Hydration

Water, water everywhere, but not a drop to drink? Well, you’d better have a solution to that problem, because hydration can play a key role in a diver’s health and safety.

Most divers have heard the “dehydration is bad” lecture, and some are even familiar with how a lack of proper hydration can play a part in dive injuries like decompression illness (DCI). But few take the time to learn the finer points of hydration and truly understand why it is so important. Since it plays a significant role in many calls answered by DAN, we thought we’d take a look at it so divers understand why they hear so much about it.

What does “hydrated” mean?
When you talk about “hydration,” you’re really talking about the level of fluid within a person’s body. “Fluid” can refer to blood, water, or other liquids found within the system, but regardless, fluids are necessary to the human body, as they affect nearly every metabolic process. However, simply having fluids in your body is not enough – hydration is all about finding the proper balance of fluids. Too much or too little, and your body’s ability to function properly becomes compromised.


How do you get “dehydrated”?
“Dehydration,” by definition, simply means a lack of balance in the body’s fluids. Specifically, it refers to a negative balance, or too few fluids, as opposed to having a fluid surplus. The balance of fluid is maintained by a complex process of hormones and electrolytes, and it doesn’t take much to throw it off. You might be surprised by how many elements of diving play a part:

Physiology and Central Fluid Loss
When a body is immersed in water, the blood vessels narrow, or constrict, and lose ability to carry a full volume of blood around the body. In response, the volume is concentrated is specific areas, namely the heart, lungs, and core vessels throughout the body.

As these shifts occur, the changing volume is measured and tracked by an antidiuretic hormone that regulates the body’s urine output. Sensors in the neck monitor the volume of blood in the major vessels, and when the sensors pick up the increased volume of blood in response to immersion in water, they send the antidiuretic hormone into action. The hormone reacts to the increased blood volume by shutting off, which in turn sends the kidneys into overdrive making urine. The increased urine output, called a central fluid loss, continues as long as the blood volume remains increased and concentrated.

Lungs
Believe it or not, another major source of hydration depletion for divers comes from the lungs. One of the lesser-known functions of the lungs is to heat and humidify the air we breathe. When we breathe compressed air, the lungs have to increase their efforts to compensate for the dryness of the air. Even on a dive as short as thirty minutes, up to a cup of moisture can be lost from the lungs alone. This also falls under the category of central fluid loss.

Cheers
Of course, everyone knows that drinking and diving don’t mix, but do you know why?

Alcohol contains high levels of sugar, levels higher than are normally found in the body. When those higher levels are present, the blood and other fluids have to work harder to move around and dilute them. Alcohol also serves as a trigger for the antidiuretic hormone; when alcohol in any form is present in the body, the hormone is turned off and the increased urine output begins.

The same can be said for caffeinated and high-sugar drinks, as they, too, turn off the antidiuretic hormone. So if you’re trying to hydrate with soda, coffee, high-energy drinks or beer, you are actually not making the best choice, as these are not optimal fluid sources.


Et Cetera
Don’t forget about the miscellaneous factors that can add up to problems for your hydration levels, either. If you’re diving in the summer months or in a tropical climate, sweating can significantly contribute to dehydration. If you find the sea getting the better of you, remember that every time you “feed the fish,” you’re depleting your body of valuable fluids. The same holds true if foreign water triggers a case of “Montezuma’s Revenge.” Any easy rule of thumb is this – every time your body loses fluids (by whatever method), those fluids need to be replaced. This is especially true when those fluids are lost quickly or in large quantities.


How do you stay hydrated?
One of the keys to staying hydrated is to remember that it is a cumulative process. Contrary to popular belief, dehydration does not happen overnight, nor does rehydration of the body happen with a glass of water.

As we said earlier, the best rule of thumb to maintain hydration is to replace fluids as they deplete. This means drinking water regularly as you sweat (or otherwise lose fluids), refraining from drinking or, if you can’t do that, at least supplementing alcoholic beverages with water. If you’re actually in the situation of rehydrating, you’ll need to drink more than you normally would, as you’ll have not only to maintain, but replace the fluid you lost. Think of having to rehydrate as repaying the loan and the interest.

Water is the best fluid you can drink to stay hydrated; if you’re in an unfamiliar environment, try to stick to bottled or filtered water. If you like a little more flavor in your beverage, you can also try a low glucose, balanced electrolyte sport drink. Minimize consumption of alcoholic, caffeinated, and high-sugar beverages.

A little known fact—eating is a part of hydration. Drinking water without consuming any salt can lead to hyponatremia, a state of diminished electrolyte levels. It’s a relative state; your goal is to have electrolytes sufficient for the amount of fluid in your system. Just like too little fluid creates an imbalance, so, too, can a surplus. Extremely high fluid levels can dilute electrolytes and actually impair the hydration of cells. Salty snacks like peanuts or pretzels can be a great way to maintain electrolyte levels. It’s important to note that hyponatremia is a relatively rare condition, so don’t shy away from drinking water in fear of it. Remember, hydration is all about balance – have a snack while you replenish those fluids, and your body will get what it needs.

What Does It Mean for Divers?

For divers, all of this means incorporating hydration into your dive plan. Because hydration is a state easily depleted (and not quickly reachieved), increase your drink intake several days before you dive. Or, instead of increasing your fluid intake, at least adjust the intake so that the amount of coffee, alcohol and sugar is decreased.

On the day of your dive, remember to drink water early and often. It’s better to drink steadily and constantly throughout the day than to try and consume a liter of water once or twice throughout the day (although even that is better than drinking nothing at all).

If you find yourself feeling thirsty, increase your fluid intake a bit, as thirst is a signal of dehydration.

And for divers, it’s also about remembering why proper hydration is so important. There is a lot of talk about dehydration and decompression illness, and while dehydration alone is not often a trigger for DCI, it can certainly be a contributing factor. Remember, hydration is all about maintaining the body’s ability to execute its metabolic processes, and when that ability is compromised, those processes suffer. So if you dehydrate yourself and compromise your body’s ability to execute its metabolic processes, you’re compromising its ability to off-gas the nitrogen your system absorbed on the dive.

Staying hydrated really can directly impact your health and safety while diving, so make hydration a constant – and important – part of your dive plan.