No More Head Spins: The Athlete’s Guide to Beating Faintness and Migraines

Staying hydrated and topping up key minerals, sodium, potassium, calcium, and magnesium, helps keep your blood pumping and your head clear during sport. Even losing just 2% of your body weight in sweat can impair endurance by up to 10% and cause dizziness, near-faints (presyncope), or full fainting (syncope), slowing you down and risking injury [1][2].

Replacing plain fluids without salts can lead to cramps, impaired nerve signalling, and reduced muscle function. However, avoiding dehydration is not simply a matter of drinking water, and as recent sports science highlights, it is certainly not a one-size-fits-all approach.

Why Women Heat Up Faster (And Why It Matters)

For decades, hydration advice was based almost entirely on male participants. But as thermoregulation expert Dr. Stacy Sims highlights in her article, Hydration is Power: Harness Yours, women are not small men.

We use the water in our bodies to get rid of the heat we produce while exercising. Blood circulates to the skin to dump heat through evaporative cooling. While we often hear the human body is about 60% water, in females, that number is closer to 50% due to a naturally higher percentage of fat tissue, which does not hold as much fluid as skeletal muscle.

Because women start with less total body water and lower blood volume, a 2% drop in weight from sweat represents a much larger portion of our total fluid reserves [15]. This leads to greater cardiovascular strain. Furthermore, because women generally sweat less than men, our core body temperature rises roughly twice as quickly when we start exercising.

Sex hormones also alter fluid compartmentalisation. During the luteal phase of the menstrual cycle, resting and exercising core body temperature increases by 0.3 to 0.5°C [15]. Crucially, high levels of oestrogen and progesterone can blunt the thirst mechanism, meaning your blood volume could be dropping without you actually feeling thirsty.

Dehydration as a Migraine and Fainting Trigger

When you factor in that faster core temperature rise and a blunted thirst mechanism, the mechanical risks become clear. When you sweat out water and electrolytes without replacing them properly, your blood volume shrinks. This reduces oxygen delivery to your brain and muscles, setting the stage for syncope [1][5].

Dehydration is also a common trigger for migraines, with about one-third of sufferers naming low fluid levels as a primary cause [3][4]. Even mild dehydration alters brain chemistry and increases neuronal excitability, triggering migraine pathways. Clinical studies show that restoring fluids promptly can ease dehydration-induced migraine symptoms within 30 minutes [4].

Hydration Options Compared

Plain Water

• Pros: Zero calories, sugar-free, and universally available. Sufficient for workouts under 60 minutes in moderate conditions [8].

• Cons: Does not replace sweat-lost electrolytes. High fluid intake without electrolytes can lead to increased urination and lowered blood sodium rather than cellular hydration, risking cramps and hyponatremia (dangerously low sodium) [9].

Dr. Stacy Sims’ DIY Hydration Mix

• Pros: To optimise fluid absorption, Dr. Sims recommends a targeted formula: 500 ml of water mixed with 1/16 tsp of sea or Himalayan salt (145–250 mg sodium) and 1 tsp of maple syrup or honey. This creates an ideal 1–3% carbohydrate concentration. The sugar activates the sodium-glucose transport in the gut, actively pulling fluid into the bloodstream.

• Cons: Requires precise measurement and preparation before training.

Commercial Sports Drinks

• Pros: Provide a convenient, ready-to-drink source of fluid and electrolytes [5][6].

• Cons: Most commercial sports drinks are too concentrated (6–8% carbohydrates), which actually hinders rapid fluid absorption in the gut. They are also often high in added sugars, calories, artificial colours, and flavours [7][10].

Coconut Water

• Pros: Naturally rich in potassium (~600 mg per 240 ml) and moderate in magnesium (15 mg per 240 ml), with natural sugars and no artificial additives [4].

• Cons: Contains lower sodium (~252 mg per 240 ml) than most sports drinks, which is insufficient for heavy sweaters unless a pinch of salt is added [13].

Electrolyte Powder Mixes

• Pros: Enable precise dosing for individual sweat rates.

• Cons: Require pre-mixing and planning, and can be more expensive per serving [12].

Practical Hydration Strategies

To preserve blood volume, replace lost electrolytes, and support optimal brain and muscle function, you need a strategy that matches your physiology and the environment.

1. Morning Pre-Load: Drink 300–500 ml of your chosen fluid (Dr. Sims’ DIY mix, salted coconut water, or an electrolyte powder) 30 to 60 minutes before activity [6]. This actively improves blood volume before your core temperature begins to rise.

2. Sip During Activity: Aim for 150–250 ml every 15–20 minutes. For sessions longer than 60 minutes or in the heat, alternate coconut water with a higher-sodium option, or add ½ tsp (≈1,000 mg) of salt to your coconut water [10].

3. Adjust for Female Physiology: As noted by Dr. Sims, instead of replacing strictly by body weight, use temperature guidelines:

   • 24°C and below: Aim for roughly 7.8 ml per kg of body weight per hour.

   • 27°C and above: Aim for roughly 10.4 ml per kg of body weight per hour.

4. Post-Exercise Rehydration: Weigh yourself before and after. For each kilogram lost, consume approximately 1.2 litres of fluid to fully restore balance [5].

5. Migraine Prevention: Properly rehydrating reduces migraine frequency, but daily magnesium supplementation (~400 mg) is also "probably effective" for migraine prophylaxis, trimming monthly migraine days by 1–2 [14]. Coconut water’s magnesium and potassium bolster this approach.

Whether you prefer a custom powder mix, Dr. Sims' DIY formula, or salted coconut water, the mechanical goal is the same. By tailoring your hydration choice to your workout intensity and understanding your specific physiological responses to heat, you can prevent dizziness, fainting, and dehydration-induced migraines—staying sharp and at your best from warm-up through cool-down.

References

1. The Dietitian Resource. Dehydration Effects on Sports Performance. https://thedietitianresource.com/dehydration-effects-on-sports-performance/

2. WebMD. Migraine and Dehydration: Is There a Link? https://www.webmd.com/migraines-headaches/migraine-dehydration-link

3. American Migraine Foundation. Top 10 Migraine Triggers and How to Deal with Them. https://americanmigrainefoundation.org/resource-library/top-10-migraine-triggers/

4. NutritionFacts.org. Water vs. Coconut Water vs. Sports Drinks for Athletes. https://nutritionfacts.org/blog/water-vs-coconut-water-vs-sports-drinks-for-athletes/

5. MedicineNet. Exercise-Associated Hyponatremia: Who’s at Risk? https://www.medicinenet.com/drinking_too_much_water_and_exercising_dangerous/views.htm

6. Cleveland Clinic. Are Electrolyte-Loaded Sports Drinks Healthy? https://health.clevelandclinic.org/electrolyte-drinks-beneficial-or-not

7. Boca Grande Health Clinic. Ask a Doc: The Pros and Cons of Electrolyte Beverages. https://www.bghc.org/news/healthcare/ask-a-doc-the-pros-and-cons-of-electrolyte-beverages/

8. Sports Dietitians Australia. Hydration: How Much Should You Drink During Exercise? https://www.sportsdietitians.com.au/sda-blog/hydration-during-exercise/

9. MedicineNet. Drinking Too Much Water and Exercising: Dangerous? https://www.medicinenet.com/drinking_too_much_water_and_exercising_dangerous/views.htm

10. TrainingPeaks. Hydrate Right: Military Hydration Guidelines. https://www.kennesaw.edu/employee-wellness/docs/acsm-hydration-for-fitness.pdf

11. EatingWell. We Asked 5 Dietitians the Best Electrolyte Supplement—They All Picked the Same One. https://www.eatingwell.com/dietitians-favorite-electrolyte-supplement-11736890

12. INEVIFIT. Electrolyte Powder vs. Sports Drinks: Which One Fuels Your Workout Better? https://inevifit.com/blogs/health-fitness/electrolyte-powder-vs-sports-drinks-which-one-fuels-your-workout-better-1

13. Precision Hydration. Why Drinking Coconut Water During Exercise Is Coco-Nuts. https://www.precisionhydration.com/performance-advice/hydration/why-drinking-coconut-water-is-coco-nuts/

14. Migräne und Kopfschmerz. Magnesium for Migraine Prophylaxis: A Meta-Analysis. https://www.migrainecanada.org/hydration-and-migraine/

15. Wickham, K. A., McCarthy, D. G., Spriet, L. L., & Cheung, S. S. (2021). Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms. Journal of Applied Physiology.