Caffeine in Food and Dietary Supplements Examining Safety: Workshop Summary (2014) / Chapter Skim
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5 Caffeine Effects on the Cardiovascular System
5 Caffeine Effects on the Cardiovascular System
Pages 67-88
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From page 67... ...
Higgins, M.D., M.B.A., University of Texas Medical School Endothelial cell function (ECF) serves an important role in mediating the vascular effects of caffeine exposure, according to John Higgins.
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From page 68... ...
He concluded that although some data indicate dose-dependent effects on some cardiac parameters, including heart rate and blood pressure, prevailing evidence suggests no effect on arrhythmia. In his opinion, clinical advice to limit caffeine consumption is based primarily on anecdote and folk lore, though some people may have individual sensitivity to caffeine.
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From page 69... ...
In the short term, during stress or certain exposures -- for example, in cold temperatures or during exposure to cigarette smoke or cocaine -- abnormal ECF impairs the ability of arteries to dilate normally and potentially could result in a supply-demand imbalance, that is, with the heart beating harder and needing more blood flow while at the same time not being able to open up the arteries to improve blood flow. This supply-demand imbalance could in the short term lead to ischemia and possibly cardiac arrhythmia.
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From page 70... ...
. The second study involved 10 individuals, all males, with an average age of 27, all of whom consumed 300 mg of caffeine and were tested 60 minutes later using a strain-gauge plethysmograph to measure forearm blood flow.
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From page 71... ...
The second study involved 18 individuals, 11 of whom were male, with an average age of 27 years, all of whom received 200 mg of pure caffeine and were then tested 50 minutes later while bicycling. The researchers found that exercise-induced myocardial blood flow response decreased 22 percent after caffeine ingestion (p < 0.01)
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From page 72... ...
The researchers measured adenosine disphosphate– induced platelet aggregation and the reactive hyperemia index (i.e., how the artery is able to dilate) both before and 1 hour after the volunteers consumed a 250-ml can of sugar-free energy drink.
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From page 73... ...
In healthy individuals aged 21 to 71 years who consume 200 to 300 mg of caffeine and then perform aerobic exercise 1 hour later, indirect tests indicate reduced ECF as measured by reduced myocardial blood flow. Finally, in healthy individuals aged 20 to 47 years who consume energy drinks, indirect tests indicate reduced ECF at rest.
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From page 74... ...
The researchers measured the amount of energy required to induce ventricular fibrillation with shocks to the heart among both control dogs and dogs that had experienced myocardial infarctions. They found that having had a myocardial infarction reduced the ventricular fibrillation threshold.
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From page 75... ...
With coffee drinking, there was no difference between habitual versus nonhabitual coffee drinkers with respect to sympathetic nerve activity or caffeine levels. A striking finding, in Goldberger's opinion, was that decaf administered to nonhabitual users increased blood pressure and sympathetic nerve activity.
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From page 76... ...
The researchers found that patients with moderately heavier caffeine use in the days prior to atrial fibrillation compared to usual intake had the lowest rate of successful spontaneous conversion to sinus rhythm. Patients with the lowest and highest intakes prior to atrial fibrillation had higher rates.
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From page 77... ...
According to Goldberger, the preponderance of these studies showed no increased risk of arrhythmias as a result of caffeine consumption. The largest of these population studies, Klatsky et al.
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From page 78... ...
In Goldberger's opinion, some data today suggest that caffeine effects are present, but the prevailing evidence shows no increase in arrhythmia. Moreover, what effects do exist are dose dependent and different in habitual versus nonhabitual users.
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From page 79... ...
However, it is important to note, El-Sohemy said, that a distinction exists between caffeine from energy drinks and caffeine from coffee. Caffeine is caffeine from a chemical structure perspective, but there is a big difference in terms of peak concentrations of caffeine between slowly sipping a hot beverage versus chugging a cold beverage.
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From page 80... ...
(2006) , El-Sohemy and colleagues examined genetic variation in CYP1A2 and coffee intake in more than two thousand cases of a first acute myocardial infarction and an equal number of controls matched for age, sex, and area of residence.
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From page 81... ...
, with slow metabolizers showing a more pronounced risk of heart attack, almost a fourfold increased risk, and with a significant protective effect of moderate consumption among fast metabolizers. El-Sohemy suspects that, at moderate levels of consumption, fast metabolizers are able to efficiently eliminate the caffeine, which would otherwise be masking some of the beneficial effects of the polyphenols and other bioactive substances.
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From page 82... ...
0 AA AC + CC * P<0.05 CYP1A2 Genotype FIGURE 5-1 Odds ratios of risk of myocardial infarction with coffee intake.
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From page 83... ...
(2011) reported that COMT could also explain why some people experience increased heart rate following caffeine consumption.
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From page 84... ...
PANELIST DISCUSSION WITH THE AUDIENCE Following El-Sohemy's presentation, workshop participants were invited to ask questions of the three panelists. Most of the discussion revolved around the future research needs on the cardiovascular effects of caffeine exposure, including in vulnerable populations, and differences between caffeine in energy drinks versus coffee.
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From page 85... ...
He did not disagree with the audience member's claim about other studies on performance, but he has been looking only at arterial function. Differences Between Caffeine in Energy Drinks Versus Coffee One audience member disputed El-Sohemy's claim that peak concentrations from chugging a cold drink are different from those from slowly sipping a hot beverage.
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From page 86... ...
2002. Coffee acutely increases sym pathetic nerve activity and blood pressure independently of caffeine con tent: Role of habitual versus nonhabitual drinking.
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From page 87... ...
2013. Caffeine reduces myocardial blood flow during exercise.
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From page 88... ...
2010. Detrimental effects of energy drink consumption on platelet and endothelial function.
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