I experience dizziness after running 12 km, what could be causing it and how can I manage it?

Dizziness After Running 12 km: Causes and Management

Your post-run dizziness is most likely caused by dehydration with electrolyte depletion, and you should focus on proper hydration strategies before, during, and after your runs to prevent this symptom. 1

Primary Causes to Consider

Dehydration and Electrolyte Imbalance (Most Likely)

• Dehydration with sodium depletion is the most common cause of exercise-induced dizziness after prolonged running, particularly in distances like 12 km where fluid losses can be significant 1, 2
• Reduced plasma volume from dehydration leads to decreased cerebral perfusion and compensatory vasodilation, which manifests as dizziness 1
• This mechanism is distinct from true vertigo and represents a presyncope-type dizziness related to inadequate cerebral blood flow 3, 4

Exercise-Induced Physiological Changes

• During prolonged running, blood flow is redirected away from the splanchnic circulation (including the gut) to working muscles, which can contribute to systemic symptoms including dizziness 5
• The intensity-dependent reduction in mesenteric blood flow during exercise can affect overall cardiovascular stability 5

Heat-Related Illness

• Headache and dizziness are cardinal symptoms of heat exhaustion, especially when running in temperatures above 70°F (21°C) with high humidity 2
• Core temperature elevation combined with dehydration significantly increases the risk of these symptoms 2

Prevention Strategy: Hydration Protocol

Pre-Run Hydration

• Start your run in a euhydrated state by drinking 6 mL of fluid per kg of body weight every 2-3 hours before running 1
• Confirm adequate hydration by checking that your first morning urine specific gravity is less than 1.020 and daily body mass changes are less than 1% 1

During-Run Hydration (Critical for 12 km Distance)

• For runs lasting longer than 1 hour, consume fluids containing 0.5-0.7 g/L of sodium 1
• Add 30-60 g/hour of carbohydrates to your hydration regimen for runs exceeding 1 hour 1
• If symptoms persist despite this strategy, increase sodium concentration to 1.5 g/L 1

Post-Run Recovery

• Consume fluids and electrolytes to offset 100-150% of body mass losses if aggressive rehydration is needed 1
• Measure your baseline body weight and weigh before and after typical runs to calculate your individual sweat rate 1

Critical Warning: Avoid Overhydration

• Do not drink excessively, as this can lead to exercise-associated hyponatremia (EAH), a potentially fatal condition 6, 1
• EAH affects 3-22% of marathon runners and presents initially with dizziness, headache, nausea, and bloating before progressing to altered mental status 6, 2
• The goal is euhydration (balanced hydration), not hyperhydration—you should minimize body water losses without gaining weight 1

Additional Contributing Factors to Address

Nutritional Timing

• Avoid running within 2 hours of eating, as competing blood flow demands between digestion and exercise can contribute to dizziness 2
• In the days before long runs, avoid high-fiber foods that can delay gastric emptying 5

Medication Review

• Avoid NSAIDs (ibuprofen, aspirin) before and during running, as they increase gastrointestinal permeability and can exacerbate exercise-related symptoms including dizziness 5
• These medications should be particularly avoided if you have a history of gastrointestinal problems during exercise 5

Environmental Considerations

• Avoid exercising in extreme heat and humidity when possible 2
• High temperatures above 70°F substantially increase the risk of heat-related dizziness 2

When to Seek Medical Evaluation

• Persistent dizziness despite adequate hydration and electrolyte replacement requires further medical evaluation 1
• New neurological symptoms (altered consciousness, focal deficits, severe headache) accompanying dizziness warrant immediate medical attention 2
• Progressive worsening of symptoms despite intervention should prompt evaluation for other causes of dizziness 1
• If dizziness has qualities of true vertigo (spinning sensation) rather than lightheadedness, consider vestibular causes that may require specific testing 3, 7, 4

Practical Implementation Algorithm

1. Measure your baseline weight and calculate sweat rate by weighing before and after typical 12 km runs 1
2. Implement pre-run hydration: 6 mL/kg body weight every 2-3 hours before running 1
3. During runs over 1 hour: Consume 0.5-0.7 g/L sodium solution with 30-60 g/hour carbohydrates 1
4. Post-run: Replace 100-150% of weight lost through fluids with electrolytes 1
5. Monitor response: If dizziness persists, increase sodium to 1.5 g/L and ensure you're not overdrinking 1
6. Avoid NSAIDs and ensure 2+ hours between meals and running 5, 2