Avicenna's View on Optimal Daily Water Intake.

Background: Fluid intake is an essential factor in having a normal homeostasis. However, proper amount of daily water intake in a healthy individual is controversial. There is a prevalent thought that we all have to drink eight glasses of water daily, however, it lacks enough supportive evidence at least for healthy individuals. Here, we try to clarify this topic from the perspective of Avicenna and traditional Persian medicine (TPM).

Methods: The most important traditional Persian medical encyclopedia, Al-Qanun fil-Tibb (Canon of Medicine), was reviewed. Furthermore, Medline, EMBASE, Scopus, IranMedex, and Science Iranian Database (SID) focusing on the keywords "traditional medicine", "water intake", "fluid'', and "complementary and alternative medicine" were reviewed to find relevant information.

Results: Avicenna believed that the demand for daily water is not the same in different individuals. The determinant variables mentioned in his book, The Canon of Medicine, comprises mizaj (temperament), health status, age, sex, season, place, habits, occupation, etc. He believed that water in extra amount quenches the hararat-e-ghariezi, which is the basal internal heat to convey normal homeostasis and metabolism in the body.

Conclusion: Several factors determine the actual need of any person to drink water. Consequently, recommending a specific amount of daily water intake for all is illogical. Moreover, important recommendations of TPM sages on an appropriate amount of water intake should be considered to prevent associated disorders.