How to hydrate correctly for exercise, recovery and health (part 2)
In part one of this two-part series on hydration, we explored the critical role hydration plays in health and performance and how our sophisticated thirst mechanism works. We also discussed how our bodies naturally regulate fluid and electrolyte needs, and why rigid hydration rules may be counterproductive.
With this background of understanding, our goal is to explain that definitions of dehydration can vary, and how (generally) we can rely on our body’s physiology to regulate fluid intake, rather than having a rigid drinking plan.
In this follow up article, we’ll dive deeper into the nuances of hydration, focusing on dehydration definitions, overhydration issues in sport, hydration strategies for athletes, and the effects of caffeine and alcohol on hydration.
We’ll also provide some guidelines around water intake to give a clear indication of normal ranges.
A quick recap on part 1
Hydration is essential for regulating body temperature, supporting cognitive and physical performance, and maintaining cellular function.
While rough hydration guidelines exist, individual needs vary, and our body’s sophisticated thirst mechanism is a reliable gauge.
Dehydration and overhydration both present risks, and striking the right balance is key to optimising health and athletic performance.
The various definitions of dehydration
Dehydration is often broadly understood as insufficient water levels in the body, with mild dehydration defined as a loss of 2% of body weight from fluid loss.
But dehydration can be categorised more specifically as:
Isotonic dehydration: equal loss of water and electrolytes, typically seen in conditions like diarrhea or vomiting.
Hypertonic dehydration: greater water loss relative to electrolytes, often caused by excessive sweating or inadequate water intake.
Hypotonic dehydration: greater electrolyte loss relative to water, which can result from overhydration without adequate electrolyte replacement.
Each type of dehydration has unique physiological effects and recognising the differences is essential for appropriate treatment.
The issue of overhydration in sport
While dehydration often gets more attention, overhydration (or excessive fluid intake), can dilute blood sodium levels, leading to a dangerous condition known as hyponatremia.
Exercise-associated hyponatremia (EAH) is a growing concern in endurance sports like marathons and triathlons.
This condition arises when endurance athletes drink more fluid than their kidneys can excrete.
According to Rosner (2019) two major pathologic mechanisms largely account for the development of EAH: excessive fluid intake and impaired urinary water excretion, which is largely a result of persistent secretion of arginine vasopressin (AVP), also referred to as antidiuretic hormone or ADH.
How to hydrate appropriately for sport
Because fluid loss through sweat and urine are dynamic and variable across individuals and sports, fixed ranges of fluid intake are not appropriate.
Hydration strategies for sport must account for the type, intensity and duration of activity, as well as an individual’s unique needs.
The first line approach is to listen to your thirst - though endurance athletes can use additional tools such as monitoring body weight (i.e. weight gain during an endurance event would mean that fluid intake should be reduced).
Below are some helpful tips on hydrating appropriately during sport or exercise:
Listen to thirst: for activities under 60 - 90 minutes, drinking when thirsty is usually sufficient.
Plan for extended sessions: in prolonged or high-intensity exercise, aim to consume 400 to 800 mL per hour . Monitoring pre and post-exercise body weight can help estimate sweat losses.
Electrolyte replenishment: for endurance events, include sodium and potassium in your hydration plan to avoid imbalances.
The role of sports drinks
Electrolyte drinks (such as sports drinks) help replenish sodium, potassium and other electrolytes lost through sweat and deliver carbohydrates, helping to replenish glycogen stores.
A typical sports drink provides about 6 - 9% carbohydrate concentration, which has been shown to sustain blood glucose levels during exercise and improve endurance by delaying glycogen depletion.
The benefits of electrolyte drinks:
Maintain electrolyte balance, reducing the risk of cramping.
Improve water absorption.
Provide carbohydrates for energy during endurance activities.
The disadvantages of electrolyte drinks:
High sugar content in some products may lead to unnecessary calorie intake.
Overuse can result in excessive sodium consumption for young individuals or those with a sedentary lifestyle.
For shorter workouts, plain water is often sufficient. Athletes should match fluid and electrolyte intake to the intensity and duration of their activity.
Caffeine, alcohol and other diuretics and their impact on hydration
The long-held belief that caffeine dehydrates you is a misconception. While caffeine is a mild diuretic, research shows that moderate consumption does not lead to dehydration.
The fluid content in caffeinated beverages contributes to hydration, and the diuretic effect of caffeine is minimal. The result? A net increase in fluid levels for most individuals.
Diuretics, including caffeine and certain medications, increase urine production by influencing kidney function. However, the extent of fluid loss depends on the specific diuretic and the individual’s overall fluid balance. In moderate doses, diuretics like caffeine have negligible effects on hydration status.
Unlike caffeine, alcohol has a more pronounced diuretic effect, inhibiting the release of antidiuretic hormone (ADH). This leads to increased urine production and a higher risk of dehydration, particularly when consumed in large quantities.
Guidelines for daily hydration
While daily fluid needs vary, here are some general guidelines for informational purposes:
Men: 3.7 litres of total fluid (including water, beverages and food).
Women: 2.7 litres of total fluid (including water, beverages and food).
Remember, these are only rough estimates, and your thirst mechanism remains a reliable guide for most daily hydration needs.
Key takeaways
Hydration is personal. Guidelines offer rough estimates but your thirst mechanism is a reliable indicator when it comes to your daily hydration - and for sport and exercise (although other tools may be implemented in extended exercise situations).
Overhydration is a real issue, particularly for endurance athletes. Avoid excessive water intake during exercise, particularly without electrolytes.
Sports drinks are multifunctional but use them wisely for prolonged or intense activity to replenish fluids and carbohydrates.
Moderate caffeine intake will not dehydrate you, but alcohol has a more significant diuretic effect that requires proactive hydration.
By understanding your body’s needs and respecting its thirst signals, you can achieve the right balance to optimise performance and health.
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