Sex differences in the hemodynamic responses to mental stress: Effect of caffeine consumption

How Long Is Long Enough? Controlling for Acute Caffeine Intake in Cardiovascular Research

Caffeine substantially affects cardiovascular functioning, yet wide variability exists in caffeine control procedures in cardiovascular reactivity research. This study was conducted in order to identify a minimal abstention duration in habitual coffee consumers whereby cardiovascular reactivity is unconfounded by caffeine; Six hours (caffeine's average half-life) was hypothesized. Thirty-nine subjects (mean age: 20.9; 20 women) completed a repeated measures study involving hand cold pressor (CP) and memory tasks. Caffeinated and decaffeinated coffee were administered. The following cardiovascular indices were acquired during pre-task, task, and post-task epochs prior to coffee intake, 30 min-, and six hours post-intake: Heart rate (HR), high-frequency heart rate variability (HF-HRV), root mean squared successive differences (RMSSD), systolic and diastolic blood pressures (SBP, DBP), mean arterial pressure (MAP), pre-ejection period (PEP), left ventricular ejection time (LVET), systemic vascular resistance (SVR), systemic vascular resistance index (SVRI). Results support the adequacy of a six-hour abstention in controlling for caffeine-elicited cardiovascular changes. The current study offers a suggested guideline for caffeine abstention duration in cardiovascular research in psychophysiology. Consistent practice in caffeine abstention protocols would promote validity and reliability across such studies.

Effects of Low Dose Caffeine on Post-Exercise Heart Rate Variability: A Double-Blind Placebo-Controlled Trial

Caffeine may impact post-exercise heart rate variability (HRV); although, studies have yielded inconsistent findings. We examined the effects of low dose caffeine on post-exercise HRV. Healthy, college-aged adults [n = 18; age: 22.1 ± 2.6 years; BMI: 26.9 ± 4.3 kg/m2; estimated maximal oxygen consumption (VO2max): 45.1 ± 8.3 ml·kg-1·min-1] participated in a repeated-measures, double-blind, placebo-controlled trial. During the experimental trials, participants were fitted with a heart rate monitor and a mouthpiece with a one-way nonrebreathing valve and then rested for 10 min during baseline HRV and expired gas assessments. Participants chewed either caffeine (~170mg) or placebo gum for 5 min. Following expectoration and a 5 min warmup, participants walked on a treadmill for 20 min at 60% of estimated VO2max and then rested for 30 min. HRV indices were calculated from 10 min measurements during baseline and post-exercise (post 1, 2, and 3). A main effect of treatment was found for standard deviation of RR intervals (SDNN), absolute power of low frequency band (LF), absolute power of high frequency band (HF), and the standard deviation perpendicular to the line-of-identity in Poincaré plot (SD1) (p < 0.05). Further, a trend for higher root mean square of successive RR interval differences (RMSSD) with caffeine was observed (p = 0.066). Post hoc t-tests revealed that post-exercise SDNN, LF, HF, and SD1 were higher with caffeine compared to placebo (p ≤ 0.012). Results demonstrated that low dose caffeine did not delay the recovery of HRV indices reflective of parasympathetic nervous system activity following an acute bout of moderate exercise.

Controlling for caffeine in cardiovascular research: A critical review

Caffeine, the most widely consumed drug in the world, exerts numerous effects on cardiovascular activity. Thus, it is important and advisable to control for caffeine consumption in studies examining caffeine and/or cardiovascular activity and reactivity. This paper 1) reviews the literature concerning caffeine's effects on cardiovascular parameters; 2) summarizes the widely varying protocols used to control for the drug in extant cardiovascular literature, and 3) provide guidelines for caffeine control procedures to minimize potentially confounding acute and withdrawal effects of the drug. An abstention period equal to the average half-life of the drug is recommended for creation of methodological controls for caffeine. Additional methodological recommendations are described concerning factors that moderate the half-life of caffeine. When feasible, researchers should consider and aim to control for caffeine's acute and extended psychophysiological effects. This understudied issue has fundamental implications for caffeine-related investigations and research in psychophysiology and behavioral medicine.

Caffeine increases parasympathetic reactivation without altering resting and exercise cardiac parasympathetic modulation: A balanced placebo design

The sympathicotonic effect of caffeine is strongly evidenced in the literature. However, the effects of caffeine or caffeine expectancy on the cardiac parasympathetic modulation remain obscure. Thus, the aim of this study was to investigate the effects of caffeine consumption and expectancy of caffeine consumption on the cardiac parasympathetic modulation under different stress conditions. Twenty-one physically active men (22.3 ± 2.9 years, 25.2 ± 2.7 kg/m²) consumed ∼3 mg/kg of caffeine received as caffeine, caffeine as placebo, placebo as placebo and placebo as caffeine. Parasympathetic modulation was assessed by heart rate variability (HRV-Poincaré SD1 index) at supine and orthostatic positions, during a submaximal exercise (HRV threshold-HRV_T) and during each 60 seconds (s) within 300 s of post-exercise active recovery. A factorial ANOVA for repeated measures (p < 0.05) was used to assess the effect of caffeine, expectancy and resting time after caffeine intake on the HRV. No significant effect of caffeine or expectancy was observed on the SD1 value at supine or standing positions (p = 0.47-0.53; p = 0.57-0.31, respectively), despite an increase in this variable after resting periods in both positions (p < 0.001). During exercise, caffeine and expectancy do not alter the HRV_T (p = 0.51-0.39). However, higher SD1 values were observed after caffeine administration from 60 to 300 s post-exercise recovery (p = 0.01-0.05) but not for the effects of expectancy (p = 0.19-0.94). We concluded that low doses of caffeine or expectancy do not alter the resting cardiac parasympathetic modulation or HRV_T. However, caffeine, but not expectancy, increases parasympathetic reactivation after a submaximal exercise test in young men.

Pulse arrival time measurement with coffee provocation

This study investigated the effect of coffee intake in pulse arrival time (PAT) and pulse wave velocity (PWV) measured with electrocardiogram (ECG) from arms and photoplethysmogram (PPG) from fingertip. In addition, correlation of PWV with blood pressure (BP) is analyzed. 30 healthy participants were recruited to two measurement sessions, one arranged before and another one after the coffee intake. During each session, ECG and PPG were measured continuously for six minutes and PAT values calculated from ECG R-peak to the maximum of the first derivative of the PPG pulse. In addition, blood pressure was measured twice during each session with cuff based method. Coffee intake had statistically significant influence on both systolic and diastolic blood pressure, but not on PAT or PWV. Correlation between systolic blood pressure and PWV was 0.44. Individual calibration, additional derivatives of ECG and PPG such as heart rate, pulse pressure, or waveform characteristics could improve the correlation.

Ever at the ready for events that never happen

Stress, whether daily stress, work stress or traumatic stress, is unhealthy. This lecture covers three recent theoretical approaches in explaining the mechanisms underlying the influence of psychological stress on somatic health. It is argued that stress research should focus less on stressors themselves and put more emphasis on prolonged stress responses. Three mechanisms are identified that cause this unhealthy prolonged stress response: first, the partly-proven mechanism of perseverative cognition; second, the mechanism of unconscious stress, which is currently being explored; and third, the notion of the stress response being a default response that is inhibited only when safety is perceived. All three mechanisms are deeply rooted in millions of years of our evolution. Although the dangers of the past have virtually disappeared, many of us remain ever at the ready for events that never happen.

Acute effects of coffee consumption on self-reported gastrointestinal symptoms, blood pressure and stress indices in healthy individuals

Background

It has been suggested that coffee may affect the gut-brain axis with conflicting outcomes. Moreover, there is insufficient evidence to determine whether the type or temperature of coffee consumed will have a different impact on the gut-brain axis. The purpose of this study was to investigate the effects of acute coffee consumption on the following: 1. self-reported GI symptoms and salivary gastrin, 2. stress indices [salivary cortisol and alpha-amylase (sAA)] and psychometric measures, and 3. blood pressure (BP), in healthy, daily coffee consuming individuals in non-stressful conditions.

Methods

This was a randomized, double blind, crossover clinical trial, in which 40 healthy individuals (20 men, 20 women), 20–55 years of age, randomly consumed four 200 ml coffee beverages containing 160 mg caffeine (hot and cold instant coffee, cold espresso, hot filtered coffee), 1 week apart. Salivary samples and psychometric questionnaires were collected at baseline and post-coffee consumption at 15,30, and 60 min for salivary gastrin and sAA measurements and at 60,120, and 180 min for cortisol measurements. BP was measured at beginning and end of each intervention. ClinicalTrials.gov ID: NCT02253628

Results

Coffee consumption significantly increased sAA activity (P = 0.041), with significant differences only between cold instant and filter coffee at 15 and 30 min post-consumption (P < 0.05). Coffee temporarily increased salivary gastrin, without differences between coffee types. Coffee did not affect salivary cortisol or self-reported anxiety levels. Coffee consumption significantly increased BP, within the healthy physiological levels, in a gender specific manner at the end of the experimental periods, without differences between coffee types.

Conclusion

Acute coffee consumption in non-stressful conditions activated sAA and BP but not salivary cortisol, indicating activation of the sympathetic nervous system. Post-coffee sAA increase without a concomitant cortisol increase may also indicate that coffee may have some anti-stress properties.

Caffeine and physical training: effects on cardiac morphology and cardiovascular response

Objective to analyze the morphological structure of cardiac, blood pressure (BP), heart rate (HR) and heart rate variability (HRV) of rats subjected to physical training with supplementation of caffeine. Methods 60 rats were divided into 4 groups: control (CO), control with caffeine (CAF), trained control (TRE) and trained with caffeine (TCAF). All trained groups underwent 4 weeks of swimming, and all caffeine groups were supplemented by voluntary ingestion of caffeine diluted in drinking water. Results there were no changes to BP and HR between groups. Regarding HRV, there was a decrease in LFnorm (low frequency) and LF/HF ratio (low and high frequency) in TCAF and CAF compared to group (p<0.02 and p<0.03, respectively). An increase occurred in CAF compared to the CO in the component LFnorm (p<0.05). The results also showed an increase in the relative weight of heart in the TRE (p<0.04) and TCAF (p<0.03) compared to CO. Conclusion caffeine did not modify the hemodynamic responses. However, physical training resulted in a decrease in sympathetic response and an increase in relative heart weight.

Effects of caffeine and stress on biomarkers of cardiovascular disease in healthy men and women with a family history of hypertension

The connection between caffeine and its potentially detrimental effects on blood markers of cardiovascular disease (CVD) are controversial. Most studies have focused on cholesterol as a putative mediator of the caffeine-CVD relationship. Other blood markers such as C-reactive protein (CRP) and fibrinogen have been understudied. We examined the effects of caffeine and psychological stress on these CVD markers in healthy, young men and women with a confirmed family history of hypertension. A total of 52 normotensive, healthy adults (26 men and 26 women) aged 18-29 years (21.4 ± 0.3) participated in a laboratory session to examine stress reactivity following caffeine consumption. All participants had normal cholesterol levels. Blood pressure (BP), heart rate, serum cortisol and CRP and plasma fibrinogen were collected. Men and women administered caffeine displayed an additional increase in systolic BP and cortisol response to the stressor (p < 0.05). Stress interacted with caffeine and sex to alter cortisol, fibrinogen and systolic BP but not CRP levels. These results may shed light on sex-specific pathways that associate caffeine with CVD.

Effects of estrogen and opioid blockade on blood pressure reactivity to stress in postmenopausal women

Estrogen may influence coronary heart disease risk in women through the effects of endogenous opioids on autonomic control of blood pressure. In a randomized, placebo-controlled trial, we examined the combined effects of estrogen and the opioid antagonist, naltrexone, on blood pressure responses to psychological stress in 42 postmenopausal women. After 3 months of estrogen or estrogen plus progestin (hormone replacement therapy; n = 27) or placebo replacement, participants completed a mental arithmetic task after administration of .7 mg/kg oral naltrexone or placebo. Systolic blood pressure (SBP), diastolic blood pressure, mean arterial pressure and heart rate (HR) were measured at rest and during the arithmetic stressor. Stress produced significant increases in circulatory measures regardless of estrogen condition or opioid blockade (p's < .001). Interestingly, there was an estrogen by naltrexone interaction on SBP reactivity scores [F(1,38) = 4.36, p < .05], where women on estrogen with intact opioid receptors showed the largest SBP responses to stress, compared with all other conditions. This is consistent with some studies of premenopausal women, suggesting that estrogens may alter opioid function during stress. The interaction between estrogen and endogenous opioids may explain sex differences in opioid effects on stress reactivity in younger premenopausal women.

Caffeine and blood pressure response: sex, age, and hormonal status

PURPOSE

The pressor effect of caffeine has been established in young men and premenopausal women. The effect of caffeine on blood pressure (BP) remains unknown in postmenopausal women and in relation to hormone replacement therapy (HRT) use.

MATERIALS AND METHODS

In a randomized, 2-week cross-over design, we studied 165 healthy men and women in 6 groups: men and premenopausal women (35-49 yrs) vs. men and postmenopausal women (50-64 yrs), with postmenopausal women divided into those taking no hormone replacements (HR), estrogen alone, or estrogen and progesterone. Testing during one week of the study involved 6 days of caffeine maintenance at home (80 mg, 3x/day) followed by testing of responses to a challenge dose of caffeine (250 mg) in the laboratory. The other week involved ingesting placebos on maintenance and lab days. Resting BP responses to caffeine were measured at baseline and at 45 to 60 min following caffeine vs placebo ingestion, using automated monitors.

RESULTS

Ingestion of caffeine resulted in a significant increase in systolic BP in all 6 groups (4 +/- .6, p < 0.01). Diastolic BP significantly increased in response to caffeine in all (3 +/- .4, p < 0.04) but the group of older men (2 +/- 1.0, p = 0.1). The observed pressor responses to caffeine did not vary by age.

CONCLUSIONS

Caffeine resulted in an increase in BP in healthy, normotensive, young and older men and women. This finding warrants the consideration of caffeine in the lifestyle interventions recommended for BP control across the age span.

Sex differences in reinforcing value of caffeinated beverages in adolescents

Caffeine use is increasing among children and adolescents, but the effects of caffeine use on behavior and physiology within this population remain understudied and poorly understood. The purpose of this study was to test the hypothesis that adolescents find caffeinated soda more reinforcing than noncaffeinated soda and that this would be related to the level of usual caffeine consumption and to sex. We measured operant responding for portions of caffeinated and noncaffeinated soda at baseline and after daily consumption of 32 oz of caffeinated and noncaffeinated soda for 1 week each in 12-17-year-old participants. Participants also completed a behavioral checklist, a beverage-liking questionnaire, and a 24-h dietary recall to assess the energy intake at baseline and again after each week of beverage consumption. There was no difference in reinforcing value of noncaffeinated or caffeinated soda as a function of usual caffeine consumption. However, males found the caffeinated soda significantly more reinforcing than did females after the exposure period. To our knowledge, this is the first study to show a sex difference in the reinforcing value of caffeinated soda. These data suggest that boys may be more susceptible to the reinforcing effects of caffeine.

[Sympatho-vagal balance and cardiac response to mental challenge]

BACKGROUND

Based on functional relations between the central autonomic network and cortical areas involved in motivational, attentional, affective, and executive function, autonomic regulation can mediate cognitive performance as well as cardiovascular and psychosomatic diseases. Our objective was to test the predictive value of resting heart rate variability (HRV), a measure of sympatho-vagal balance, with regard to the type and intensity of cardiovascular responses to mental challenge.

MATERIALS AND METHODS

A total of 248 healthy subjects (85 females, aged 47.3+/-7.6 years; 163 males, aged 47.5+/-6.7 years) were included in the study. All participants underwent standardized psychometric testing (e.g., Stroop's color-word-conflict test).

RESULTS

First, we found significant increases of heart rate and sympatho-vagal balance (low frequency/high frequency) and significant decreases of absolute LF- and HF-power in response to mental tasks. Second, there were significant differences in cardiovascular response to mental challenge when clustering our population on the basis of sympatho-vagal balance at rest.

CONCLUSIONS

We conclude that short-term recordings of HRV can provide health-related information of cardio-vascular response to mental challenge. However, there is no association between sympatho-vagal balance at rest and classical cardiovascular risk factors.

Sex differences in drug addiction: a review of animal and human studies

Addiction research has historically neglected research on women, and most studies have been conducted on men only, with the concluding results generalized to the female population. The role of sex differences in vulnerability to drug abuse, their repercussions on prevention and treatment strategies all require detailed studies, as does the progression from recreational drug use to dependence. This review synthesizes evidence of gender differences in drug addiction, with particular emphasis on women's health and implications. We first reviewed behavioral studies showing sex differences in the preference for and self-administration of licit (i.e., alcohol and nicotine) and illicit (i.e., cocaine, amphetamine, heroin and cannabis) substances as revealed by animal models of addiction. Clinical studies demonstrating differences between men and women in craving, drug use, abstinence and relapse will then be examined. For both animal and human studies, the effects of hormones and estrous/menstrual cycle will be reviewed. Finally, neurobiological factors underlying gender differences in vulnerability to drug addiction (i.e., brain morphology and neurotransmission) and need for gender-specific detoxification treatments will be discussed.