The Sport Science of Sodium and Hydration

Dr Dan Plews sits down with Dr Alan McCubbin - sports nutrition researcher and one of the most credible voices on sodium and hydration in endurance sport - to separate the science from the marketing. They cover what sodium actually does in the body, why fluid balance matters more than sodium dose alone, and where supplementation genuinely makes a difference.

10 key takeaways for athletes

1. Sodium's primary job is signalling to your brain whether to drink more, retain fluid, or excrete water - not hydrating you directly.
   
2. Changing your diet for three days shifts sweat sodium concentration by around 10 to 12 percent. Real but modest.
   
3. True sodium deficiency from sweat losses is extremely unlikely in modern diets. Most problems come from fluid imbalance not sodium depletion.
   
4. Your kidneys adapt fast. Athletes who lost 5,500mg of sodium over five hours cut their urinary sodium excretion by two thirds in the 24 hours after -- without supplementing.
   
5. The 1,000mg morning sodium trend is a hydration retention play. It works when drinking large volumes on an empty stomach. Once food is involved the effect largely disappears.
   
6. Pre-exercise hyperhydration is the clearest use case for sodium -- most relevant for hot, high intensity events where fluid access is limited during competition.
   
7. Sodium during exercise doesn't directly improve performance. If it helps you drink enough fluid to stay hydrated, performance may improve as a result.
   
8. Hyponatremia is a fluid problem not a sodium problem. Overdrinking is the risk. Sodium cannot rescue clear overhydration.
   
9. Sweat sodium testing has limited value if your event is under four hours. General guidelines are enough for most athletes.
   
10. Sodium matters but context matters more. Event duration, heat, and drinking behaviour should drive your hydration strategy -- not chasing a specific number every session.
    

00:00 - Why Dan wanted Alan on to talk sodium
03:34 - The old research on diet and sweat sodium
09:10 - What sodium actually does in the body
11:32 - How sodium drives thirst and kidney responses
22:16 - Five hours of heat running and kidney adaptation
26:32 - The rise of the 1,000 milligram morning sodium trend
36:44 - Pre-loading fluid for hot, long events
47:04 - During-exercise sodium and the real mechanism
49:24 - What hyponatremia actually does in the body
60:21 - Why recovery and post-exercise hydration is where sodium helps most
64:25 - Whether sweat sodium testing is worth it for most athletes
69:21 - Where Pillar's 400 milligram hydration product fits

Connect:

Dr Alan McCubbin: https://www.instagram.com/fuelingendurance/

Dr. Dan Plews: instagram.com/theplews

Shop: pillarperformance.shop

Instagram: instagram.com/pillarperformance

Strava: strava.com/clubs/1108245