Cold-weather running
Evidence: moderate
Cool conditions help performance, but genuinely cold air does not; the optimum for distance racing is a low band, not the coldest day. The popular fear that cold air damages healthy lungs is a myth: the real respiratory issue is airway drying and bronchoconstriction. The manageable risks are frostbite and hypothermia, governed by wind chill and wet, and they are handled with layering and covering up.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Cool helps, cold does not
Air temperature is the environmental factor with the biggest effect on marathon times, and performance is best in cool conditions, falling as it warms and also at the cold end (El Helou et al. 2012). “Cool” is the operative word. The optimum for fast racing is a low band rather than a single figure, and recent record-level analysis puts it higher than the often-quoted 8 to 12°C, varying by dataset, sex and pace (Scheer et al. 2021). Below that band, very cold air tends to impair comfort and economy, so colder is not faster. Cool conditions help mainly by reducing the heat strain covered under thermoregulation, the opposite problem to heat.
The lungs do not freeze
The common worry that cold air freezes or damages the lungs does not hold for healthy people. The upper and central airways warm and humidify inspired air before it reaches the lower airways, which stay close to body temperature even in deeply sub-zero air (Sjöström, Kennedy et al. 2020). The genuine respiratory issue is different: high ventilation of cold, dry air dries and cools the airway surface, which can trigger exercise-induced bronchoconstriction, and this is markedly more common in winter-endurance athletes than in the general population. Covering the mouth and nose with a buff or a heat-and-moisture-exchanging mask blunts that airway response in very cold air (Eklund et al. 2022).
The real risks: frostbite and hypothermia
The risks worth respecting are to skin and core temperature, and both are driven by wind chill and wet, not air temperature alone. Frostbite of exposed skin depends on wind chill and exposure time, and does not occur above freezing; hypothermia becomes a real risk when you are wet, exposed to wind, or slowing or stopping, since heat production falls while heat loss continues (NOAA). The practical management follows directly:
- Layer moisture-wicking inner layers under a wind- and water-resistant shell, and adjust for the windchill, not the thermometer.
- Cover the extremities most prone to frostbite and heat loss: hands, ears and face.
- Warm up before starting, and keep moving; the danger climbs if an injury or a long event forces you to slow.
- Plan routes and kit so a mechanical problem does not leave you stationary and wet far from shelter.
Most cold-weather risk is manageable with sensible kit. The fear to discard is frozen lungs; the risks to plan for are wind chill, wet and being caught out when you stop.