerals (K, Mg, Mn, Cr), niacin and antioxidant substances. Epidemiological and experimental studies have shown positive effects of regular coffee-drinking on various aspects of health, such as psychoactive responses (alertness, mood change), neurological (infant hyperactivity, Alzheimer's and Parkinson's diseases) and metabolic disorders (diabetes, gallstones, liver cirrhosis), and gonad and liver function. Despite this, most reviews do not mention coffee as fulfilling the criteria for a functional food. Unlike other functional foods that act on a defined population with a special effect, the wide use of coffee-drinking impacts a broad demographic (from children to the elderly), with a wide spectrum of health benefits. The present paper discusses coffee-drinking and health benefits that support the concept of coffee as a functional food.

Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials

PURPOSE

Coffee is a widely consumed beverage and small health effects of substances in coffee may have large public health consequences. It has been suggested that caffeine in coffee increases the risk of hypertension. We performed a meta-analysis of randomized controlled trials of coffee or caffeine and blood pressure (BP).

DATA IDENTIFICATION

BP trials of coffee or caffeine published between January 1966 and January 2003 were identified through literature databases and manual search.

STUDY SELECTION

A total of 16 studies with a randomized, controlled design and at least 7 days of intervention was selected, comprising 25 strata and 1010 subjects.

DATA EXTRACTION

Two persons independently obtained data on sample size, type and duration of intervention, changes in BP and heart rate (HR), and subjects' characteristics for each trial. Meta-analysis was performed using a random-effects model.

RESULTS

A significant rise of 2.04 mmHg [95% confidence interval (CI), 1.10-2.99] in systolic BP and 0.73 mmHg (95% CI, 0.14-1.31) in diastolic BP was found after pooling of coffee and caffeine trials. When coffee trials (n = 18, median intake: 725 ml/day) and caffeine trials (n = 7, median dose: 410 mg/day) were analysed separately, BP elevations appeared to be larger for caffeine [systolic: 4.16 mmHg (2.13-6.20); diastolic: 2.41 mmHg (0.98-3.84)] than for coffee [systolic: 1.22 mmHg (0.52-1.92) and diastolic: 0.49 mmHg (-0.06-1.04)]. Effects on HR were negligible.

CONCLUSIONS

Regular caffeine intake increases BP. When ingested through coffee, however, the blood pressure effect of caffeine is small.

[Effect of caffeine on myocardial blood flow during pharmacological vasodilation]

Pharmacologic stress with adenosine is frequently used for noninvasive detection of coronary artery disease. Dietary intake of caffeinated food, beverages or medications might alter adenosine-induced hyperemic blood flow, thereby compromising the diagnostic sensitivity of adenosine stress testing. In this case we report on a male patient with CAD. Myocardial blood flow at rest and during adenosine-induced hyperemia 2 hours after consumption of decaffeinated coffee and again without caffeine intake were quantified by ammonia PET. After caffeine intake there was a clearly diminished increase of myocardial blood flow during adenosine. The average coronary flow reserve in the myocardium was 1.3 after caffeine. In the baseline study without caffeine the coronary flow reserve has been improved to 2.3. Caffeine intake alters the coronary vasodilatory capacity. These findings emphasize the importance of carefully screening patients for intake of caffeinated food prior to adenosine stress testing.

Blood pressure response to caffeine shows incomplete tolerance after short-term regular consumption

Caffeine acutely raises blood pressure (BP). The clinical significance of this effect depends on whether BP responses persist in persons who consume caffeine on a daily basis. Accordingly, the ability of caffeine to raise BP after 5 days of regular daily intake was tested in a randomized controlled trial. Individual differences in tolerance formation were then examined. Men (n=49) and women (n=48) completed a double-blind, crossover trial conducted over 4 weeks. During each week, subjects abstained for 5 days from dietary caffeine and instead used capsules totaling 0 mg, 300 mg, and 600 mg of caffeine per day in 3 divided doses. On day 6, in the laboratory, they used capsules with either 0 mg or 250 mg of caffeine at 9:00 am and 1:00 pm. Systolic/diastolic BP increases as a result of 250 mg of caffeine remained significant (P<0.006/0.001) at all levels of previous daily consumption. Individual difference comparisons found that although half the subjects had complete loss of systolic and diastolic BP responses to the challenge doses, the other half showed no loss in BP response, even after using 600 mg of caffeine per day for the previous 5 days (F >7.90, P <0.001). The sexes did not differ in degree of tolerance formation. Daily caffeine consumption failed to eliminate the BP response to repeated challenge doses of caffeine in half of the healthy adults who were tested. Caffeine may therefore cause persistent BP effects in persons who are regular consumers, even when daily intake is at moderately high levels.

Acute effect of caffeine on arterial stiffness and aortic pressure waveform

Caffeine acutely increases blood pressure and peripheral vascular resistance, in part because of sympathetic stimulation. Its effects on large artery properties are largely unknown. In a double-blind crossover study, 7 healthy subjects 26+/-2.6 years of age (mean+/-SEM) were studied for 90 minutes while in the supine position on 2 occasions separated by a week in random order after ingestion of 250 mL caffeinated (150 mg) and decaffeinated (<2 mg) coffee. Compared with baseline, arterial stiffness measured by carotid femoral pulse wave velocity increased progressively from 7.2+/-0.41 to 8.0+/-0.6 m/s (P<0.05) at 90 minutes after caffeine intake, an effect that may be independent of changes in blood pressure. In addition, arterial wave reflection, measured by applanation tonometry from the aortic pressure waveform, also increased from -5.7+/-7.6% to 5.28%+/-5.6 (P<0.01). No such changes were seen with decaffeinated coffee intake. Although the integral of the brachial systolic and diastolic blood pressure values over the 90 minutes was larger (P<0.05) after caffeinated than decaffeinated coffee intake, the effect on aortic systolic and diastolic blood pressures was more pronounced (P<0.05) than on the brachial artery. These results show a significant effect of caffeine intake on arterial tone and function and suggest that caffeine acutely increases arterial stiffness.

Effects of coffee on ambulatory blood pressure in older men and women: A randomized controlled trial

This study assessed the effects of regular coffee drinking on 24-hour ambulatory blood pressure (ABP) in normotensive and hypertensive older men and women. Twenty-two normotensive and 26 hypertensive, nonsmoking men and women, with a mean age of 72.1 years (range, 54 to 89 years), took part in the study. After 2 weeks of a caffeine-free diet, subjects were randomized to continue with the caffeine-free diet and abstain from caffeine-containing drinks or drink instant coffee (5 cups per day, equivalent to 300 mg caffeine per day) in addition to the caffeine-free diet for a further 2 weeks. Change in systolic and diastolic blood pressures (SBP, DBP) determined by 24-hour ambulatory BP monitoring showed significant interactions between coffee drinking and hypertension status. In the hypertensive group, rise in mean 24-hour SBP was greater by 4.8 (SEM, 1.3) mm Hg (P=0.031) and increase in mean 24-hour DBP was higher by 3.0 (1.0) mm Hg (P=0.010) in coffee drinkers than in abstainers. There were no significant differences between abstainers and coffee drinkers in the normotensive group for 24-hour, daytime, or nighttime SBP or DBP. In older men and women with treated or untreated hypertension, ABP increased in coffee drinkers and decreased in abstainers. Restriction of coffee intake may be beneficial in older hypertensive individuals.

The best defense against hypoglycemia is to recognize it: is caffeine useful?

Caffeine, 1,3,7trimethylxanthine, is used by 80% of the adult population of the world in its various forms. Even the simple pleasure of consuming this socially acceptable drug has implications for the person with diabetes mellitus. Caffeine may increase an individual's sensitivity to hypoglycemia through the combined effects of reducing substrate delivery to the brain via constriction of the cerebral arteries, whilst simultaneously increasing brain glucose metabolism and augmenting catecholamine production. This article summarizes the evidence supporting the hypothesis that caffeine influences the perception of and physiological response to hypoglycemia. Under laboratory conditions, acute ingestion of caffeine markedly enhances the symptomatic and sympathoadrenal responses to hypoglycemia in both healthy volunteers and patients with type 1 diabetes. Recently a study of free-living people with type 1 diabetes showed that caffeine consumption increased the awareness of hypoglycemia. Caffeine has been associated with a number of negative effects and addiction. Most serious of these associations are ischemic heart disease and hypertension, the relationships have not been clearly established and the evidence to date is controversial. Thus we conclude that in modest doses, caffeine may be a useful adjuvant therapy for patients with hypoglycemia unawareness. For once here is a therapy which is inexpensive, safe, and remarkably popular with its consumers.

Acute blood pressure elevations with caffeine in men with borderline systemic hypertension

Whether the vasoconstrictive actions of caffeine are enhanced in hypertensive persons has not been demonstrated. Thus, caffeine (3.3 mg/kg) versus placebo was tested in 48 healthy men (aged 20 to 35 years) selected after screening on 2 separate occasions. Borderline hypertensive men (n = 24) were selected with screening systolic blood pressure (BP) of 140 to 160 mm Hg and/or diastolic BP 90 to 99 mm Hg. Low-risk controls (n = 24) reported no parental history of hypertension and had screening BP < 130/85 mm Hg. Participants were then tested on 2 occasions after 12-hour abstinence from caffeine in each of 2 protocols; this required a total of 4 laboratory visits. Caffeine-induced changes in diastolic BP were 2 to 3 times larger in borderline subjects than in controls (+8.4 vs +3.8 mm Hg, p < 0.0001), and were attributable to larger changes in impedance-derived measures of systemic vascular resistance (+135 vs +45 dynes.s.cm-5, p < 0.004). These findings were consistent and reached significance in both protocols. The percentage of borderline subjects in whom diastolic BP changes exceeded the median control response was 96%. Consequently, whereas all participants exhibited normotensive levels during the resting predrug baseline, 33% of borderline subjects achieved hypertensive BP levels after caffeine ingestion. Thus, in borderline hypertensive men, exaggerated responses to caffeine were: selective for diastolic BP, consistent with greater vasoconstriction, replicated in 2 protocols, and representative of nearly all borderline hypertensives. We suspect that the potential for caffeine to stabilize high resistance states in susceptible persons suggests that its use may facilitate their disease progression, as well as hinder accurate diagnosis and treatment.

Coffee: brew or bane?

Coffee is the most commonly used drug in the United States. The medical literature is conflicted regarding the harmful effects of coffee and caffeine. Because the articles that have appeared are so different, a formal meta-analysis is not the ideal way to summarize the data. However, this literature review suggests that coffee does not have an appreciable effect on hyperlipidemia, hypertension, ischemic heart disease, or cancer. The effects of decaffeinated coffee are much less well-defined, and there is little rationale for recommending that patients switch to decaffeinated coffee. A less appreciated problem with caffeine is that it may increase the risk of osteoporosis and hip fracture.

Effects of cessation of caffeinated-coffee consumption on ambulatory and resting blood pressure in men

Coffee consumption has been weakly linked to high blood pressure (BP). The hypothesis that cessation of caffeinated-coffee consumption lowers ambulatory BP was tested in men in a randomized trial. One hundred eighty-six middle-aged, normotensive, male, habitual caffeinated-coffee consumers were recruited. Of these subjects, 150 had sufficiently complete, ambulatory BP measurements for analysis. After 2 months of standard caffeinated-coffee consumption, subjects were randomized to consume an equal amount of the same standard caffeinated coffee or a standard decaffeinated coffee, or to discontinue coffee consumption for 2 months. Diet composition, body weight and exercise did not change. Resting BP and heart rate were not different between the groups before and after intervention. In comparison with the continued caffeinated-coffee group (control), the decaffeinated-coffee group revealed significant reductions in mean ambulatory systolic BP during the morning (-4.0 +/- 11 mm Hg; p = 0.014), afternoon (-5.3 +/- 10 mm Hg; p = 0.001) and evening (-3.2 +/- 10 mm Hg; p = 0.003) hours, reductions in mean ambulatory diastolic BP during the afternoon (-1.8 +/- 10 mm Hg; p = 0.063) and evening (-1.8 +/- 10 mm Hg; p = 0.059) hours and no change in ambulatory heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Caffeine attenuates the renal vascular response to angiotensin II infusion

Non-modulation has been proposed as an intermediate phenotype in human essential hypertension. The trait is characterized by blunted aldosterone and renal plasma flow responses to short-term angiotensin II (Ang II) infusion. Elevated tissue Ang II levels or decreased tissue adenosine levels could account for this decreased sensitivity to Ang II. In support of the latter possibility, endogenous adenosine has been shown to contribute to the renal vasoconstrictive response to Ang II in animals. We therefore tested the hypothesis that endogenous adenosine contributes to modulation of renal plasma flow in sodium-replete humans. We examined the effect of long-term administration of the adenosine receptor antagonist caffeine on baseline renal plasma flow and on the renal plasma flow response to short-term Ang II infusion in six salt-replete normotensive subjects in a single-blind, placebo-controlled study. para-Aminohippurate clearance was used to assess renal plasma flow. Ang II was infused in graded doses (0.3 to 3 ng/kg per minute) in the presence and absence of caffeine (250 mg PO TID for 7 days). Blood pressure, plasma renin activity, Ang II, electrolytes, and para-aminohippurate clearance were measured before and after each dose of Ang II. Caffeine did not alter either baseline blood pressure or the blood pressure response to Ang II but did increase baseline plasma renin activity from 0.72 +/- 0.09 to 1.42 +/- 0.26 ng angiotensin I/mL per hour (P = .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of coffee on ambulatory blood pressure in patients with treated hypertension

Effects of caffeine on ambulatory blood pressure, heart rate, renin-angiotensin system, and ANP were studied in patients treated for mild to moderate hypertension in a randomized, double-blind, placebo-controlled, cross-over trial comparing 2 weeks of caffeine-free diet with 2 weeks of regular coffee use. Twenty-three patients (13 men; aged 28-74 years) with treated, mild to moderate essential hypertension and a regular intake of 3-4 cups of coffee daily completed the study. Mean 24-h, day- or night-time ambulatory blood pressure and heart rate were not different between regimens. Nor were there any effects on the renin-angiotensin system while ANP was significantly increased during caffeine intake. Compliance of the dietary regimen was excellent as assessed by serum caffeine concentration measurements. We conclude that habitual coffee drinking did not influence the 24-h blood pressure profiles or cardiovascular hormones in treated hypertensives.

Effect of caffeine treatment on plasma renin activity and angiotensin I concentrations in rats on a low sodium diet

Animals treated acutely with an adenosine receptor antagonist have elevated plasma renin activity. This observation suggests that endogenous adenosine plays a physiologically significant role in restraining renin release. However, it is unclear whether chronic blockade of adenosine receptors would cause a rise of renin activity since tolerance to adenosine blockade is known to develop quickly. An earlier study partially addressed this question by showing that chronic blockade of adenosine receptors with caffeine exacerbated both the rise of plasma renin activity and the decline of renal function in 2-kidney-1-clip (2K1C) renovascular hypertensive rats. However, that study did not determine whether the difference in renin activity occurred solely as a secondary result of the difference in renal function. The purpose of this study was to reexamine the effect of chronic caffeine consumption on plasma renin activity and angiotensin I levels in animals in another high-renin model, i.e., the low sodium diet. The low sodium diet is devoid of the potential confounding effect of deteriorating renal function associated with the 2K1C renovascular hypertension model. In this study, animals received normal rat chow and drank either 0.1% caffeine water or vehicle for ten days. After ten days, all rats were switched to a low sodium diet for three weeks. Plasma renin activity and plasma angiotensin I levels were measured before, and at 1 and 3 weeks after initiating the low sodium diet. The results of this study show that chronic blockade of adenosine receptors with 0.1% caffeine water increases plasma renin activity and angiotensin I concentration before and throughout the three weeks when animals were on the low sodium diet. The results of this study suggest that the inhibitory role of adenosine on renin release is a general physiological process, rather than a special situation applicable only to the 2K1C model.

Contrasting excitatory and inhibitory effects of adenosine in blood pressure regulation

Administration of adenosine results in profound hypotension without the expected activation of reflex sympathetic and renin mechanisms in most animal models. This action can be explained by the vasodilatory and neuroinhibitory effects of adenosine. It is generally considered an inhibitory neuromodulator because it inhibits the release of virtually all neurotransmitters studied and produces hyperpolarization of neurons. In contrast, adenosine produces vasoconstriction of some vascular beds, including the renal and pulmonary circulations. Renal vasoconstriction is caused by activation of A1 receptors and involves an interaction with angiotensin II. In other vascular beds adenosine releases eicosanoids, including thromboxane, also resulting in vasoconstriction. Adenosine-induced vasoconstriction is transient and species dependent. Neither the receptor type, the molecular mechanisms of these actions, nor their significance to pathophysiological processes have been defined. Adenosine also has an apparent excitatory effect in the nucleus tractus solitarii. Microinjections of adenosine into this brain stem nucleus lead to decreased sympathetic tone and hypotension similar to those produced by the excitatory amino acid glutamate. The mechanism that explains this action has recently been explored and involves the release of glutamate by adenosine. Adenosine also stimulates afferent fibers mediating sympathetic activity, including renal and myocardial afferent nerves, and carotid and aortic chemoreceptors. Afferent nerve activation seems to be more pronounced in humans and may explain most of the cardiovascular and respiratory actions of adenosine in this species. Finally, animal studies suggest that endogenous adenosine plays a role in the regulation of the baroreceptor reflex and restrains the full expression of renin-dependent hypertension.

Caffeine restriction: effect on mild hypertension

OBJECTIVE

To determine the effects on blood pressure of modifying dietary caffeine intake in patients with mild and borderline hypertension by monitoring ambulatory and clinic blood pressure.

DESIGN

Four way, randomised, crossover trial of four consecutive two week dietary regimens: normal diet, caffeine free diet alone, caffeine free diet with decaffeinated instant coffee, caffeine free diet with caffeinated instant coffee (instant coffee phases conducted double blind).

SETTING

Hospital hypertension clinic, Scotland.

PATIENTS

52 patients (23 men; aged 26-67 years) with untreated borderline or mild hypertension (diastolic blood pressure 90-105 mm Hg) who normally drank a minimum of three cups of coffee daily.

MAIN OUTCOME MEASURES

Mean ambulatory blood pressure over 24 hours; mean morning, daytime, and night time ambulatory blood pressure; sitting clinic blood pressure at 1700; plasma caffeine concentration at 1700 on the last day of each regimen.

RESULTS

Mean 24 hour ambulatory blood pressure was not different between regimens. There was no difference in blood pressure variability between regimens. During the caffeine free diet alone morning ambulatory diastolic blood pressure was higher (2.8 mm Hg) than during the caffeine free diet with caffeinated coffee. Mean sitting clinic systolic blood pressure was higher at 1700 (4.7 mm Hg) with a caffeine free diet than with the caffeine free diet with caffeinated coffee (p less than 0.05). Dietary compliance as assessed by plasma caffeine concentration was excellent. There was no significant correlation between plasma caffeine concentration and blood pressure.

CONCLUSIONS

Drinking caffeinated instant coffee over a two week period does not adversely influence blood pressure in patients with borderline or mild hypertension; abstinence is of no benefit.

Boiled coffee and blood pressure. A 14-week controlled trial

The question of whether long-term elimination of coffee from the diet lowers blood pressure has not been settled. Consumption of Scandinavian-style "boiled coffee" is associated with coronary heart disease. However, little is known about the effect of brewing method on the blood pressure-raising potential of coffee. We have studied the effects on blood pressure and heart rate of total elimination of coffee and tea in comparison with drinking boiled coffee consumed as such, or boiled coffee consumed after filtration through paper filter. Thirty-one women and 33 men first consumed 6 cups/day of boiled and filtered coffee for 17 days. Then they were randomly divided into three groups, which for the next 79 days received either unfiltered boiled coffee (caffeine content 860 mg/l), boiled-and-filtered coffee (887 mg caffeine/l), or no coffee, the latter being replaced by fruit juice and mineral water. Total elimination of coffee did not significantly affect blood pressure or heart rate relative to boiled-and-filtered coffee. In subjects who drank boiled coffee, mean ambulant systolic blood pressure rose significantly relative to those who consumed boiled-and-filtered coffee (mean difference +/- SEM, 3.1 +/- 1.1 mm Hg, p = 0.006). This response showed a tendency to be stronger for women (4.5 +/- 1.8 mm Hg) than for men (1.7 +/- 1.2 mm Hg). We conclude that elimination of filtered coffee has no substantial long-term effect on blood pressure, but consumption of unfiltered boiled coffee may cause a slight but significant rise in systolic blood pressure.

Effects of caffeine on pressor regulation during rest and exercise in men at risk for hypertension

Caffeine-induced blood pressure elevations are well documented in habitual consumers, occurring through both vasoconstrictive and cardiostimulatory actions. Whether caffeine hinders pressor regulation during exercise has been uncertain, particularly in those at risk for hypertension. Thus effects of caffeine versus placebo were studied during supine bicycle exercise in healthy men (ages 20 to 35). Hypertension risk was defined during screening: high risk (HRISK) = 135 to 154/85 to 94 mm Hg plus parental hypertension (n = 20); low risk (LRISK) = less than or equal to 132/84 mm Hg and no parental hypertension (n = 14). Exaggerated pressor responses (greater than or equal to 230/100 mm Hg) seen during exercise after placebo identified a subgroup of seven HRISKs indistinguishable at rest from the remaining HRISK men. This subgroup showed a larger resting diastolic response to caffeine (p less than 0.05) than LRISKs and other HRISKs. Compared with placebo, caffeine increased the number of LRISK (0% to 36%) and HRISK (35% to 50%) men reaching abnormal exercise blood pressures, and blunted normal increments in cardiac index at higher workloads among HRISK men (p = 0.05). Thus restriction of caffeine before exercise might benefit persons with either risk for hypertension or unusual sensitivity to caffeine.

Effects of caffeine with repeated dosing

We have recently demonstrated dose-dependency of caffeine metabolism under multiple dosing conditions. Whether there are persistent pharmacodynamic actions of caffeine under such circumstances is the focus of this report. Nine healthy subjects were given, in randomized 5 day blocks, placebo, 4.2 (low) and 12 (high) mg.kg-1.day-1 of caffeine in 6 divided doses. After 5 days, complete tolerance developed to the effects of caffeine on blood pressure, heart rate and plasma glucose concentrations. The 24-h area under the curve (AUC) for plasma norepinephrine and the AUC for the total sum of free fatty acids (FFA) both demonstrated a trend to increase with the high dose caffeine treatment. When the AUC for norepinephrine was split into 12 h time periods, a significant difference between the placebo and the high dose treatment block was seen. We conclude that regular consumption of 12 mg.kg-1 of caffeine per day (equivalent to approximately 6 to 11 cups of coffee per day) may produce pharmacodynamic effects not completely compensated for by the development of tolerance. Mechanisms of tolerance may be overwhelmed by the nonlinear accumulation of caffeine and other methylxanthines in the body when caffeine metabolism becomes saturable.

The effect of caffeine on postprandial hypotension in the elderly

In a double-blind, randomized trial the effects of caffeinated and decaffeinated drinks on postprandial hemodynamic and neurohumoral changes were studied in seven fit, elderly subjects after a standard 2.4MJ meal. There was a significant difference in supine postprandial systolic blood pressure between the placebo and caffeine phases (P less than 0.01); at 60 minutes, supine systolic blood pressure had fallen 14 mmHg [95% confidence interval (CI)-7 to-21 mmHg, p less than 0.01) after placebo, but was unchanged after caffeine (+9 mmHg, CI 0 to 18 mmHg, NS]. Similar differences between placebo and caffeine were seen in erect systolic and diastolic blood pressure (P less than 0.01), although orthostatic tolerance was maintained throughout each study period. Postprandial plasma noradrenaline levels were higher (P less than 0.02) and the increase greater (P less than 0.02) after caffeine than after placebo. Caffeine administered at the end of a standard test meal prevents the postprandial fall in blood pressure in fit, elderly subjects. The clinical relevance of this finding has yet to be determined, but it may offer a simple remedy for patients with symptomatic postprandial hypotension.

Coffee and coronary heart disease: a review

Since the early 1900s, coffee has been implicated as having adverse effects on human health. Recent attention has focused on coffee's relation to CHD, but because of conflicting results of epidemiologic studies on coffee and CHD mortality, attention has turned to the effects of coffee and caffeine on individual CHD risk factors. Coffee's effect on serum lipids does not appear to be due to caffeine. If in fact an adverse effect on lipids exists, it may be related to other factors including biochemical constituents other than caffeine, hardness of the water used in preparation, and the method of preparation, filtered coffee having no effect. The data are fairly convincing that chronic coffee ingestion does not induce hypertension, although acute consumption produces a small, short-lived increase in BP. The least well understood effect of coffee is its potential to induce cardiac arrhythmias, including potentially lethal ventricular ectopy in certain individuals. More work is needed in this area of arrhythmias before any concrete recommendations can be made. Until more convincing evidence against coffee is compiled, it appears that, at least in moderate amounts in otherwise healthy persons, coffee is a safe beverage.

Effect of decaffeinated versus regular coffee on blood pressure. A 12-week, double-blind trial

The effect of decaffeinated versus regular coffee on blood pressure and heart rate was investigated. In a randomized double-blind, crossover trial, 45 healthy volunteers (23 women and 22 men, 25-45 years old) with a habitual intake of 4-6 cups coffee/day received 5 cups of regular coffee each day for a period of 6 weeks, and 5 cups of decaffeinated coffee for the next 6 weeks or vice versa. The background diet was kept constant. The total amount of caffeine ingested was 40 mg during the decaffeinated coffee period and 445 mg during the regular coffee period. Use of decaffeinated coffee led to a significant but small decrease in systolic (mean +/- SEM, -1.5 +/- 0.4 mm Hg; p = 0.002) and diastolic (-1.0 +/- 0.4 mm Hg; p = 0.017) ambulant blood pressure and to a small increase in ambulant heart rate (+1.3 +/- 0.6 beats/min; p = 0.031). Individual differences in rate of caffeine metabolism did not explain differences in long-term response of blood pressure to caffeine. We conclude that in normotensive adults replacement of regular by decaffeinated coffee leads to a real but small fall in blood pressure. However, it remains to be established whether a mass switch from regular to decaffeinated coffee would significantly reduce the total incidence of hypertension-related disorders.

University of California, Davis, conference: Mild hypertension

Prevalence of "higher than normal" blood pressures in a community is inversely related to the magnitude of the elevation; the milder grades of elevation are far more prevalent. A multifactorially inherited tendency to develop hypertension is modulated by multiple environmental influences. Autonomic nervous and behavioral factors plausibly appear to contribute to the initiating mechanisms of hypertension; the associated hemodynamic changes and the resulting cardiovascular structural changes interact to perpetuate the process. The complex interaction of hypertension and atherosclerosis is further complicated by direct as well as secondary effects of antihypertensive drugs on atherogenesis. Attributable cardiovascular risk is generally proportional to the degree of hypertension across the entire range of elevated blood pressure; this kind of relationship holds also for normal versus subnormal blood pressure values. Pharmacologic lowering of blood pressure, however, does not confer proportional benefit. Thus, such lowering of blood pressure to normotensive levels does not reduce the risk level to that in the normotensive population. Therapeutic outcome is influenced by the interaction of blood pressure lowering, type of antihypertensive agents used, existing risk factors, and target organ damage. Benefits of lowering blood pressure in established mild hypertension (diastolic blood pressure greater than 95 mm Hg) are confirmed. Drug treatment of patients with lower diastolic blood pressure or with isolated elevations of systolic blood pressures continues to be controversial as does the choice of initial therapeutic agent(s). The large-scale experience of clinical trials encompassing the long-term risks and benefits of the drug treatment of mild hypertension is limited to the use of diuretics and adrenergic beta blockers. A variety of new and promising therapeutic agents for use as alternate choices for initial therapy needs to undergo comparative evaluation.

Methylxanthines: toxicity to humans. 2. Caffeine

While there are several comprehensive reviews on the toxic effects of methylxanthines in animals, data on the toxicity of these chemicals in humans has not been extensively reviewed in one document. In a previous paper (Stavric, Fd Chem. Toxic. 1988, 26, 541), the toxicity of theophylline was reviewed. This paper, the second of three, is intended to provide an overview of the human toxicity of caffeine. Only pertinent and recent information on caffeine toxicity is summarized. In addition, some information regarding the benefits of caffeine and the mechanism of its effects is also provided. The use, effects and toxicity of caffeine intake are reviewed separately for different segments of the population. Controversy concerning the possible association of caffeine with fibrocystic disease of the breast and over the behavioural effects of the drug is presented briefly.