Altitude Sickness Prevention

How Altitude Affects Your Body

At sea level: 21% oxygen at 1 atmosphere. At 5,895m: still 21% oxygen but 0.5 atmospheres. Your body gets half the oxygen per breath.

Timeline

1. Hours 1–4: Faster breathing, higher heart rate
2. Hours 6–12: Increased urination, restless sleep
3. Days 2–4: Peak symptoms (headache, nausea), then improve
4. Days 4+: Body adapts. Symptoms fade if route has good acclimatization

This is acclimatization—it takes days, not hours. Routes with extra time (Lemosho, Northern Circuit) give your body time to adapt safely.

What the Research Says About Acclimatization

The most robust data on altitude acclimatization comes from the US Army's research on soldiers deployed to high altitude in the 1970s and 80s. The findings remain the foundation of modern altitude medicine: the human body can adapt to altitude, but the adaptation requires time and cannot be accelerated beyond a physiological limit.

The 48-Hour Rule

After ascending above 2,500m, the kidneys begin excreting bicarbonate to correct blood pH — this is the primary mechanism of altitude acclimatization. The process takes 48 to 72 hours to complete at any given altitude. This is why sleeping at the same elevation for 2 consecutive nights is more valuable than ascending and descending repeatedly. Any itinerary that moves your sleeping elevation more than 500m per day above 3,000m is cutting against the physiology.

The Oxygen Cascade at 5,895m

At sea level, oxygen constitutes 21% of the atmosphere and barometric pressure delivers approximately 160 mmHg of oxygen partial pressure to the lungs. At Uhuru Peak (5,895m), barometric pressure is roughly 355 mmHg — half sea level. The oxygen percentage is unchanged (still 21%) but the partial pressure of oxygen is approximately 70 mmHg. This means lung diffusion — the transfer of oxygen from air into the bloodstream — operates at roughly 50% efficiency compared to sea level. Acclimatization improves this by increasing lung diffusion capacity and blood hemoglobin concentration, but it cannot fully compensate.

Three Pillars of Prevention

Supplements and Altitude: What Helps, What Does Not

Beyond Diamox, several supplements are marketed for altitude performance. Here is what the evidence shows:

The most evidence-based approach: proper itinerary design, slow ascent pace, adequate hydration, and Diamox if your doctor approves. Supplements are secondary.

Who Is at Higher Risk?

Some climbers carry higher altitude risk regardless of fitness. Know your profile before choosing an itinerary:

• Prior AMS: If you had AMS symptoms at altitude before, you are statistically more likely to experience it again. Choose a longer itinerary.
• Fast ascent history: Climbers who have rushed altitude in previous trips tend to have accumulated risk. Slow down deliberately.
• Age under 30: Paradoxically, younger climbers are at higher risk because they are more likely to push pace and dismiss early symptoms.
• Dehydration: Any factor that reduces plasma volume (alcohol, caffeine excess, insufficient fluids) worsens altitude adaptation.
• Upper respiratory infection: If you arrive at altitude with a cold, your already compromised oxygen uptake is further reduced. Delay the climb if possible.

Mount Kilimanjaro Climb reviews client health questionnaires before booking. If your profile indicates elevated risk, we will recommend a longer itinerary (Lemosho 9-day or Northern Circuit 10-day) and discuss Diamox use with your physician before departure.

Pre-Climb Preparation

6 Weeks Before

• Build aerobic fitness: 4–5 hours/week hiking/running/cycling
• See your doctor. Discuss Diamox if interested.
• Get travel insurance (must cover evacuation)

1 Week Before

• Rest. No heavy workouts.
• Increase water intake gradually
• If taking Diamox, start 1 day before departure

Day 1 on Mountain

• Walk extremely slowly
• Drink 1 liter by lunch, 1 by dinner
• Eat carbs: rice, pasta, bread, potatoes
• Sleep at first camp. Don't push higher day 1.