Myth-Busting Hydration
Should we be drinking 8 glasses of water every day?
By Laura Jennings
We’ve all been told to have eight glasses of water every day to stay hydrated, but what’s the truth in that and when might hydration needs vary? We’ve invited Laura Jennings, who has a Masters in Nutrition, to share ideas around how body composition and physical activity levels aren’t the only factors to be taken into consideration.
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Why is hydration important?
Water is essential for survival. It is a critical nutrient that is important in regulating body temperature, transporting nutrients, the removal of waste and maintaining bodily functions.
Water makes up approximately 45%-75% of human body weight. ‘Hydration’ refers to maintaining water balance, which is the difference between water intake and how much water we lose.
When water loss in the body fails to be replaced it is described as “dehydration”. Dehydration has been associated with a reduction in both long and short-term memory, attention deficits and spatial awareness.
Mild dehydration leads to fatigue and headaches, while severe dehydration can be fatal.
To maintain hydration and prevent dehydration health experts recommend drinking 8 glasses of water a day, which is the equivalent of about 2 litres.
“Is 8 glasses of water’ a day true for everyone?”
Why hydration needs vary
Individual hydration needs vary depending on a variety of factors, including, body composition, physical activity levels, levels of salt present in the diet and environmental factors. It is challenging to make general recommendations about the amount of water a person should consume for optimum hydration. Just as there is recent evidence demonstrating the importance of personalized nutrition, hydration requirements should also be personalized as much as possible to determine accurate intakes.
Body composition
Total water intake varies depending on body mass with a larger body mass requiring a higher water intake than those with a lower body mass. Studies have shown that higher levels of water intake are associated with a lower BMI. Increasing water balance in the human body has been identified as a potential useful strategy in the prevention of obesity.
Environmental Factors
In warm climates, water loss through sweat is an essential cooling mechanism. Sweat production depends on environmental temperature, humidity and the type of clothing a person wears. Water losses through sweat can range from 0.3L/h when individuals are sedentary to 2.0L/h in high activity in the heat. Therefore, intake requirements in hot climates can range from 3L/d in adults under normal conditions to 6L/d in extreme heat.
Physical Activity Levels
Fluid and electrolyte replacement is key in physically active people to compensate for water losses that occur through sweat. Therefore, total water intake requirements are higher among athletes and those with higher physical exertion. In order to maintain athletic performance and facilitate recovery from exercise increasing fluid intake above the recommended ‘8 glasses per day’ is strongly recommended. Quantifying sweat rates for physically active individuals will give a more accurate indication of total water intake requirements.
Sodium Intake
Diets high in salt have been associated with better hydration status. Generally, eating salty foods induces thirst and leads to greater fluid ingestion. There is some evidence that shows that diets high in salt induce body water conservation. However, it should be noted that diets high in sodium are associated with hypertension, stroke and cardiovascular disease. Therefore, salt intakes above the recommended intake levels (6g/day) are not recommended as part of a healthy diet.
Dietary sources of water
Food provides approximately 20% of our water content and this can vary depending on the type of food consumed. For instance, high fibre foods, such as fruit and vegetables comprise on average 80% water compared to carbohydrates and confectionary, which are made up of around 10%. It is important to note that fibre draws water into the gut forming a gel; therefore adequate water intake is essential to prevent constipation when consuming foods high in fibre.
The main dietary sources of water come from the drinks we consume. All drinks contribute to water levels in the human body. However our drink of choice can have other health impacts, including our dental health and energy levels.
With record heat in the UK, proper hydration is key to regulating body functions and keeping us energized. Here at the Be Well we’ve come up with a nutrient-filled hydration smoothie for these hot summer days:
1/2 cup of coconut water
1/2 cup of milk of choice
1 banana
1 handful of blueberries
1 tablespoon of chia seeds
1/2 tbsp of peanut butter
1 handful of fresh / frozen spinach
1 handful of cashew nuts
ABOUT THE AUTHOR:
Laura Jennings
After five years working in the corporate world in luxury fashion and technology, Laura trained as a yoga teacher and joined the team at My Method, curating exciting and diverse wellbeing programmes for private clients and corporates.
Laura has a passion for holistic wellbeing and nutrition and has joined the Be Well team to support with content creation, workshop development and more. She is progressing in the world of health and wellness and has recently completed a Masters in Nutrition at King's College London.
References
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2. Armstrong, L.E., Johnson, E.C. (2018). Water Intake, Water Balance, and the Elusive Daily Water Requirement. Nutrients. 10(12):1928.
3. Rakova, N., Kitada, K., Lerchl, K., Dahlmann, A., Birukov, A., Daub, S., Kopp, C., Pedchenko, T., Zhang, Y., Beck, L., Johannes, B., Marton. A., Müller, D.N., Rauh, M., Luft, F.C., Titze, J. (2017). Increased salt consumption induces body water conservation and decreases fluid intake. Journal of Clinical Investigation,127(5):1932-1943.
4. McDermott, B.P., Anderson, S.A., Armstrong, L.E., Casa, D.J., Cheuvront, S.N., Cooper, L., Kenney, W.L., O'Connor, F.G., Roberts, W.O. (2017). National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. Journal of Athletic Training, 52(9):877-895.
5. Popkin, B.M., D'Anci, K.E., Rosenberg, I.H. (2010). Water, hydration, and health. Nutrition Revolution, 68(8):439-58.
6. Goncalves, C., Abreu, S., Padrao, P., Pinho, O., Graca, P. (2015). Association between sodium excretion and hydration status by Free Water Reserve: a cross-sectional analysis in adolescents. BMC Nutrition, 1(17), 1-8.
7. Benelam, B., Wyness, L. (2010). Hydration and health: a review. Nutrition Bulletin, 35(1), 3-25