Dietary nitrate enhances arterial oxygen saturation after dynamic apnea
Authors: Alexander Patrician, Erika Schagatay
DOI / Source: 10.1111/sms.12684
Date: 01 March 2016
Reading level: Beginner
Why This Matters for Freedivers
In dynamic apnea, you’re spending oxygen while you’re moving, so the “oxygen budget” runs out fast. This study suggests beetroot/nitrate can leave you with a slightly bigger safety buffer after a 75 m swim—higher oxygen saturation after surfacing—which could translate to better margins and potentially better performance when you’re doing repeated dives or training sets.
Synopsis
Freedivers train to make every dive “cheaper”: less oxygen spent for the same distance. Dietary nitrate (often taken as beetroot juice) is known to reduce the oxygen cost of exercise in many sports, so this study asked a very freediving-specific question: does nitrate help you come up with more oxygen left in the tank after a dynamic apnea swim?
Fourteen experienced male apnea divers took part in a randomized, double-blind crossover test. On one day they drank 70 mL of nitrate-rich beetroot juice (about 5 mmol nitrate). On another day they drank a placebo beetroot drink with almost no nitrate. The drinks looked and tasted the same, and testing happened 2.5 hours later (when nitrate effects are expected to peak).
The task was simple and standardized: each diver performed two 75 m dynamic apneas with fins in a pool, with 4.5 minutes rest between swims. To keep things consistent, they were not allowed warm-up apneas, hyperventilation, or lung packing. Oxygen saturation (SaO2) and heart rate were measured for 90 seconds before and after each swim using finger pulse oximetry.
The main result: after the 75 m swims, oxygen saturation was better with beetroot juice. The average lowest saturation (the post-dive “nadir”) was about 83% with beetroot versus about 78% with placebo. At 20 seconds after surfacing—a key moment when many divers are still dropping—SaO2 was also higher with beetroot (mid-80s%) than placebo (high-70s%). Importantly, heart rate during recovery didn’t differ between conditions, which suggests the improved oxygen numbers weren’t simply due to a stronger bradycardia response.
So what’s the likely explanation. The most straightforward interpretation is that nitrate reduced the oxygen cost of the underwater work—meaning the divers used less oxygen during the swim, so they surfaced with more remaining. The study didn’t measure muscle oxygen use directly, but this pattern matches what nitrate does in other exercise contexts: making movement a bit more oxygen-efficient.
A practical nuance the authors discuss is measurement timing: finger oximetry lags behind what’s happening in the lungs by around 15–20 seconds, so the real “end-of-dive” low point appears slightly later on the sensor. That’s why the 20-second post-surface comparison is especially meaningful.
Bottom line: in trained divers doing a controlled 75 m dynamic apnea, beetroot/nitrate produced a small but clear improvement in post-dive oxygen saturation. That doesn’t guarantee a new PB, but it suggests a real oxygen-conserving effect that could improve safety margins and possibly help performance in maximal attempts or repeated training dives.
Abstract
Breath-hold divers train to minimize their oxygen consumption to improve their apneic performance. Dietary nitrate has been shown to reduce the oxygen cost in a variety of situations, and the aim of this study was to examine its effect on arterial oxygen saturation (SaO2) after dynamic apnea (DYN). Fourteen healthy male apnea divers received either 70 mL of concentrated nitrate-rich beetroot juice or placebo on different days. At 2.5 h after ingestion, they performed 2 × 75 m DYN dives in a pool with 4.5-min recovery between dives, without warm-up apneas, hyperventilation, or lung packing. SaO2 and heart rate were measured via pulse oximetry for 90 s before and after each dive. Mean SaO2 nadir values after the dives were higher with beetroot juice than placebo, and SaO2 was also higher 20 s post-dive. The results suggest an oxygen-conserving effect of dietary nitrate supplementation, likely improving safety margins in submaximal dives and potentially benefiting maximal apnea performance.