Acute dietary nitrate supplementation improves dry static apnea performance
Authors: Harald K. Engan, Andrew M. Jones, Fanny Ehrenberg, Erika Schagatay
DOI / Source: 10.1016/j.resp.2012.05.007
Date: 07 May 2012
Reading level: Beginner
Why This Matters for Freedivers
This is one of the rare supplement studies that tests freedivers directly and finds a clear performance effect: a single dose of beetroot/nitrate increased maximal dry static time by about 11%. It also suggests nitrate may reduce “oxygen burn rate” early in the hold (less desaturation in fixed-time apneas), which is exactly what we’re trying to achieve with relaxation and an efficient dive response.
Synopsis
Beetroot juice (and dietary nitrate in general) is famous in endurance sports because it can lower blood pressure and reduce the oxygen cost of exercise. This paper asks a simple freediving question: if nitrate can make the body more “oxygen-efficient,” could it help you hold your breath longer—especially in a still, dry static where the main limiter is how fast you use up your oxygen stores?
The researchers tested this in 12 trained apnea divers (9 men, 3 women) using a randomized, double-blind crossover design. On one day the divers drank 70 ml of concentrated beetroot juice containing about 5 mmol of nitrate. On another day they drank a placebo juice with almost no nitrate. The drinks were taken 2.5 hours before testing (when nitrate effects are usually strongest).
Each test day followed the same routine: after resting, the divers did two controlled 2-minute statics (sub-maximal, same duration for everyone) separated by short recovery, then a final maximal-effort static. Heart rate and oxygen saturation were measured continuously, and resting blood pressure was measured before the apneas.
The key result: beetroot/nitrate increased maximal apnea duration by about 11% (roughly 28 seconds longer on average). That’s a meaningful change for a single acute intervention. During the fixed 2-minute statics, oxygen saturation dropped less after beetroot than after placebo, even though the apnea time was identical—suggesting the body may have used oxygen more slowly during those holds. Resting mean arterial pressure was also slightly lower after beetroot.
Interestingly, the classic diving bradycardia during the short sub-max apneas wasn’t clearly different between conditions, which hints that the benefit wasn’t simply “a stronger dive response.” Instead, the authors suggest the main driver could be reduced metabolic cost (your tissues doing the same thing while spending less oxygen). In the maximal apneas, oxygen saturation ended lower after beetroot—but that likely reflects the fact that the divers stayed down longer, allowing saturation to fall further before they stopped.
The overall takeaway is practical: in trained divers, acute dietary nitrate (via beetroot juice) can measurably extend dry static performance, and the pattern of oxygen saturation changes fits the idea of improved efficiency or reduced oxygen consumption—at least during shorter, controlled holds.
Abstract
Acute dietary nitrate (NO3−) supplementation has been reported to lower resting blood pressure, reduce the oxygen (O2) cost of sub-maximal exercise, and improve exercise tolerance. Given the proposed effects of NO3− on tissue oxygenation and metabolic rate, it is possible that NO3− supplementation might enhance the duration of resting apnea. We investigated the effects of acute NO3− supplementation on pre-apnea blood pressure, apneic duration, and the heart rate (HR) and arterial O2 saturation (SaO2) responses to sub-maximal and maximal apneas in twelve well-trained apnea divers. Subjects were assigned in a randomized, double blind, crossover design to receive 70 ml of beetroot juice (BR; containing ∼5.0 mmol of nitrate) and placebo juice (PL; ∼0.003 mmol of nitrate) treatments. At 2.5 h post-ingestion, the subjects completed two 2-min static apneas followed by a maximal effort apnea. Relative to PL, BR reduced resting mean arterial pressure by 2% and increased maximal apneic duration by 11% (PL: 250 ± 58 vs. BR: 278 ± 64 s). The mean nadir for SaO2 after the two sub-maximal apneas was higher after BR than PL, while in the longer maximal apneas in BR the magnitude of the reductions in HR and SaO2 were greater than in PL. The results suggest that acute dietary NO3− supplementation may increase apneic duration by reducing metabolic costs.