Arterial stiffness describes how much the large arteries give way when the heart pushes blood into them. One common way to put a number on it is the augmentation index, which captures how much of the peak pressure in each beat comes from the pressure wave bouncing back off the body rather than from the heart's own push. Stiffer arteries send that wave back sooner and harder.
Drawn from background physiology, not from this paper.
Nitrate supplementation and caffeine have each been reported to push various aspects of cardiovascular function in conflicting directions. The authors set out to test whether taking nitrate alongside caffeine would offset the cardiovascular strain that caffeine imposes.
Drawn from the paper's introduction.
Twenty four healthy participants, seventeen of them male and averaging 24 years, completed four trials in a randomised, double blind, placebo controlled crossover: nitrate rich beetroot powder at 400 mg nitrate and a nitrate depleted version at 92 mg, each taken with and without 6 mg of caffeine per kilogram of body mass. Brachial and central blood pressure and arterial stiffness were measured before and 2.5 hours after supplementation, with flow mediated dilation assessed afterwards.
Caffeine on its own raised both stiffness measures. Augmentation pressure rose by 3(2) mmHg against 1(3) mmHg on placebo and 0(3) mmHg on nitrate alone, and the augmentation index reached 10(9) percent against 4(11) percent on placebo and 1(11) percent on nitrate alone, with p values from less than 0.001 to 0.007.
The combination behaved like placebo. Nitrate taken with caffeine gave an augmentation pressure of 1(3) mmHg and an augmentation index of 3(10) percent, which did not differ from placebo or from nitrate alone at p 0.505 to 0.689.
Nothing else moved. Brachial blood pressure, central blood pressure and flow mediated dilation showed no differences against placebo at p 0.067 to 0.359, and plasma cyclic guanosine monophosphate did not differ between conditions at p 0.370. Plasma nitrite was higher in both nitrate conditions than in placebo and caffeine at p less than 0.001, confirming the supplement was absorbed.
| Augmentation pressure, caffeine alone | +3(2) mmHg vs +1(3) placebo and +0(3) nitrate alone, p<0.001 to 0.007 |
| Augmentation index, caffeine alone | 10(9)% vs +4(11)% placebo and +1(11)% nitrate alone |
| Nitrate plus caffeine | augmentation pressure +1(3) mmHg, index +3(10)%, p=0.505 to 0.689 vs placebo and nitrate alone |
| Doses | 6 mg/kg caffeine; 400 mg nitrate vs 92 mg nitrate depleted |
| Brachial BP, central BP, flow mediated dilation | no differences vs placebo, p=0.067 to 0.359 |
| Plasma cyclic guanosine monophosphate | no difference between conditions, p=0.370 |
| Plasma nitrite | higher in both nitrate conditions, p<0.001 |
Not available The full discussion is not openly available and the abstract offers no mechanism, so we do not know what the authors think caused this.
Drawn from no open full text was reachable.
Two things endurance athletes commonly take on the same morning were shown to interact, with the nitrate drink holding one measure of arterial load at placebo levels when caffeine on its own raised it.
Healthy adults in their twenties, at rest, in a single session.
Nothing about training or racing yet. It moves the question from whether caffeine has a vascular cost to whether that cost matters over a season and whether anything at all changes downstream.
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