Dear Dr. Mo: How much water do I really need to stay hydrated and healthy?
Dear reader: This is the time of year where common colds are indeed common and when you will often hear that advice to drink lots of fluid, usually herbal teas or water. Of course, water is essential to your health but the needs for water vary from person to person and many factors may influence that, like for example your health condition, your daily activities, where you live, your age, metabolic rate etc.
Water is our main constituent – it makes up about 60% of our body mass. We need water to maintain normal functions: we throw out waste matter dissolved in water, water participates in digestion of food, it carries nutrients to cells, we use water to show emotions when we cry etc.
Water also helps to regulate body temperature through perspiration (sweating).
When water is insufficient we dehydrate. Dehydration is a state in which our cells don’t have enough water to function normally. Even a mild dehydration could cause fatigue because when tissues lose water, enzymes are slowing down their functions and energy production drops.
A simple way to see the link between health and water is to observe what happens when we age. As we age, the water content of our bodies is decreasing steadily and while a newborn is 80% water, in an adult this ratio is at 60% and it keeps on decreasing as years go by.
Good digestion is important for good health and water is absolutely necessary for digestive juices. In a state of dehydration, these juices are in short supply and digestion is becoming difficult. Dehydrated person may also become constipated as large intestine extracts more water to compensate for water shortage and bowl movement becomes dryer and harder to pass.
How much water do we need?
Water is constantly being lost and requires constant replenishment. We lose it in processes we don’t even think about such as breathing and digestion and we lose it in more familiar ways like urination, sweating, runny nose during colds, crying, sneezing etc.
We can replenish water with fluids and food.
For a healthy adult living in a moderate climate, daily water intake for a male would be around 3 liters and for a female around 2.2 liters. This takes into account all the fluids, everything we drink and eat in 24 hours.
Everything counts toward your total daily fluid intake: coffee, teas, sodas and alike. Until recently, we believed that such beverages had a diuretic effect (make you lose water through more urin), which in turn would mean an increased risk for dehydration. Today we know that diuretic effects of caffeine found in all such beverages are strong enough only in larger quantities of around 500 – 600 mg per day (equivalent to 6 – 7 cups of coffee).
I would always recommend drinking water instead because coffee and teas could make you nervous and sodas pack a lot of sugar.
To get your bearings on caffeine intake and if you are reaching the 500 mg threshold at which I would recommend a cut back, here are some values for comparison:
A cup of black tea contains 15 – 60 mg, a cup of green tea contains 25 – 40 mg, one espresso has 40 – 75 mg and 0.33 ml Coke has 30 – 35 mg.
Your food is also an important water source – don’t forget that! On average, food contributes with up to 20% to your daily need for water. Fruits and vegetables are rich in water (i.e. watermelon and tomato are 90% water).
When we are dehydrated, we increase the amount of food we eat (our appetite intensifies) to try to compensate for decreased fluid intake – we are often completely unaware of this change. This means that dehydration could contribute to weight gain.
8 glasses as a rule?
8 glasses of water a day is an advice that comes from many, but is it true?
There are no specific evidence to support this particular number of glasses of water as daily requirement because remember, your needs are specific to your health, activities, climate, age, sex etc. I would rather say that 8 glasses should be your minimum daily intake of fluid, not just water but all fluid combined. 8 glasses is about 1.9 liters so it is anyway close to a recommended dose.
Factors that count
Remember that we all have different bodies and needs and that our water requirements are determined by our activities, climate, season, health, age, sex, food, weight etc. Pregnant or nursing women will have increased needs for fluids.
Environment: Hot, humid weather causes sweating, which increases the need for fluid. During the winter, indoor heating dries our skin. Also, in winter times we are not as thirsty and we perspire less so it is not uncommon to forget to drink water. Appetite increases during the winter and more water is needed for normal digestion.
Physical activities: Work out or any other activity during which we break sweat increases the need for water. Additional 400 – 600 ml (1.5 – 2.5 glasses) would be enough for a shorter exercise but for longer and/or more intensive activities, more water is needed. Do not wait to get thirsty but rather take water preemptively during the activity and if it is an especially demanding and difficult activity, continue drinking water after the activity as well.
Your health: If you’re running a high fever, if you vomit, have diarrhea, you are losing increased amounts of water and you must replenish it. Take smaller amounts but do it often (i.e. a few teaspoons of water every 5-10 minutes to avoid further irritation to the stomach). In cases of more severe vomiting or prolonged diarrhea, you may need to replenish lost minerals as well so call or visit your doctor.
In cases of urinary infections or kidney stones, it is advisable to step up the water intake and your doctor will certainly mention this.
Pregnancy and breast feeding: These conditions require more water! Pregnant women should on average take in 2.3 liters of fluid daily while the nursing ones require as much as 3.1 liter.
Not every health condition warrants for more water!
Some heart diseases, certain kidney and liver diseases as well as come diseases of adrenal glands require strict control of fluid intake and even a decrease because in such cases water excretion is impaired and could be decreased resulting in (dangerous) water retention.
In principle, if you drink enough fluids that you are seldom thirsty and if you urinate about 1.5 liter or more of clear light yellow urine, your fluid intake is probably OK.
Dehydration should be prevented rather than corrected. Be especially aware of this during the winter when thirst and sweating are absent but water loss is not.
Make water your beverage of choice – it has zero calories and it is one of the most vital substances for good health and clear mind.
Yours in health,