Drinking a litre of water a day has become one of the widest known of wellness ideas. I have friends who stick to the advice, and who have from time to time encouraged me to do the same. So I read with interest an article reporting a reputable international research study which concludes that drinking eight glasses of water a day may be excessive for most people.
Excessive for what?
Excessive for what? Turns out even that question is not straightforward. Perhaps the simplest answer is to avoid dehydration when the body has increasing trouble functioning normally which becomes difficult to reverse without medical intervention.
So a rule of thumb has emerged to keep us sufficiently hydrated. Heat and vigorous exercise are obvious examples of conditions speeding up dehydration. Unsurprisingly, personal factors also play a part.
The study attempts to identify the various contributing factors, to improve on that rule of thumb ‘drink plenty of water’. According to the researchers:
‘Water is essential for survival, but one in three individuals worldwide (2.2 billion people) lacks access to safe drinking water. Water intake requirements largely reflect water turnover (WT), the water used by the body each day. We investigated the determinants of human WT in 5604 people from the ages of 8 days to 96 years from 23 countries using isotope-tracking (2H) methods. Age, body size, and composition were significantly associated with WT, as were physical activity, athletic status, pregnancy, socioeconomic status, and environmental characteristics (latitude, altitude, air temperature, and humidity). People who lived in countries with a low human development index (HDI) had higher WT than people in high-HDI countries’
The Guardian interviewed Professor Yamada one the lead researchers. “The current recommendation is not supported scientifically at all,” he said, “Most of the scientists are not sure where this recommendation came from.”
More may not be better
Remember that other rule of thumb about having three a day portions of veg and fruit? That was adjusted upward to five a day.
The water rule of thumb is rather easier to manage. For most people, a litre a day is almost certainly more than enough, and anyone hoping that ‘more means better’ is probably mistaken,