Water is essential for life. Without it, we can only survive for days. The majority of our body is composed of water and adequate intake is related to our energy levels, weight maintenance, performance and overall functioning. While we know water is fundamental to our composition and survival, our current understanding of how hydration specifically affects health, well-being and chronic disease is lacking. Water requirements are largely based at a population level from retrospective studies in healthy people. In the US, we get an estimated 22% of our daily water intake from a proportion of beverages and food sources such as fruits and vegetables.
As humans, we have a sensitive system of physiological controls to maintain body water. This is mediated by the sensation of thirst. When the body is thirsty, you have already been triggered to respond from water deficiency, or dehydration. Our kidneys play a key role in regulating our fluid balance and they function best with abundant water. A concentrated or dark yellow, urine causes the kidneys to work hard, expending energy, causing wear and tear and unneeded stress on these vital organs.
Most of what we know about the benefits of water is from deficits seen in those dehydrated compared to hydrated people. Here’s a short synopsis of studied differences.
Performance: Athletes can commonly lose up from 6- 10% of their body weight from sweat loss causing dehydration. Decreases in physical performance have been seen in as little as 2% loss of hydration. This can present as reduced endurance and motivation, more fatigue with perceived increased effort. Drink water before, during and after exercise.
Cognition, aka Brain Power: Dehydration can cause changes in mood such as fatigue and irritability and cognitive functioning such as concentration, alertness, short term memory, and performance on psychomotor skills. Feeling sluggish at work or moody at times? Try adding more water and seeing if you feel different.
GI Function: Dehydration may be related to constipation and can also alter the electrolyte balance in your body. Your body can lose significant amounts of water through the GI system and even lead to death in diarrheal diseases when the body can’t re-hydrate fast enough. The small intestines can absorb up to 15 liters of water each day!
Headaches: Dehydration can lead to headaches and can trigger or prolong migraines. One randomized trial found that those who added 1.5 liters water/day to their current diet found reduced intensity and duration of their headaches. For dehydration headaches, usually drinking water will provide relief in as soon as 30 minutes. If you are prone to dehydration headaches, stay ahead of the game rather than try to catch up with headaches.
Skin: Our skin is made up of 30% water and is a crucial barrier to the outside world. Skin is important in maintaining our water levels and preventing water loss. There is not good established evidence to show that drinking water contributes to ‘glowing’ skin but it will improve skin thickness and hydration.
Chronic Disease: As water is essential for our health, it makes sense that dehydration could contribute to chronic diseases. Hydration has been associated with reduced incidences of constipation, exercise induced asthma, urinary tract infections, high blood pressure, fatal coronary heart disease, clot formation, and stroke.
Weight: Staying hydrated can help with weight loss, reduce the amount of calories consumed and reduce hunger. Many times the sensation of hunger is mistaken for thirst. You can reduce your overall energy needs by an estimated 10% when you replace sugary drinks, soda, juice, and whole milk with water. Drink water before or with each meal and in between. If you are trying to lose weight, drink a glass of water 30 minutes before you usually eat and swap out sugary juice and soda for flavored water.
Clearly staying hydrated is important. But how much should you get? There is great variability between water needs with different ages, physical activity, weight and metabolism. The Institutes of Medicine has determined an adequate intake (AI) is roughly 3 liters (~13 cups) for men and 2.2 liters (~9 cups) for women of total beverage per day. Eight 8-ounce glasses of water a day is about 1.9 liters so the common “8 by 8” rule is not too far off.
- If you exercise, add 1.5 - 2.5 cups of water for short exercise and even more if you are exercising intensely for longer than an hour.
- Add more water with hot or humid weather and high altitude.
- Pregnant women should drink 10 cups and breast-feeding woman even more with 13 cups a day.
- When you are sick with a fever, or have vomiting or diarrhea you lose more fluids than normal. Your doctor may ask you drink rehydration solutions as plain water may not replenish electrolytes you have lost.
Generally speaking, drink enough fluid that you rarely feel thirsty and your urine is colorless or light yellow. You can drink too much water, but this is uncommon in healthy adults and usually only seen in endurance athletes.