4.2 Hydration

Water is virtually everywhere, from soil moisture and ice caps to the cells inside our own bodies. Depending on factors like location, fat index, age, and sex, the average human is between 55 and 60% water. At birth, human babies are even wetter, being 75% water. They are swimmingly similar to fish, but their water composition drops to 65% by their first birthday. So, what role does water play in our bodies? And how much do we actually need to drink to stay healthy? The H2O in our bodies works to cushion and lubricate joints, regulate temperature, and to nourish the brain and spinal cord. Water isn’t only in our blood. An adult’s brain and heart are almost 3/4 water. That’s roughly equivalent to the amount of moisture in a banana. Lungs are more similar to an apple at 83%. And even seemingly dry human bones are 31% water.

If we are essentially made of water and surrounded by water, why do we still need to drink so much? Well, each day, we lose 2 to 3 litres through our sweat, urine, and bowel movements, and even just from breathing. While these functions are essential to our survival, we need to compensate for the fluid loss.

Maintaining a balanced water level is essential to avoid dehydration or overhydration, both of which can have devastating effects on overall health. At first detection of low water levels, sensory receptors in the brain’s hypothalamus signal the release of antidiuretic hormone. When it reaches the kidneys, it creates aquaporins-- special channels that enable blood to absorb and retain more water, leading to concentrated dark urine.

Increased dehydration can cause notable drops in energy, mood, skin moisture, and blood pressure, as well as signs of cognitive impairment. A dehydrated brain works harder to accomplish the same amount as a normal brain, and it even temporarily shrinks because of its lack of water. Overhydration, or hyponatremia, is usually caused by overconsumption of water in a short amount of time. Athletes are often the victims of overhydration because of complications in regulating water levels in extreme physical conditions.

Whereas the dehydrated brain amps up the production of antidiuretic hormone, the overhydrated brain slows or even stops releasing it into the blood. Sodium electrolytes in the body become diluted, causing cells to swell. In severe cases, the kidneys can’t keep up with the resulting volumes of dilute urine. Water intoxication then occurs, possibly causing headache, vomiting, and in rare instances, seizures or death. But that’s a pretty extreme situation.

On a normal day-to-day basis, maintaining a well hydrated system is easy to manage for those of us fortunate enough to have access to clean drinking water. For a long time, conventional wisdom said that we should drink eight glasses a day. That estimate has since been fine tuned.

Now, the consensus is that the amount of water we need to imbibe depends largely on our weight and environment. The recommended daily intake varies from between 2.5 to 3.7 litres of water for men and about 2 to 2.7 litres for women-- a range that is pushed up or down if we are healthy, active, old, or overheating.

While water is the healthiest hydrator, other beverages, even those with caffeine like coffee or tea, replenish fluids as well. And water within food makes up about a fifth of our daily H2O intake. Fruits and vegetables, like strawberries, cucumbers, and even broccoli, are over 90% water and can supplement liquid intake while providing valuable nutrients and fibre.

Drinking well might also have various long-term benefits. Studies have shown that optimal hydration can lower the chance of stroke, help manage diabetes, and potentially reduce the risk of certain types of cancer. No matter what, getting the right amount of liquid makes a world of difference in how you’ll feel, think, and function day to day.