Sodium + Potassium
Overview:
Electrolytes are key to help our body function through daily life, but even more importantly, through exercise. Sodium and potassium can sufficiently be consumed from a dietary intake, with much of our sodium coming from a rich source, table salt, aka sodium chloride. Potassium can be gained from consuming enough fruits and vegetables, such as bananas, cantaloupes, and leafy greens. Sodium and water are lost through sweat which can require extra consumption for athletes, while potassium is lost at a rather consistent rate through fecal and renal exits.
Simple:
Sodium, potassium, and water work in conjunction together. Specifically sodium and water are lost due to sweat at a high rate with sodium loss being about 2-5% of the fluid loss from sweat in the body. This results in the need to rehydrate, with recommendations being about 230-690 mg/L of fluid for absorption before exercise to offset losses. It is important that an individual does not over hydrate with just water, because this can have the opposite effect if blood sodium concentrations are low, and will dehydrate further. Sodium and potassium are important to each other because they are what cause muscles to fire correctly and efficiently. The recommendation of potassium per day is 1600-2000 mg, and keeping these plasma levels high has positive effects on performance and muscle contractility, with low levels causing impaired exercise performance.
Complex:
Fluids and electrolytes prove to be an interesting topic of discussion when it comes to exercise and sports. It's important to understand the reason behind needing these in conjunction with each other. While the body is put into endurance training, or any exercise that requires the body to cool itself down, it begins to lose fluid and electrolytes, with sodium being the largest electrolyte loss. Many athletes may only consume water at a high amount which can actually dehydrate the body, instead of rehydrating.
Average sweat rates include 0.3 to 2.4 L/h depending on the person with sodium content as 50 mmol.L. Given this is is recommended that individuals drink sports drinks containing sodium from 230-690 mg/L for optimal absorption and also to prevent hyponatremia (low sodium in the blood) [1].
A common misconception regarding sodium and/or potassium is also that they can reduce cramps, and after reviewing many studies, that is not the case. Although both are required for rehydrating, the literature fails to protect that accusation [1].
A common replacement for sodium is table salt, or sodium chloride. High sweat rates result in the need for this replacement, but replacing with just water, especially high amounts of it, can lead to incomplete hydration, but also decreased performance, and heat cramps. While replacement during and after exercise is important, meeting higher dietary needs of something like table salt can negate some of the increased need for these replacements. Using table salt on foods, in water, and in sports drinks are an easy way to hit these needs, which equate to around 1.5g/day [2].
Fluid recommendations before exercise are important to offset dehydration during exercise. To be adequately hydrated, it is important to drink 400 mL to 600 mL of fluid around 2 hours before beginning your exercise, as well as drinking during exercise (150-300 mL) every 15 to 20 minutes. Keep in mind these values depend on things like body weight and individual physiology. Dehydration comes from exceeding body weight losses of more than 2% of body weight to put it into perspective [3].
In terms of potassium, which is lost at a very small amount through sweat, there is still a significant loss of potassium through fecal loss (400mg), and renal loss (200-400 mg). Thus, the recommendation for non-exercised individuals is 1600-2000 mg/day, which is also the same for exercised individuals as the losses due to sweat and heat are negligible [4]. This is where many sports drinks and rehydration drinks go wrong. Potassium and sodium and water are not the same, and increased sodium intake can change based on sweat and heat and exercise, while potassium intake will not change bodyweight from losses besides the ways previously mentioned. When you see drinks claiming “rehydration,” and are mainly potassium, with little sodium, they likely are targeting individuals who believe these two electrolytes are the same, and will not replenish fluid and sodium loss adequately.
An important study also showcases the importance for adequate potassium levels during muscular effort. “Muscle and plasma K+ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance” (Lindinger 1). The study then describes that elevations in plasma K+ have beneficial effects on a multitude of different physiological systems in the body, and a reduction can have implications on muscle and whole body fatigue, and impaired performance [5].
Works Cited:
- Veniamakis E, Kaplanis G, Voulgaris P, Nikolaidis PT. Effects of Sodium Intake on Health and Performance in Endurance and Ultra-Endurance Sports. Int J Environ Res Public Health. 2022 Mar 19;19(6):3651. doi: 10.3390/ijerph19063651. PMID: 35329337; PMCID: PMC8955583.
- Valentine V. The importance of salt in the athlete's diet. Curr Sports Med Rep. 2007 Jul;6(4):237-40. PMID: 17617999.
- Latzka WA, Montain SJ. Water and electrolyte requirements for exercise. Clin Sports Med. 1999 Jul;18(3):513-24. doi: 10.1016/s0278-5919(05)70165-4. PMID: 10410838.
- National Research Council (US) Subcommittee on the Tenth Edition of the Recommended Dietary Allowances. Recommended Dietary Allowances: 10th Edition. Washington (DC): National Academies Press (US); 1989. 11, Water and Electrolytes. Available from: https://www.ncbi.nlm.nih.gov/books/NBK234935/
- Lindinger MI, Cairns SP. Regulation of muscle potassium: exercise performance, fatigue and health implications. Eur J Appl Physiol. 2021 Mar;121(3):721-748. doi: 10.1007/s00421-020-04546-8. Epub 2021 Jan 4. PMID: 33392745.