Winter Hydration

Recently a team asked if we had any cold weather riding tips and whether they should fuel with gels and bars rather than drinks for their base miles when the temperature drops.  When it gets very cold, riders tend not to be so thirsty and sometimes bottles can even freeze which creates more practical obstacles.  However, cold weather riding and modern living conditions can create challenges to hydration status that may have implications from the ability to burn fat to how easy it is to keep fingers warm.

Many years ago, I remember working with a Sport Scientist/nutritionist at a premier league football club.  He had been monitoring the player’s hydration status throughout the year from the hot pre-season training sessions through the colder winter months.  To his surprise he found that the hydration status of the players was much better during the hotter parts of the year than the winter months.

One explanation of the poor hydration status in the winter months was a possible lack of awareness of the importance of hydration in the cold compared to the hot summer months.  Usually we tend to equate the importance of hydration, or staying hydrated with hot conditions due to fluid losses in sweat which we can visualise.  This and the less appealing nature of consuming chilled soft beverages in the cold probably means that we are all a little guilty of neglecting our hydration needs in the winter months.

An understanding of how modern lifestyles and physiological reactions to cold exposure can combine to influence hydration status is possibly the first step towards optimising an important parameter in health and performance.

Many people may have noticed an increased desire to urinate when exposed to cold temperatures, perhaps whilst waiting for a bus or train dressed more for the office than outdoor conditions.  This is a physiological phenomenon known as Cold Induced Diuresis (CID) first noted in the scientific literature over 200 years ago (Sutherland, 1764) yet still not fully understood.  One possible mechanism is that peripheral vasoconstriction due to cold exposure increases blood pressure causing the kidney to increase fluid and sodium excretion (Freund & Sawka, 1994).

Fluid losses due to CID may be more significant during rest or low intensity exercise, typical of a morning commute, than high intensity exercise.  CID is often thought to be self-limiting however, modern lifestyles often mean that CID is followed by entry into a hot air conditioned office or centrally heated house with different hydration challenges.  These challenges could further compromise hydration status unless fluids and electrolytes are replaced.

Once cold dry air enters a hot building the water carrying capacity of the air increases, acting as a desiccant for anything (and anyone) stabilized to a higher relative humidity.  Museums and other buildings where fine paintings and artefacts are kept, go to great lengths to ensure stable humidity to stop then drying out and cracking.  Unfortunately, the same attention to humidity is seldom taken for many work or indoor exercise environments.  Office buildings heated with forced air without a humidifier can have a relative humidity of 13% making the environment considerably drier than Death Valley (23%) or the Sahara Desert (Bas, 2004). Dry eyes, nose and throat is often the consequence of working in this kind of environment, which may at least serve as reminder to consume fluids.

Similar ‘insensible water loss’ is often more visible in the vapour trail left by exhaled breath in cold air.  When cold dry air enters the lungs, it is heated by the body which increases the moisture carrying capacity of the air.  The effect of this is that air leaving the lungs contains more moisture than that inhaled and presents additional fluid losses which need to be accounted for.  The amount of fluid lost in this way depends on the relative humidity of the air AND the amount of air entering and leaving the lungs.  The amount of fluid lost in this way could be quite significant for people exercising for long durations at high work rates, typical examples being cyclists and long distance runners.

High work rates may also result in high sweat rates irrespective of climactic conditions and these may be further enhanced by cold weather clothing.  Research on military personnel in cold weather gear has shown that little sweat is produced at rest, yet even moderate exercise in the same gear could result in sweat losses of nearly 2 litres per hour (Freund & Sawka, 2016).

Although significant advances have been made to improve the breathability of cold weather sportswear most hikers and cyclists are aware of the ‘boil in the bag’ effect of waterproof clothing when working at high work rates.  Whilst it is important to modulate clothing according to exercise intensity, in practice this can be difficult.  One thing the professionals become very good at is quickly adding or removing layers whilst on the move but is seldom an exact science.  The resulting sweat rates may result in more sweat fluid losses during exercise in the cold than in more temperate conditions.  It is worth checking body mass before and after exercise sessions in the cold to get an idea of fluid losses during exercise.

COLD HANDS AND FEET

One of the biggest challenges to cycling in the cold is keeping hands and feet warm.  In conditions where core temperature is maintained but peripheral temperatures become sufficiently low a paradoxical cold induced vasodilation (CIVD) is often observed.  This mechanism is thought to be one that protects against cold injury and can often be observed to exert a cyclical pattern where periods of vasoconstriction are followed by dilation and an increase in finger blood flow and temperature.  This cyclical pattern was first observed by Lewis in 1930 who termed it the hunting response (Daanen & Van Marken Lichtenbelt, 2016).   

Dehydration is often cited as a risk factor in cold injury and some early research suggests that once plasma volume is sufficiently compromised there is insufficient blood volume to increase finger temperature through CIVD (O'Brien, Young, & Sawka, 1996).   Whilst the reasoning may seem reasonable laboratory studies have been unable to demonstrate any consistent pattern.  However, as is often the case, it is difficult to replicate the extreme wind-chill, high work rates and exercise durations of practical winter training in the laboratory. Winning the battle to maintain comfort and focus during those long cold winter may be one more reason to review your hydration status. 

MAN UP – GET USED TO IT?

Unfortunately, field studies with cold exposure suggest poor adaptability and even the possibility of repeated exposures resulting in reduced finger blood flow and a continued risk to cold injury and discomfort (CHEUNG & Daanen, 2011).  Fortunately, technological advances in clothing have made it easier to keep fingers and toes warm.  Maintaining good hydration status may help and is unlikely to make things worse.  Readers should also consider the concluding remarks from a recent review, which perhaps make a good case for indoor trainers and virtual reality cycling!

‘Humans have developed excellent clothing, houses and behavioral adaptations to cold, and these seem to be tremendously more important for living under extreme conditions than our physiological mechanisms alone.’

Daanen & Van Marken Lichtenbelt, 2016 

Whilst there has been recent lively debate as to the importance of hydration status for acute sports performance in the scientific journals and it is important to emphasis the dangers of over hydration (Wall et al., 2013). Over hydration, water intoxication or more technically hyponatremia is possibly more of a risk factor in hot conditions and indoor cycling.   It is generally accepted that chronic dehydration is detrimental to health and adaptation to exercise. Dehydration may increase the catabolic effects of exercise and possibly reduce the ability to burn fat which is counter to the adaptations often sought from the winter training period (Keller, Szinnai, Bilz, & Berneis, 2003).   Other researchers have shown that dehydration may compromise immune function which is often challenged during the winter months (Chishaki et al., 2012).  Some very recent research suggests that dehydration may increase pain perception, whilst far from a sports study it may mean that dehydration could further add to the pain of those hard winter miles (Bear, Philipp, Hill, & Mündel, 2016). 

The particular combination of cold weather exposure and modern lifestyles can often combine to increase the risk of dehydration before exercise has even started.

Careful thought on the application of hydration strategies is likely to improve health, performance and enjoyment for exercise participation.

STRATEGIES

Secret-Training TRAINING MIX is ideal for keeping hydrated during winter training miles.  Its unique combination of slow release carbohydrates is ideal for fat burning exercise and contains electrolytes to optimise hydration.  This combination is also unlikely to freeze in bottle unlike water!

It is always good form to take more energy gels out with you than you intend to use, just in case you are out longer than intended or miscalculate on energy needs.  This is even more important during winter months as the energy boost from an energy gel can also help with heat production.  Given that hydration is likely to be compromised isotonic gels are possibly best for this purpose, thought the positive effects on caffeine on mood may have other benefits.

Whilst people often try to limit carbohydrate supplementation during winter rides, in order to improve body composition, when conditions are really tough it may be best to consume more carbohydrate to help to keep warm and complete the required training.

Remember energy drinks can be made up with hot water (or even hot tea) and thermal drinks bottles are available if you do not have a convenient DS to hand up a drink when required, though these do reduce the volume of fluid that can be carried.

References

Bas, E. (2004). Indoor air quality (1st ed., pp. 156-157). Lilburn, Ga.: Fairmont Press.

Bear, T., Philipp, M., Hill, S., & Mündel, T. (2016). A preliminary study on how hypohydration affects pain perception. Psychophysiology, 53(5), 605-610. http://dx.doi.org/10.1111/psyp.12610

CHEUNG, S. & Daanen, H. (2011). Dynamic Adaptation of the Peripheral Circulation to Cold Exposure. Microcirculation, 19(1), 65-77. http://dx.doi.org/10.1111/j.1549-8719.2011.00126.x

Chishaki, T., Umeda, T., Takahashi, I., Matsuzaka, M., Iwane, K., & Matsumoto, H. et al. (2012). Effects of dehydration on immune functions after a judo practice session. Luminescence, 28(2), 114-120. http://dx.doi.org/10.1002/bio.2349

Daanen, H. & Van Marken Lichtenbelt, W. (2016). Human whole body cold adaptation. Temperature, 3(1), 104-118. http://dx.doi.org/10.1080/23328940.2015.1135688

Freund, B. & Sawka, M. (1994). Human Fluid Balance and Dehydration During Cold Weather Military Operations (1st ed.). Ft. Belvoir: Defense Technical Information Center.

Freund, B. & Sawka, M. (1994). Human Fluid Balance and Dehydration During Cold Weather Military Operations (1st ed.). Ft. Belvoir: Defense Technical Information Center.

Freund, B. & Sawka, M. (2016). Influence of Cold Stress on Human Fluid Balance (1st ed.). Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK232870/

Institute of Medicine, M., Marriott, B., & Carlson, S. (1996). Nutritional Needs in Cold and High-Altitude Environments (1st ed., pp. Chapter 9, Influence of Cold Stress on Human Fluid Balance161-180). Washington: National Academies Press.

Keller, U., Szinnai, G., Bilz, S., & Berneis, K. (2003). Effects of changes in hydration on protein, glucose and lipid metabolism in man: impact on health. European Journal Of Clinical Nutrition, 57, S69-S74. http://dx.doi.org/10.1038/sj.ejcn.1601904

Marriott, B. & Newberry, S. (1996). Nutritional needs in cold and in high-altitude environments. Washington, D.C.: National Academy Press.

O'Brien, C., Young, A., & Sawka, M. (1996). HYPOHYDRATION AND THERMOREGULATION IN COLD AIR 1208. Medicine &Amp Science In Sports &Amp Exercise, 28(Supplement), 203. http://dx.doi.org/10.1097/00005768-199605001-01206

Sutherland, A. (1764). An attempt to ascertain and extend the virtues of Bath and Bristol waters by experiments and cases. By Alex. Sutherland .. (1st ed.). London: Printed for W. Frederick and S. Leake, Bath, and sold by Messrs. Hawes and Co., and W. Johnston [London].

Wall, B., Watson, G., Peiffer, J., Abbiss, C., Siegel, R., & Laursen, P. (2013). Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat. British Journal Of Sports Medicine, 49(16), 1077-1083. http://dx.doi.org/10.1136/bjsports-2013-092417