Qual o papel do sódio na hidratação?

What is the role of sodium in hydration?

What is the role of sodium in hydration?

This may be the hottest week of the year here in São Paulo and it “seems” that just drinking water is no use…In fact, hydration is more than just drinking water. It involves a balance of electrolytes, and among them, sodium emerges as a key piece in this complex physiological puzzle. While many associate sodium with controlling blood pressure or seasoning food, its impact on the body's water regulation is underestimated. From maintaining osmotic balance to its vital function in thirst, sodium plays an important role in several processes that ensure our bodies remain properly hydrated. Let's find out how?


After exercise, fluid balance can be restored relatively quickly - this depends mainly on the degree of dehydration, time until the next workout or performance (if it is less than 8 hours, a more aggressive fluid consumption strategy may be necessary). ) and whether fluids are tolerated.

Ingesting the exact amount of fluid lost during exercise in the 2-4 hours after exercise will result in only a 50-70% restoration of fluid balance. This is partially because drinking fluids will result in an expansion of plasma volume, and this will trigger a series of responses that result in an increase in urine production. Therefore, to restore fluid balance in a short period of time, the athlete needs to drink more fluid than the fluids lost (150%). This additional volume compensates for the diuresis stimulated by the rapid consumption of large volumes of fluid. In other words, if you lose 1L of sweat, consume 1.5L of fluids.


The addition of sodium to isotonic drinks (liquids, powders or tablets) will stimulate more complete rehydration after the athlete becomes overhydrated due to exercise. Sodium will help restore plasma volume and fluid balance throughout the body compared to normal water intake. This sodium intake will increase blood sodium concentration and osmolality, which in turn stimulates renal water reabsorption. It is worth mentioning that urine production is inversely related to the sodium content in ingested liquids, therefore higher sodium concentrations are equivalent to lower urine production. It is important to note that sodium is a single important electrolyte in this case. Potassium may have a role to play in fluid distribution within the body, but sodium is the main driver of hydration.


Easy cola so you don't forget: the volume of liquid consumed is essential for rehydration after exercise and sodium helps retain this liquid. These are probably the two most important factors that determine rehydration after exercise.


“Gabi, can I drink coconut water to hydrate?” It's true that coconut water contains carbohydrates and electrolytes. However, coconut water contains little sodium, and that, as we just discussed, is the electrolyte that matters. It should also be noted that coconut water varies tremendously in composition depending on many factors, including the maturation process. Claims that coconut water is a superior source of hydration are unfounded, but it is a natural way to drink fluids that also contain carbohydrates and electrolytes.


Finally, how much sodium do we need? It depends! The amount of sodium we lose depends on the sweat rate, duration of exercise and the concentration of sodium in sweat. If any of these are very low, the total losses will likely be very low. Only if a “salty sweater” exercises long enough will the losses accumulate into something significant. In a study published in 2019, the average sodium concentration in sweat was 36.1 mmol/L or 0.8 grams per liter. There was substantial variation, with some losing as little as 0.25 grams per liter/L and others up to 2 grams per liter.


Although sweat sodium losses during exercise vary significantly from person to person and from day to day due to a number of factors, the ultimate need to replace sodium during exercise is to balance fluid intake and fluid losses and maintain a adequate osmolality, rather than preventing an actual sodium deficit.


Let's remember that the summer heat in Brazil is a little “atypical” and that maintaining adequate hydration is essential!


Thanks for reading and see you in the next post :)


Gabi

References:

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Maughan RJ, Leiper JB. Sodium intake and post-exercise rehydration in man. Eur J Appl Physiol Occup Physiol. 1995;71(4):311-9. doi: 10.1007/BF00240410. PMID: 8549573.

Maughan RJ, Owen JH, Shirreffs SM, Leiper JB. Post-exercise rehydration in man: effects of electrolyte addition to ingested fluids. Eur J Appl Physiol Occup Physiol. 1994;69(3):209-15. doi: 10.1007/BF01094790. PMID: 8001531.

Shirreffs SM, Aragon-Vargas LF, Keil M, Love TD, Phillips S. Rehydration after exercise in the heat: a comparison of 4 commonly used drinks. Int J Sport Nutr Exerc Metab. 2007 Jun;17(3):244-58. doi: 10.1123/ijsnem.17.3.244. PMID: 17693686.

Jeukendrup and Gleeson. Sport Nutrition. Human Kinetics Champaign IL 2018

Barnes KA, Anderson ML, Stofan JR, Dalrymple KJ, Reimel AJ, Roberts TJ, Randell RK, Ungaro CT, Baker LB. Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: An update and analysis by sport. J Sports Sci. 2019 Oct;37(20):2356-2366.

Lau WY. et al. Water intake after dehydration makes muscles more susceptible to cramp but electrolytes reverse that effect. BMJ Open Sport Exercise Med. 2019; 5(1):e000478