How does dehydration occur?
You get dehydrated when you lose more water than you take in 1. An objective measure of dehydration is loss of body weight greater than 1% (0.7 kg in a 70 kg individual) 13.
1. Obligatory Water Loss
Obligatory water loss is water loss from your body you cannot prevent 2.
- A healthy, sedentary adult usually loses at least 1 liter of water per day with the urine, stool, breathing and invisible perspiration (sweating not included) 2.
- Obligatory water loss in physically active and in older individuals may reach 3 liters of water per day (sweating not included) 2.
The actual body water loss, which includes obligatory water loss plus sweating, is greater,usually at least 2 liters per day and may exceed 10 liters per day 2,13.
2. Not Drinking Enough
A general recomendation to drink at least eight glasses of fluid per day may be misleading:
- People whose diets are rich in fruits, vegetables and cooked cereals may need to drink no additional water.
- Workers in hot climates may need 3-4 liters of water per hour or more than 10 liters per day 11.
2.1. Water Not Available
Sometimes water is not available and sometimes is not safe to drink.
- In the western world, tap water is usually safe to drink but this depends on the local municipality.
- In various parts of Africa, Asia, Indonesia and South America, tap water may be contaminated with viruses, bacteria or parasites. Drinking such water can cause diarrhea and thus dehydration.
2.2. Decreased or Absent Thirst
Decreased or absent thirst may occur:
- Due to tiredness or anxiousness or due to preoccupation with work
- In elderly 6
- In cold environment 9 and after arriving at high altitudes 4
- In head injury, stroke, liver cirrhosis, birth defects, vasospastic syndrome 6
2.3. Inability to Drink
- Painful mouth or throat sores (yeast infection or oral thrush, candidiasis or moniliasis 24), strep throat, throat cancer
- Mouth or throat injuries or surgery
- Gastrointestinal obstruction: gastroparesis, gastric cancer
- Severe nausea during pregnancy or “morning sickness”
- Dementia 26
- Delirium 26
- Sedation 26
2.4. Unwillingness to Drink
- Hunger strike
- Anorexia nervosa or other psychological reasons, such as obsessive-compulsive disorder (OCD) 23
- An attempt to lose weight quickly (boxers before weighing).
- Depression 26
- Psychosis 26
3. Excessive Sweating
- High ambient temperature (summer, heat waves)
- Exercise in warm clothes, such as skiing in winter
- Prolonged, heavy physical work:
- Marathon runners can have sweating rate 0.5-3 liters per hour or more, so they can lose about 1.5-10 liters of water per marathon 17.
- Miners, workers in tropics can lose as much as 10 liters water during one shift 18.
- Fever, for example in flu, pneumonia, thyrotoxicosis, prolonged dancing after ecstasy use can also cause excessive sweating 20.
4. Prolonged Hyperventilation
Quite some water can be lost through breathing. Causes of prolonged hyperventilation:
- Heavy exercise
- Anxiety, hyperventilation syndrome
- High altitude 13
- Kidney disease, diabetic ketoacidosis (in poorly treated diabetes)
- Poisoning with salicylates (aspirin > 1 g/70 kg person) 14, amphetamine toxicity 19.
5. Repeated Vomiting
During repeated vomiting, a large amount of gastric juice can be lost, which can lead to severe dehydration 4. Some causes of persistent vomiting:
- Alcohol intoxication
- Food poisoning
- Motion sickness
- Severe nausea and vomiting during pregnancy (morning sickness, hyperemesis gravidarum)
- Certain infectious diseases (bacterial meningitis)
- Kidney stones, urinary tract infection (UTI), including kidney infection (pyelonephritis) 25, kidney failure (uremia)
- Hepatitis, acute pancreatitis, appendicitis, intestinal obstruction
- Cancer and chemotherapy
- Hypercalcemia, hyponatremia
- Cyclic vomiting syndrome
- Bulimia nervosa
6. Severe or Prolonged Diarrhea
Some causes of diarrhea 5:
6.1. Acute, Severe Diarrhea
- Excessive alcohol ingestion
- Food poisoning
- Gastroenteritis or “stomach flu,” mainly in infants and toddlers
- Cholera — water loss may exceed 1 liter per hour (more than 20 liters per day) 21.
6.2. Chronic or Recurrent Diarrhea
- Celiac disease
- Crohn’s disease
- Intestinal parasites
- Antibiotic-associated diarrhea
- Laxatives abuse
7. Excessive Urination
- Untreated diabetes type 1 12
- Kidney disease, such as polycystic kidney disease or lithium toxicity resulting in nephrogenic diabetes insipidus 14
- Hypokalemia 14
- Water pills (diuretics) 15
- Hormonal imbalance
- Pituitary tumor (adenoma) causing central diabetes insipidus 14.
- Severe acute adrenal insufficiency (adrenal crisis) in Addison’s disease 16
- Cold ambient temperatures induce excretion of the urine or “cold-induced diuresis” 8.
- Other causes of excessive urination
Burns can cause damage of the skin vessels resulting in greater water evaporation from the skin 22.
10. High Altitude
- After arriving at high altitudes (over 11,500 feet or 3,500 m), unacclimated individuals often feel less thirsty 4. They may also lose 1-2 liters of water due to increased urination, probably due to cold-induced diuresis, and may remain dehydrated for about 14 days 8,10. Additionally, dry air at high altitudes stimulates water loss through skin and breathing.
What about alcohol and caffeine?
Alcohol, caffeine 29 and foods high in protein 27,28 only mildly increase water excretion through the kidneys and by themselves do not likely cause significant dehydration 13. Check the list of appropriate beverages for dehydration.
- References +
- Merck Manuals Dehydration definition
- National Academic Press Obligatory water loss
- National Academic Press Obligatory water loss in a dehydrated person
- Patient.co.uk Repeated vomiting
- Mayo clinic Diarrhea causes
- MedlinePlus Decreased or absent thirst
- National Academic Press Decreased thirst at high altitudes
- PubMed Cold-induced diuresis
- Brattleboro Memorial Hospital Cold weather and dehydration
- National Academic Press High altitudes
- National Academic Press Water requirements in workers at heat
- Diabetes.co.uk Diabetes and polyuria
- DTIC.mil Dehydration overview
- Clinicalkey.com Diabetes insipidus
- Patient.co.uk Diuretics side effects
- Uptodate.com Adrenal insufficiency
- Hartfordmarathon.com Sweating rates in marathon runners
- National Academic Press Sweating in workers at heat
- TOXNET Amphetamine and hyperventilation syndrome
- Health.gov.au Ecstasy side effects
- CDC Cholera
- Burn-injury-resource-center.com Burns
- PubMed Central Physical effects of obsessive-compulsive disorder — OCD
- Skinsight.com Yeast infection of the mouth
- Drugs.com Acute pyelonephritis complications
- Guideline.com Risk factors for dehydration
- Nutritionandmetabolism.com Dietary protein intake and renal function
- PubMed Dietary protein intake and hydration
- PubMed Caffeine, body fluid-electrolyte balance and exercise performance