Why Winter Training Quietly Increases Dehydration Risk

As winter arrives with colder environments, many athletes notice a simple change: they feel less thirsty. Drink bottles arrive home fuller, and hydration seems less of a priority than in summer. However, this reduction in thirst does not necessarily reflect a lower physiological need for fluids. Instead, it reflects a well-documented physiological response known as cold-induced thirst suppression.

Understanding this phenomenon is important for maintaining training consistency, cardiovascular stability and recovery during winter months, when under-hydration can occur unnoticed.

What is cold-induced thirst suppression?

The decrease in perceived thirst that happens when exposed to cold environments, even when fluid losses are continuing, is known as "cold-induced thirst suppression." This reaction has been regularly seen both at rest and during cold-weather exercise (Kenefick et al., 2003).

The mechanism is primarily cardiovascular rather than behavioural. Exposure to cold causes peripheral vasoconstriction, shifting blood from the extremities to the centre of the body. This temporary increase in blood volume in this part of the body is detected by receptors that interpret it as adequate circulatory filling. As a result, thirst is reduced, and the secretion of arginine vasopressin (AVP), a hormone involved in fluid regulation, may be suppressed (Kenefick et al., 2003).

It is important to note that this response occurs regardless of the body's actual state of hydration. In other words, in cold climates, thirst becomes a less accurate indicator of the need for hydration.

Fluid losses still occur in cold environments

While thirst is reduced, fluid losses do not stop. Athletes continue to lose water through several pathways:

Sweat

Although sweat rates are often lower in cold environments compared with hot conditions, sweating still occurs during exercise, particularly when intensity is moderate to high or when layered clothing limits evaporative heat loss (Freud and Sawka, 1996). Sweat evaporation may also mask the perception of sweating, leading athletes to underestimate fluid loss.

Respiratory water loss

Cold air is usually drier, which significantly increases water loss through the respiratory tract. Each breath must be humidified and warmed before reaching the lungs, which increases water loss through the respiratory tract compared to warmer conditions (Freud and Sawka, 1996).

Cold-induced diuresis

Exposure to cold can increase urine production due to altered renal blood flow and hormonal changes. Although this effect is more pronounced at rest than during exercise and is affected by several factors such as intensity, hydration status, body composition, etc., it can contribute to a negative water balance during prolonged exposure to cold (Freud and Sawka, 1996).

Taken together, these mechanisms mean that athletes can enter or leave training sessions with a meaningful fluid deficit, despite reporting little or no thirst.

Why thirst becomes an unreliable guide in winter

Thirst is sometimes a useful but imperfect regulator of fluid intake. Even in mild conditions, thirst often lags behind fluid loss and does not fully protect against dehydration during exercise (Kenefick, 2018; ACSM et al., 2007). Often, when we feel thirsty, it is because we are already dehydrated.

Exposure to cold further weakens this feedback loop. Experimental studies show that people drink significantly less fluid during and after exercise in cold conditions compared to warmer conditions, despite similar or continuous fluid losses (Mears and Shirreffs, 2014). This creates a mismatch between intake and physiological needs.

As a result, athletes may complete sessions feeling subjectively comfortable, while the underlying hydration status progressively deteriorates over days or weeks of winter training.

Implications for performance and recovery

Dehydration, which is usually defined as a loss of more than 2% of body weight, has well-established physiological consequences, and although these are mostly more pronounced in hot environments, they also affect athletes that train in colder environments. 

These include:

• Reduction in plasma volume.

• Increase in cardiovascular stress.

• Increase in heart rate for a given workload.

• Increased perceived exertion.

• Impaired endurance performance and recovery.

(Cheuvront et al., 2003; Maughan and Shirreffs., 2010)

Cold environments do not protect athletes from these effects. In fact, because subjective signals are attenuated, stress related to dehydration may go unnoticed until training quality or recovery begins to decline.

For endurance athletes who train frequently during the winter, this can subtly affect the consistency of sessions, pace accuracy, recovery between sessions, and tolerance to accumulated training load.

Why winter is a high-risk period for under-hydration

Several factors combine to make winter one of the easiest times to fall behind on hydration:

• Suppressed thirst perception

• Increased indoor training, often with limited airflow

• Layered clothing masks sweat loss

• Reduced habitual drinking behaviour

• Shorter sessions that “don’t feel demanding”

Individually, none of these guarantees dehydration. Collectively, they increase the likelihood that fluid intake does not match fluid loss over time.

Practical perspective

The key message from the science is not that athletes should drink excessively in winter, but that thirst alone may be insufficient as a guide. Awareness of cold-induced thirst suppression allows athletes to approach hydration more deliberately, particularly around training sessions.

Maintaining consistency in fluid intake before, during and after sessions — rather than relying solely on perceived thirst — is likely to support more stable hydration status across the winter training period.

References

American College of Sports Medicine, Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and Science in Sports and Exercise, 39(2), 377–390. 

Cheuvront, S. N., Carter, R., 3rd, & Sawka, M. N. (2003). Fluid balance and endurance exercise performance. Current Sports Medicine Reports, 2(4), 202–208. 

Freund, B. J., & Sawka, M. N. (1996). Influence of cold stress on human fluid balance. In B. M. Marriott & S. J. Carlson (Eds.), Nutritional Needs in Cold and in High-Altitude environments: Applications for Military Personnel in Field Operations (Chapter 9, pp. 161–179). National Academies Press.

Kenefick R. W. (2018). Drinking Strategies: Planned Drinking Versus Drinking to Thirst. Sports Medicine (Auckland, N.Z.), 48(Suppl 1), 31–37. 

Kenefick, R. W., Hazzard, M. P., Mahood, N. V., & Castellani, J. W. (2004). Thirst sensations and AVP responses at rest and during exercise-cold exposure. Medicine and Science in Sports and Exercise, 36(9), 1528–1534. 

Mears, S. A., & Shirreffs, S. M. (2014). Voluntary water intake during and following moderate exercise in the cold. International Journal of Sport Nutrition and Exercise Metabolism, 24(1), 47–58. 

Maughan, R. J., & Shirreffs, S. M. (2010). Dehydration and rehydration in competative sport. Scandinavian Journal of Medicine & Science in Sports, 20 Suppl 3, 40–47.