The Role of Sodium in Sports Hydration

Sodium is the primary electrolyte lost in sweat.



It plays several critical roles:

  • Maintains blood plasma volume

  • Supports nerve signaling and muscle contraction

  • Improves fluid absorption in the small intestine

  • Helps prevent excessive dilution of blood sodium levels



Recommended sodium concentrations in sports drinks = 460–1150 mg sodium per liter


Athletes who sweat heavily or compete in hot conditions often require sodium at the upper end of this range.




Potassium and Electrolyte Balance

Potassium is also lost in sweat, though at lower levels than sodium.



Typical recommended concentrations =  80–200 mg potassium per liter



Potassium helps maintain electrical gradients across muscle and nerve cells.

Maintaining a balanced sodium-to-potassium ratio also supports cardiovascular health.



Research suggests:

  • Na:K ratio under-1 is ideal for cardiovascular health (chemistry reminder that's sodium:potassium ;)

  • • Ratios over-2 may be sub-optimal






Carbohydrates in Sports Drinks: When They Matter

Electrolytes alone support hydration, but carbohydrates become important during longer or high-intensity sessions.



Recommended carbohydrate concentration:

• 6–8% carbohydrate solution



This equals:

• 60–80 g carbohydrate per liter of fluid



Why this range works:

  • Enhances fluid absorption in the gut

  • Supports glucose delivery to working muscles

  • Maintains blood glucose during prolonged exercise



However, too much sugar without adequate water can cause problems.



Potential consequences:

  • Gross taste in your mouth

  • Nausea

  • Digestive upset

  • Cramping

  • Poor absorption of nutrients




Sports Gels and Hydration

Sports gels provide carbohydrate and electrolytes but contain little water.

That means water intake becomes even more important.



Best practice:

• Always consume water with sports gels

Without adequate fluid, gels can slow gastric emptying and cause gastrointestinal distress.





Electrolyte Formulas: What Athletes Should Know



Most electrolyte formulas are well tolerated.



Possible side effects include:

  • Fluorescent yellow urine

  • Bloating

  • Nausea

  • Headaches

  • Diarrhea or constipation




These symptoms often occur when:

  • Electrolytes are overly concentrated

  • Water intake is insufficient

  • Products contain artificial colors or additives



Reading labels matters.




Hydrating in Rhythm with a Menstrual Cycle

In the Late luteal (10d prior to menses) progesterone and estrogen are both high. This has many effects on our hydration and and water needs.



In the luteal phase body temperature goes up due to progesterone. This combined with elevated estrogen in this phase, has some very real affects on the rest of the body:


  • urinary output goes down - renin-angiotensionigen system is activated from estrogen

  • sweat output goes up (1)

  • threshold temperature to sweat increases



Add to this, the thirst sensation is dulled OR MAYBE increased. The current scientific evidence is mixed on this subject. So you need to pay attention to your own unique rhythms.



As a result, plasma volume in the blood drops by about 8% making the blood thicker and harder to move. The heart has to pump harder and faster to keep the blood moving and oxygen to our brain, muscles and every cell of the body. You may have noticed that your resting heart rate in the luteal phase is about 2-3bpm faster than in the follicular phase.



To stay properly hydrated throughout our cycle, we need to be aware of the cycle, how it affects our hydration and make a hydration plan for both follicular and luteal phases





The Bottom Line for Athletes

Hydration is a physiological performance system, not just a habit.




A simple framework:


Daily

• 1.5–3 L fluid depending on training



Before training

• ~500 mL water 1–2 hours before exercise


During training

• 150–350 mL every 15–20 minutes


Long sessions (>1 hour)

• Add electrolytes

• Consider carbohydrates (6–8%)


**Consider adding more fluids in your luteal phase



Athletes often focus heavily on training intensity.




But performance frequently comes down to how well the body moves water, electrolytes, and glucose through muscle and nerve tissue during stress.




Hydrate like an athlete… because your physiology depends on it.





References

https://europepmc.org/article/MED/25230913


Aguree S, Bethancourt H, Taylor LA, Rosinger AY, Gernand AD. Plasma volume variation across the menstrual cycle among healthy women of reproductive age: A prospective cohort study. Physiol Rep. 2020; 8:e14418. https://doi.org/10.14814/phy2.14418