What causes headaches in a young adult only when running, which improve with electrolyte intake?

Exercise-Induced Exertional Headache with Dehydration

This 24-year-old is experiencing exertional headaches during running caused by dehydration and electrolyte depletion, which responds appropriately to electrolyte replacement—the key management is ensuring adequate hydration with sodium-containing fluids before, during, and after running.

Primary Mechanism and Diagnosis

The throbbing headache occurring exclusively with running and improving with electrolyte intake strongly suggests exercise-associated dehydration with sodium depletion as the underlying cause 1. The throbbing quality is consistent with vascular changes that occur during dehydration, where reduced plasma volume leads to decreased cerebral perfusion and compensatory vasodilation 1.

Key diagnostic features to confirm:

• Headache timing: Occurs during or immediately after running, not at rest 1
• Response to treatment: Rapid improvement with electrolyte-containing fluids confirms the diagnosis 1
• Absence of other symptoms: No visual changes, focal neurological deficits, or fever that would suggest alternative diagnoses

Hydration Strategy to Prevent Headaches

Pre-Exercise Hydration

Start exercise in a euhydrated state by drinking 6 mL of fluid per kg of body weight every 2-3 hours before running 1. For a 70 kg individual, this equals approximately 420 mL every 2-3 hours.

Euhydration indicators 1:

• Daily body mass changes <1%
• First morning urine specific gravity <1.020
• Plasma osmolality <290 mmol/kg

During Exercise Hydration

For runs lasting longer than 1 hour, consume fluids containing 0.5-0.7 g/L of sodium 1. This sodium concentration is critical because:

• Sweat rates during vigorous exercise commonly reach 1.0-1.5 L/hour, with some individuals exceeding 2.5 L/hour 1
• Sodium is the main electrolyte lost in sweat, and inadequate replacement can trigger symptoms including headaches 1
• Athletes training in heat have higher daily sodium requirements than the general population 1

Add 30-60 g/hour of carbohydrates to the hydration regimen for exercise lasting longer than 1 hour 1. This can be achieved through sports drinks or a combination of fluids and solid foods 1.

Fluid Volume Guidelines

Minimize body water mass losses without increasing body weight during exercise 1. More specifically:

• Athletes should not lose greater than 2-3% of body weight during runs lasting longer than 1.5 hours 1
• Dehydration exceeding 2% of body mass impairs aerobic performance and exacerbates physiological strain in warm-hot environments 1

Practical Implementation

Immediate Management

For this specific patient experiencing headaches:

1. Measure baseline body weight (post-void, nude, in the morning on consecutive days after consuming 1-2 L of fluid the prior evening) 1
2. Weigh before and after typical runs to calculate individual sweat rate 1
3. Consume a solution with 0.5-0.7 g/L sodium during runs, increasing to 1.5 g/L if symptoms persist 1

Beverage Selection

Hypertonic water with added carbohydrates and sodium improves water absorption efficiency 1. Commercial sports drinks typically provide appropriate sodium and carbohydrate concentrations, though some athletes may need additional sodium supplementation 1.

Important Caveats

Avoid Overhydration

While dehydration causes this patient's headaches, excessive fluid consumption can lead to exercise-associated hyponatremia (EAH), a potentially fatal condition 2. Risk factors include:

• Racing time above 4 hours 2
• Substantial weight gain during exercise 2
• Female sex and low body mass index 1

The goal is euhydration, not hyperhydration—athletes should minimize body water losses without gaining weight 1.

"Drinking to Thirst" Limitations

While some advocate drinking to thirst 1, this approach often results in body water deficits exceeding 2-3% of body mass when sweat rates are high 1. For this patient with symptomatic dehydration, a more structured hydration plan is necessary 1.

Post-Exercise Recovery

Following runs, consume fluids and electrolytes to offset 100-150% of body mass losses if aggressive rehydration is needed 1. This accounts for ongoing urine losses during the recovery period 1.

Red Flags Requiring Further Evaluation

Seek additional medical evaluation if:

• Headaches persist despite adequate hydration and electrolyte replacement
• New symptoms develop (visual changes, neck stiffness, focal weakness)
• Headaches occur at rest or with activities other than running
• Progressive worsening despite intervention

The improvement with electrolyte intake strongly supports a benign, preventable cause, but persistent symptoms warrant investigation for alternative etiologies including exertional migraine or cardiac causes 1.