What amount of water do we expel through our lungs during eight hours of sleep?

From the Guidelines

During eight hours of sleep, an individual expels approximately 200-300 milliliters of water through their lungs, as supported by the general understanding of insensible water loss from the skin and lungs, which is an energy costly process consuming a quarter of the overall caloric expenditure, 0.5 kcal per 1 ml of water lost 1.

Factors Influencing Water Loss

• The amount of water lost through respiration can vary based on several factors including:
  • Humidity of the room, with drier air increasing water loss
  • Breathing rate
  • Body size
  • Individual metabolism
• These factors can influence the rate at which moisture from the lungs evaporates and is expelled from the body.

Clinical Considerations

• Water requirements parallel energy needs, with 1 kcal per 1 ml water, as generally accepted in clinical practice 1.
• However, specific clinical situations such as fever, hyperventilation, hypermetabolism, and gastrointestinal losses can increase water requirements, while conditions like renal failure and congestive heart failure may decrease them.
• The guideline for calculating maintenance water needs, such as the formula provided by Holliday and Segar in 1957, can serve as a basis but may need adjustment based on individual patient conditions.

Implications for Daily Fluid Needs

• The water lost through respiration during sleep contributes to the body's daily fluid needs.
• This is one reason why individuals may wake up feeling slightly dehydrated, especially in dry environments or when breathing through the mouth.
• Understanding and accounting for this insensible water loss can help in managing hydration, particularly in clinical settings where fluid balance is critical.

From the Research

Water Loss Through Lungs

• The amount of water lost through lungs during breathing can be estimated using the Antoine equation and the ideal gas law, taking into account air temperature, humidity, and minute ventilation 2.
• At rest, the amount of exhaled water is approximately 60-70 ml/h at a heart rate of 140 bpm, and this amount increases with physical exercise 2.
• The effect of external temperature and humidity on water lost via lungs has also been assessed, with a loss of 7 ml/h at 35°C and 75% humidity, and an increase to 20 ml/h at -10°C and 25% humidity 2.

Water Loss During Sleep

• Assuming an average resting heart rate and normal environmental conditions, the amount of water lost through lungs during 8 hours of sleep can be estimated to be around 56-112 ml (based on 7-14 ml/h) 2.
• However, this is a rough estimate and may vary depending on individual factors such as sleep quality, room temperature, and humidity.

Daily Water Balance

• The regulation of water balance is essential for maintaining health and life, and both water intake and water losses are controlled to reach water balance 3.
• Healthy adults regulate water balance with precision, but young infants and elderly people are at greater risk of dehydration 3.
• The amount of water lost through lungs is a small fraction of the total daily water loss, which also includes losses through urine, sweat, and feces 3.