Does Coffee = Dehydration?

Do Dehydration and Coffee Consumption Go Hand-in-Hand?  Let's Pray Not!!!!!!!

I don't have an exact figure, but suffice it to say that on a scale of 1-10, I LOVE COFFEE!  However, if you're a fellow coffee aficionado, you've likely heard word from naysayers that coffee, and more so caffeine, consumption can lead to dehydration.  In fact, both my freshman and sophomore years of college, when I took gen. ed. health courses, my professors espoused that for every cup of coffee you drink, you ought to consume an equal amount of water.  But is this so?

After taking a look at the actual published research, I can happily say that we have little to fear!

The Study - No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population

Research published this January for PLUS One, by authors Killer et al., suggests that - "coffee, when consumed in moderation by caffeine habituated males contributes to daily fluid requirement and does not pose a detrimental effect to fluid balance."  The authors took 50 male habitual coffee drinkers (pay attention to the habitual part, it's important!), and assigned them to one of two groups:  one group drinking "4×200 mL of coffee containing 4 mg/kg caffeine," and the other group drinking an equal amount of water.  The study lasted for a total of 3 days.

While the authors compiled various data tables, the table you see below most interested me - 

This data consists of total body water (TBW), as measured by deuterium oxide analysis.  Pre-Trial measurements were taken at Day 1, and Post Trial measurements were taken at Day 3.  As you can see from the above data, the coffee group didn't experience any loss of water weight.  In fact, the coffee group actually experienced an increase in water weight (though this increase is negligible).  Very interesting news for anyone so enamored by the vivacious claims of supposed "experts" who would have use believe that coffee has just the opposite effect of that reported by Killer et al.  Coffee does not lead to dehydration.  Moreover, it can actually prevent dehydration; like plain water itself, only in better fashion because, well, it's coffee! 

The Importance of Habituation

One thing you ought to keep in mind as you consider this information is that this data may really only hold true for habitual coffee/caffeine drinkers.  Take a look at this table the authors include in their report -

Effect of caffeine consumption on urine production.

Authors	Caffeine Dose(mg)	Caffeine Source	Test population	Diuretic Effect
[8]	4 mg/d (200–700 mg)	Caffeine tablet	Habituated caffeine users	Yes –during first day only
[9]	490–680 (8.7 mg/kg bw)	Caffeine powder added to carbohydrate electrolyte drink Vs carbohydrate electrolyte drink	Caffeine naïve (Habitual coffee drinkers – 4 day pre-trial deprivation)	Yes
[10]	642	Caffeinated coffee	Caffeine naïve (Habitual coffee drinkers – 5 day pre-trial deprivation)	Yes
[14]	452	Caffeine tablet	Habitual caffeine users – 98±17 mg/day	No
[17]	360	Caffeine tablet	NA	Yes
[15]	300	Caffeine tablet	Habitual coffee drinkers – 8 h pre-trial deprivation	No
[25]	250	Caffeine beverage	Caffeine naïve (Non-coffee drinkers – 3 week caffeine deprived)	Yes
[31]	250	Caffeine tablet	Caffeine naïve (1 week caffeine deprived)	Yes –during first hour only
[32]	240	Caffeine beverage	Caffeine habituated users	Yes
[14]	226	Caffeine capsules	Habitual caffeine users – 98±17 mg/day	No
[16]	168 and 252	Caffeinated tea	Caffeine users – 12 h deprived	No
[13]	114–253	Caffeinated carbonated cola, Caffeinated carbonated, non-caloric cola, Instant coffee	Caffeine habituated (61–464 mg/day)	No
[17]	45, 90 and 180	Caffeine tablet	NA	No

Regarding this information, the authors state -

These studies report observations across a range of caffeine forms and doses on various markers of hydration status in either caffeine-habituated or caffeine-naive populations (individuals who do not habitually consume caffeine, or those who have abstained from caffeine consumption for ≥4 days). Although the data are somewhat varied, the general trend is that higher doses of caffeine in caffeine-naive individuals will elicit an acute increase in urine volume, yet a low to moderate dose of caffeine does not induce a diuretic effect.

In other words, those unaccustomed to caffeine consumption may experience some diuretic/dehydrating effects from relatively high doses of the substance.  Though, one notable limit of the above data befalls us:  Caffeine does not equate, 1 for 1, to coffee.  The authors rightly indicate that -

Coffee is comprised of many bioactive compounds in addition to caffeine. These active compounds may interact with each other and therefore coffee consumption cannot be directly compared to caffeine consumption in its purest form. 

Because of this very real distinction that exists between straight caffeine intake, and the consumption of coffee, I love that Killer et al. actually use coffee in their study; thus making their results a little more relevant to coffee drinkers, such as myself.

In Conclusion

If you're a regular coffee drinker, having already become well adjusted to the effects of caffeine, you have no major impetus preventing you from continuing in your coffee-love.  For those uninitiated, take time to adapt prior to diving head first into a pool full of this life-giving nectar.  In the long term, you have nothing to fear; no threat of dehydration or any other boogeymen will likely come your way.  Of course, never regard what I say here as ultimate truth.  If you think you do experience dehydration, listen to your body, not me.  I say, however, coffee lovers, drink away!