You have always been told that you should drink at least two liters of water a day. It sounds good to you in the summer in hot weather, but you always struggled more in the winter. As the Guardian reports, new research conducted in Japan on a large sample of individuals has shown that perhaps this is not quite the case and that our requirements may be lower and, more importantly, that they vary from person to person.
The study bears the signature of Yosuke Yamada of Japan’s National Institute of Biomedical Innovation, Health and Nutrition and is based on an analysis of the behaviors of 5,604 people between 8 days (of age) and 96 years. The assumption from which he started was a hunch, namely that the recommendation to drink at least 2 liters a day did not consider water contained in food. In fact, normally we do not associate what we eat with the corresponding water intake, which can be instead significant: eating meat, fish, fruits and vegetables can in fact cover 50 percent of daily requirements. It is clear that, similarly, there are also foods that do not contribute much water, such as bread or eggs.
How was the research conducted? The water administered to the candidates was fortified with a stable isotope of the element deuterium, which is harmless to the human body. The elimination of deuterium from the body was taken as an indication of the degree of water absorption from the body itself. The results confirmed that as simple and effective as the “Two liters of water a day” formula is, it does little to accommodate the variability of situations and body types.
We are different
Such a conclusion is perhaps surprising, at least until you think about how many variables there can be in such a context: weight, age, physical activity level, gender, and living environment. To think that everyone needs the same amount of water per day is therefore a bit simplistic.
Those who live in warmer places or at high altitudes, as well as those who play sports or pregnant women need to take in more water. The conclusion is that the greater the energy expenditure (in playing sports or keeping functional a body fatigued by heat loss from extreme environmental conditions, for example), the greater the need to replenish fluids. How much? Men between the ages of 20 and 35 may need up to 4.2 liters a day (3.3 liters for women between the ages of 20 and 40), while a 90-year-old person may only need 2.5 liters.
Haven’t you suddenly become thirsty?