Our bodies are comprised of 60% water on average and maintaining hydration status has impacts
on health and well-being in addition to sports performance. Furthermore, we can obtain water from a variety of sources and making the right choices can have significant implications both in and outside of competition. Although severe dehydration is rare in the absence of disease, acute mild dehydration is relatively common in the UK and affects physical and cognitive function as well as causing fatigue and headaches. In the long term, it has also been associated with increased risk of constipation, urinary tract infections, hypertension and heart disease. Conversely, overhydration can lead to hyponatremia which can, in some circumstances, be fatal. There is huge variation between the fluid needs of individuals which can be further exacerbated by the impacts of different environments and activity levels. The result is often a confusing message as to how best to maintain hydration status. This two-part article discusses fluids and hydration. Part one considers the health implications on day-to-day life, whilst part two discusses hydration in the context of endurance sports.
Fluid Intake The current UK guidelines recommend drinking 6-8 glasses (1200-1600ml) of fluid a day. This includes water, milk, hot beverages such as coffee and soft drinks. It does not include alcohol. We also consume water in foods and on average obtain 20% of our fluids this way. There is a wide variation in food fluid content with foods such as fruit comprising around 90%, soups around 80% and breads 50% and choosing high water content foods can be especially helpful in controlling our calorie intake.
Sugary Drinks When not undertaking exercise we recommend obtaining fluids from low calorie sources (some examples are listed below). The reason for this is that our bodies are less able to detect the calories consumed in liquids than solids, leading to an increase in energy consumption and possible weight gain. Furthermore, sugar rich drinks (including soft drinks and fruit juices) have been associated with tooth decay. As endurance athletes, we are often reliant on a high sugar intake during training and competition. It is therefore especially important that we minimise health risks by making the right choices when we are not training. Excluding intake around training, we recommend avoiding sugar sweetened beverages and limiting fruit juices to one small glass (150ml) per day.
Alcohol and Caffeine Alcohol and caffeine both provide fluid but have also been reported to have diuretic effects. Overall the diuretic effect of caffeine is relatively small and unless consuming large amounts of very concentrated sources such as espressos, caffeinated drinks are net hydrating and count towards your fluid intake. Conversely, alcoholic drinks are excluded and can be particularly dehydrating in drinks such as spirits, where the alcohol content is high. Furthermore, alcohol is calorie dense (7 calories per gram) and, if consumed in excess, has serious health consequences. Recent UK guidelines on alcohol recommend a maximum of 14 units a week spread over at least 3 days. For many years a protective effect of moderate drinking against cardiovascular disease has been claimed. This is increasingly coming under question and association with increased risk of cancer at any level of consumption, alongside evidence of detrimental effects on sport performance, leads us to recommend consuming as little alcohol as is sustainably possible for you.
Monitoring your Hydration Status Urine colour has been widely used as an approximate indicator of hydration status and is proven to be reliable for monitoring hydration during day to do activity. An 8 scale colour chart is most commonly used (see below an example from the NHS), in which urine coloured between 1 and 3 indicates an individual is well hydrated, whilst colours matching 4 or above indicates dehydration.
Aim to drink 6-8 glasses of fluids per day
Minimise intake of sugary drinks and alcohol
Include foods with high fluid content such as fruit and vegetables
Monitor your hydration level and drink accordingly
Calories from Drinks
The graph below compare the calorific and macronutrient content of a different drinks per 100ml
Benelam, B.,Wynes, L. (2010), Hydration and health: a review. Nutrition Bulletin 35, 1,P3–25
Shirreffs, S. M. (2003). Markers of hydration status. Eur J Clin Nutr 57 Suppl 2 S6-9