Nutrition, hydration, smoking

Hypoglycaemia

The brain runs almost entirely on glucose. At blood glucose <70 mg/dl, typical symptoms appear (ICAO Doc 8984 §II.7): tremor, sweating, hunger, poor concentration, visual disturbance, confusion, decreased consciousness. Hypoxia amplifies the effect.

Practice: eat carbohydrate-rich before long flights; keep snacks and water within reach on multi-hour legs. Crash diets, fasting and skipped meals are inappropriate before flying.

Dehydration

The cockpit environment is dry (cold low-pressure outside air, plus heating); breathing rate is elevated. A fluid loss of 2 % of body weight measurably impairs concentration, reaction time and heat tolerance; >5 % leads to circulatory issues (FAA-H-8083-25B §17).

Symptoms: thirst, headache, fatigue, dark/scant urine, cramps. Rule of thumb: ~0.25 l/h water; caffeine and alcohol don't count.

Smoking — carbon monoxide

Tobacco smoke contains carbon monoxide (CO), which binds haemoglobin ~250× more avidly than O₂. Heavy smokers typically carry 5–10 % COHb; passive smokers 1–2 %; non-smokers <1 % (ICAO Doc 8984 §I.4).

Consequence: effective oxygen-carrying capacity is reduced; a smoker's "physiological altitude" at sea level is closer to 1,500–2,000 m. Add real altitude (3,000–4,000 ft) and noticeable hypoxia appears (see [[stadien-der-hypoxie]]).

CO can also leak from a faulty cabin heater — a CO detector is recommended.