That life sustaining substanence ...

[Military Diver]

Doctors,


This is a two part question, one of which is more or less for our own personal amusement and the other a bit more serious.

Often you can see many divers downing their early morning pre-dive toxic mixture of choice, such as some steaming hot Coffee, Tea, Coco or maybe even (my favorite) a cold CocaCola ...

1) What possible negative side effects, if any, could this bring to divers? I have noticed on more than one occasion a couple of you doctors have gotten up on the soap box and stated that if you are taking a drug (I'm speaking about legally of course) for an effect that there is always a chance of a negative effect, especially when diving... Usually the Morning Mocha Monsters are trying to wake up still, while other are just looking to warm up (or tank up for the old wetsuit warming session once in the water) before their dive.

I was wondering if depth can have some nasty effects or possibly accelerate DCS in strained divers caused by or advanced by the infusion of Caffeine to the system? Dr Deco, has NASA done any studies on the effects these morning favorites might have?


Thanks as always for your thoughts ...

 

[BillP]

Hi Miltary Diver:

The main concern with the drinks you mention has to do with the effects of caffeine. Caffeine is a central nervous system (CNS) stimulant, a GI stimulant, and a diuretic.

Typical caffeine content of various drinks*:

Pepsi Cola 0.10mg/ml
Dr. Pepper 0.11mg/ml
Coca-Cola 0.13mg/ml
Mt. Dew 0.15mg/ml
Jolt 0.20mg/ml
Tea 0.28mg/ml
Coffee 0.71mg/ml

There is recent literature (see elsewhere on the board) about the potential risk of mixing pseudoephedrine (Sudafed)- another CNS stimulant- with diving, particularly with nitrox, due to the possible increased risk of O2 toxicity and seizures. I haven't seen anything specifically about caffeine's CNS stimulating effect and diving but I would suppose it would have the same theoretical concerns.

Caffeine stimulates acid secretion in the stomach and reduces the tone of the lower esophageal sphincter muscle between the esophagus and stomach in some people. Not a good combination when you might already be seasick.

Caffeine is a diuretic. It makes you pee. If you lose more fluid than you take in (for whatever reason), you become dehydrated. Dehydration increases the risk of DCS.

OK, now I'm gonna depart from the "conventional wisdom" about caffeine and diuresis for a minute here. I might be all wet with this, so if any of you have better info, feel free to chime in. Caffeine is indeed a diuretic. It makes you pee about 1ml of fluid per mg of caffeine. Coffee has (roughly) 0.71mg of caffeine per ml. So for every 1 ml of coffee you drink, you will pee about 3/4 ml of fluid. For an 8 oz (240ml) cup of coffee, you will pee an extra 170-180ml of fluid. So you're still 60-70ml of fluid ahead. If you drink coffee instead of water you will not be as well hydrated, and if you start off dehydrated (as many divers are on multi-day trips) you will be less likely to rehydrate effectively if you drink coffee instead of water. But if you drink coffee in addition to the water you would normally drink on a dive trip to maintain your hydration, the coffee won't dehydrate you. (Can you tell that I'm a coffee drinker? Some day I'll give you my thoughts on salt and cholesterol. ;-)

Let me know if you think my numbers are wrong or my thinking flawed.

Bill

(*These numbers will vary by method of preparation for tea and coffee, and by country for the sodas.)

 

[Ladydiver]

Hi BillP,

I knew that Caffine acted as a diuretic, but I did not realize just how much fluid a person expelled per mg of consumption.

I know of a couple of people who drink nothing but coffee for the first 3/4's of the day, everyday. Now I can better explain to them why that is not a good thing as far as diving is concerned and as far as general fluid intake is concerned.

Thanks for the info!

Cheers,

 

[turnerjd]

BillP

Isn't this a balance between water in / water out?

Surely we lose a fair ammount of water through perspiration, so surely IF we drink coffee only we are in a positive water balance if: sweat < (total vol. drunk - vol. caffeine causes up to pee out)?????

Then, we are in H2O deficit if: sweat > (total vol. drunk - vol. cafeine causes up to pee out)

So, in hot countries you need to drink more water with your coffee, whereas me here in nice cold europe, I can get away with just 4 or 5 cups of coffee as it never gets hot enough to work up a sweat.

That is one way of rationalising why I dive in the (cold) UK!

Jon T

 

[BillP]

If you lose more fluid than you take in (for whatever reason), you become dehydrated.

Hi Jon:

Yes, it is a balance of water in vs. water out. There are several ways you lose water. Through sweat, evaporation from the skin without sweating, through the lungs (particularly when breathing dry scuba air), loss in the stool, etc. When you're traveling and exerting yourself, like on a scuba trip, you need to increase your fluid intake.

The point I was trying to make about caffeine is maybe the Great Taboo that some people seem to have concerning coffee and diving is perhaps over stated. Caffeine isn't such a diuretic that drinking a cup of coffee with breakfast or a Coke with lunch is going to undo all the water drinking you've done. You still need to drink the water, but I don't think that you're a terrible person if you have a cup of tea too.

Bill

 

[turnerjd]

BillP,

Do you have figures for how much you lose by the other routes, so that I can have a scientifically calculated safe dose of caffeine in the morning?

I would like to be able to prove to people that my normal 4 cups of coffee in the morning isn't too bad!!

Jon T

 

[Dr Deco]

Dear Military Diver and Readers:

BillP has the right story on diuretics as far as I am aware. It is basically water in versus water out. If the coffee is diluted, or water drank in addition, you are probably OK on the hydration issue. You are in trouble when you are so dehydrated that your tissue perfusion is negatively influenced. (Dr. Lee Somers, diving officer for the University of Michigan, once wrote a short piece entitled "If You Can’t Spit, Don’t Dive.")

NASA has not performed any studies on coffee or any other diuretic as this is not a consideration in either NASA research or extravehicular activity (EVA). Virtually all of our research and development work involves depressurization lasting three to six hours in the altitude chamber. Test subjects are instructed to be hydrated but not to drink diuretics because of the logistics of bathroom breaks in the chamber itself. Thus, most subjects are careful to limit their caffeine intake to save themselves problems a few hours down the line.

Astronauts performing EVA are instructed to remain well hydrated during the duration of the work. For this, they have a large drink bag in the suit itself that is accessible to the astronaut by a plastic drinking tube. They are told that this bag (about a quart) should be empty by the time they return to the space craft. This has never been a problem. [The other side of the equation is handled with a very large diaper.]

Dr Deco

 

[BillP]

Hi Jon:

I can't give you an exact number on the amount of daily fluid loss. It's just too variable depending on weather, activity, personal physiology etc. A good rule of thumb is to drink an extra two quarts of fluid per day when you're diving. More if it's hot, you have a touch of traveler's diarrhea, etc.

There is another problem with drinking caffeine. One measure of whether you're drinking enough fluid is if you're urinating. If you drink caffeine you will still urinate even if you're not as well hydrated and you could be fooled into thinking you're well hydrated when you're not. So you need to be extra vigilant about drinking plenty of other fluids when you've had caffeine.

Mind you, I'm not recommending caffeine, I just don't think it needs to be demonized to the degree some have taken it.

Bill

 

[turnerjd]

BillP,

I agree that it isn't as bad as everyone says, I am just a trifle fed up of people with a holier-than-thou attitude telling me not to drink caffeine in the morning before diving.

As a general rule, people need to keep away from me until I have at least 2, possibly three coffees inside me in the morning.

For me, the disadvantage of not having that coffee in the morning, is greather (IMNVHO) than the disadvantage of drinking it (provided I am relatively hydrated).

This is a situation that can only get worse living in france, because they have never heard of filter coffee here. Everything is about 10 times strength, almost equal to an expresso.

such is life!!

Jon T

 

[Mario S Caner]

Regarding urination: I have always been told that when you are diving, if you aren't peeing in between dives and when you do pee, if it isn't colorless, you aren't intaking enough water. Would you agree that this is accurate?