Dehydration is a common, often minimized, problem. However, its effects can disrupt the entire body's balance.
But how do you know if you are affected? How do you reliably calculate your water deficit? And above all, what can be done to correct it effectively, without error?
In this article, you will discover the causes, the signs to watch for, the calculation formula to use, and simple solutions to maintain a stable water balance in all circumstances!
What is water deficit?
From a physiological perspective, a water deficit refers to a decrease in the volume of water available in the body . It reflects an imbalance between intake (water, food, drinks, etc. ) and water loss (sweat, urine, respiration , etc. ).
When this deficit involves both water and electrolytes, such as sodium, it is referred to as global or isotonic dehydration .
If water losses are greater than sodium losses, then this is a free water deficit .
Conversely, if the body loses more salt than water, this is called intracellular dehydration (or sodium deficiency).
Understanding these different types of water deficit is therefore essential for adapting care.
What are the causes of a water deficit?
Insufficient hydration is the most common cause.
This is often the case if you forget to drink properly or if your intake is low during a heat wave or prolonged fasting.
The deficit can also result from excessive losses, particularly in cases of:
- high fever or excessive sweating ;
- diarrhea or vomiting ;
- prolonged hyperventilation (stress, intense effort).
These different physiological states alter the function of water regulation.
Furthermore, certain treatments, such as diuretics or laxatives, can worsen fluid loss or limit its replacement . The same is true for certain chronic diseases such as diabetes or kidney failure .
What are the symptoms of dehydration?
The signs are generally the same, regardless of the cause of the fluid imbalance . The first indicator is often intense thirst , signaling that your body is demanding water.
You may also notice:
- dryness of the mouth and tongue;
- darker and less abundant urine ;
- headaches, unusual fatigue or a feeling of confusion.
Other symptoms should also alert you, such as persistent skin folds after pinching or rapid weight loss. These often indicate advanced dehydration .
Be especially careful if you are in the company of elderly people , sick people or young children .
How do you calculate the water deficit?
Formula for calculating water deficit
To calculate the water deficit, professionals use a Standard formula . It is based on two elements: your weight and your sodium level (sodium level in the blood).
Water deficit (in L) = Weight (kg) × 0.6 × [(measured sodium / 140) – 1]
The coefficient 0.6 corresponds to the proportion of water in the body of an adult male. This figure varies according to age and sex:
- 0.5 for an adult woman;
- 0.6 for a child;
- 0.45 - 0.5 for an elderly person.
Example of a practical calculation
Let's take the case of a 70 kg patient with a serum sodium level of 160 mmol/L:
Deficit = 70 × 0.6 × [(160/140) - 1]
Deficit = 70 × 0.6 × (1.14 - 1)
Deficit = 70 × 0.6 × 0.14 = 5.88 liters
This person has a water deficit of approximately 5.9 L. This is the volume of free water that needs to be compensated for.
Useful tools: automatic calculator
There are online calculators that simplify the calculation of water deficit. The most reliable resources are:
- Medicalcul Calculation of the water deficit
- MDCalc – Hypernatremia correction
Please note that these tools are intended for healthcare professionals. You should only use them if you know your precise data (weight, sodium levels). If in doubt, it is always best to consult a doctor.
Medical implications of poorly compensated fluid deficit
An uncorrected water deficit can have serious consequences .
In the short term, you risk extracellular dehydration , which can cause hypernatremia. (excessive concentration of sodium in the blood) . This can cause confusion, seizures, or even a coma in extreme cases.
In the long term, an inadequately compensated water deficit can lead to:
- the formation of kidney stones;
- recurrent urinary tract infections ;
- kidney failure .
Even moderate dehydration can decrease your ability to concentrate , your energy levels, and your physical performance . In athletes , it increases the risk of muscle cramps , decreased performance, or slower recovery.
Vulnerable people (children, seniors, chronically ill patients) are particularly at risk. They are less able to perceive thirst and lose water more quickly.
How to prevent or correct a water deficit?
Prevention measures
The best solution for stabilizing the water balance remains prevention.
You should drink regularly throughout the day , without waiting until you are thirsty.
A healthy adult should consume on average between 1.6 and 2 liters of water per day . However, these needs should be adjusted according to individual circumstances: age, activity level, climate , etc.
Therefore, you can increase your water intake in case of fever, intense heat, or physical activity.
However, be careful not to drink too much plain water: an excess can lead to hyponatremia (low sodium concentration in the body).
Monitor the color and quantity of your urine: it should be clear and abundant.
Also ensure that vulnerable people around you (the sick, elderly relatives , etc. ) stay well hydrated. Children's water needs are higher, especially during their years of rapid growth.
Appropriate treatment
If the deficit is mild or moderate, a oral rehydration This is sufficient in most cases. Therefore, you can:
- drink mineral water, electrolyzed drinks.
- Opt for oral rehydration solutions ( ORS ). These are formulated to effectively compensate for losses (electrolytes, glucose , etc. ). Drink in small sips, regularly, rather than large quantities all at once.
In cases of severe deficiency, intravenous rehydration may be necessary. This is only performed under medical supervision using isotonic or slightly hypotonic solutions, depending on the situation.
The correction of serum sodium levels must be gradual to avoid any risk of cerebral edema and other complications.
Once rehydration has begun, monitoring is essential:
- Monitoring of blood sodium levels
- Monitoring of weight and urine volume
- Neurological assessment
Biological monitoring allows for the adjustment of administered volumes and avoids overcorrection.
In summary: proper hydration is the key to maintaining the body's balance.
Water deficiency constitutes a serious imbalance that can affect all vital functions if its correction is neglected.
Knowing how to calculate its value then allows for effective guidance of care, whether in a medical setting or for better daily management.
Prevention remains the best strategy: drinking regularly, adapting your intake according to your needs and monitoring for warning signs are good habits to adopt.
Mini checklist:
- Do I often feel thirsty?
- Is my urine clear and plentiful?
- Am I tired for no reason?
- Do I have a dry mouth?
If you answer "yes" to several of these questions, or if you have any doubt about your hydration level, do not hesitate to consult a healthcare professional.
Summary table: symptoms / calculation / actions to take
|
Symptoms |
● Intense thirst ● Dry mouth ● Dark and scanty urine ● Fatigue ● Headaches ● Confusion ● Persistent skin fold ● Rapid weight loss |
|
Deficit calculation |
Deficit (L) = Weight (kg) × coefficient × [(measured sodium / 140) – 1] Coefficients: Male 0.6; Female 0.5; Child 0.6; Elderly 0.45–0.5 |
|
Actions to be taken |
● Drink regularly, without waiting until you are thirsty ● Oral rehydration (water, electrolyte drinks, ORS) ● Intravenous rehydration if severe deficit, under medical supervision ● Monitor serum sodium, weight, urine, and neurological status ● Consult a professional if you experience significant symptoms |
Bibliography
Cheuvront, SN, & Kenefick, RW (2014). Dehydration: physiology, assessment, and performance effects. Nutrients, 6(11), 4481-4493.
https://doi.org/10.1002/j.2040-4603.2014.tb00543.x
Cheuvront, SN, Kenefick, RW, Sollanek, KJ, Ely, BR, & Sawka, MN (2013). Water-deficit equation: systematic analysis and improvement. American Journal of Clinical Nutrition, 97 (1), 79–85. linkinghub.elsevier.com/retrieve/pii/S0002916523053753
Agrawal, V., Agarwal, M., Joshi, SR, & Ghosh, AK (2008). Hyponatremia and hypernatremia: Disorders of water balance. Journal of the Association of Physicians of India, 56 (12), 956–964. https://pubmed.ncbi.nlm.nih.gov/19322975/
Casa, DJ, Armstrong, LE, Hillman, SK, Montain, SJ, Reiff, RV, Rich, BS, Roberts, WO, & Stone, JA (2000). National Athletic Trainers' Association position statement: fluid replacement for athletes. Journal of Athletic Training, 35 (2), 212–224.
https://pmc.ncbi.nlm.nih.gov/articles/PMC1323420/
Guerrant, RL, Deboer, MD, Moore, SR, Scharf, RJ, & Lima, AAM (2020). Rehydration in children. In StatPearls . Stat Pearls Publishing.
https://www.ncbi.nlm.nih.gov/books/NBK555956/
Popkin, B.M., D'Anci, KE, & Rosenberg, IH (2010). Water, hydration, and health. Nutrition Reviews, 68 (8), 439–458.
