One of the urban myths is that we should drink at least 5 litres of water a day if we want to stay healthy. There is no evidence to support this claim at least in healthy people who consume healthy diets. Indeed, unless we have a medical condition, for instance a high fever or a psychiatric disease, we should just drink when we are thirsty.
A study published in the prestigious journal Proceedings of the National Academy of Sciences has demonstrated that our brain is perfectly capable of judging when we are dehydrated and how much we should drink. Indeed, the drive to drink is carefully regulated, as both under-drinking or over-drinking can cause harmful health effects.
In healthy humans, brain areas controlling our emotions are activated when we drink in response to feeling thirsty, but immediately after thirst has been satisfied, other brain regions (in particular, those involved in controlling and coordinating movement) kick in to halt the drinking response.
Fascinatingly, the fluid volume consumed approximates the fluid deficit, suggesting
these brain circuits are important to prevent people from drinking too much water, which could dangerously lower blood sodium concentrations and trigger brain swelling. This study also showed that drinking to satisfy thirst was perceived as a pleasant sensation, while drinking excessive amount of water was felt as an unpleasant emotion.
Moreover, as I have previously explained, consuming a wide range of foods, multiple times a day, that are rich in water, potassium, magnesium and fibre (e.g. vegetables, fruits, whole grains, beans, and nuts), while minimizing the consumption of ultra-processed food rich in hidden salt, is key to promoting healthy hydration levels.