I’ve long heard the advice that you should drink eight glasses of water a day and you should not wait until you are thirsty. This is a myth that has been debunked many times. Thirst is actually an excellent indicator of when you should drink fluids. However, when you are exercising or competing in the hot sun, you should be proactive with your hydration. Related to this is the advice that you should always drink water first thing in the morning because you wake up dehydrated. If you strength train, do bodybuilding workouts, run, etc. first thing in the morning, this could be especially important.
How is Dehydration Defined?
Is this true? Are you dehydrated first thing in the morning and does this mean it is imperative that you drink a glass of water right after you get up?
Dehydration is defined by the amount of fluid loss as a percentage of body weight. Since your body is mostly water, this makes sense. If you lose a large amount of body weight in a very short time, most of it is probably fluid loss.
Mild dehydration is considered to be around 5% loss of body weight (in fluids). A 10% loss is considered moderate dehydration, and a 15% loss is considered severe.
So, do you start the day having lost 5% of your body weight in fluid while you slept? This would mean, mind you, that if you weighed 160lbs when you went to sleep you’d weight 152lbs when you woke up. Anybody who has tried to lose weight can attest that this doesn’t routinely occur. Assuming you weren’t already in a negative body water balance when you went to bed, you aren’t going to be dehydrated when you wake up.
However, you do lose fluids while you sleep. While a morning glass of water probably isn’t a bad idea for all of us, if you strength training or do other exercise in the morning, hydration should be the most important item on your pre-workout list.
You can lose around one percent of your body weight in normal overnight fluid loss due to respiration, transpiration, and urine production.
How Much Dehydration Impairs Performance?
Given that you are not considered “dehydrated” at only a 1% body weight loss, certainly, a sub-threshold of hydration exists for adequate athletic performance. Normally, this threshold is theoretically set at about 2% of body weight in fluid loss for endurance events, and about 3 to 4% for strength and power type events.
Although there are other things that impair your strength training performance first thing in the morning, dehydration, then, should be one of them. However, you must keep in mind that these thresholds are theoretical estimates only. For some, performance decrements may start creeping in at lower levels of dehydration. This will be more important for endurance training, especially in hot arid climates, than strength and power. All in all, however, drinking some water before you do your morning training is a good idea.
If you do not have to urinate first thing in the morning, or if your urine is very dark, this probably indicates at least some level of inadequate hydration.
Coffee and the Diuretic Effect
What if you just must have your coffee first thing in the morning? Isn’t caffeine diuretic? Will it dehydrate you?
If you are a habitual coffee drinker and you have been consuming caffeinated beverages in the morning for years (or a lifetime, like me), then the diuretic effect of coffee or other caffeine sources should not be of great concern to you. Coffee and tea will actually aid in hydration to some extent, although not as well as plain water or sports drinks. It is a myth that caffeinated beverages do not count toward hydration.
Deciding to skip your morning coffee because you think it may dehydrate you and impair your performance will likely backfire if you suffer from caffeine withdrawal. Trust me, a caffeine headache will be much worse for your strength training performance than a mild negative body water balance.
To be safe, if you must have coffee before you train in the morning, have some water as well. Keep in mind that you will probably have to urinate quite soon.