This post was inspired by a recent vist my girlfriend, kelsey, had to the optometrist. During the appointment the optometrist mentioned to kelsey that her eyes seemed to be unusually irritated and slightly dry. Kelsey told the doc that she didn't know why her eyes seemed to be dry because she felt like she was consuming adequate amounts of fluid. This is where the optometrist decided to spend the next 5 to 10mins discussing hydration. He told Kelsey that people tend to become more dehydrated in the winter due to the fact that most individuals development an aversion toward cold drinks replacing these with coffee or tea. He stated that drinking coffee or tea on a regular basis leads to dehydration. More specifically he estimated that for every cup of coffee you drink you need to consume an extra 8-12 oz of water during the day (how he determined this is beyond me).

To say the least I was a bit flustered when Kelsey relayed this conversation to me. To be more specific I felt like stabbing myself in the eye with a dull butter knife. I mean it was by no means the first time I have heard this stated by a medical professional. In high school this was something I heard on a regular basis from my athletic trainer and coaches. I've also heard the same statement from a few different M.D.'s.

But where did they get this fact? Coffee/Caffeine dehydrates you? Really?

Contrary to what most of the public believes and accepts and to what medical professionals desire you to believe preach, the science supports the opposite.

First Mr. Optometrist let me begin by offering another possibility for why Kelsey's eyes are dryer in the winter. Could it be because almost every place she spends her time in has the heat jacked up to 72 degrees. The way central heat works it causes moisture to be quickly removed from the air resulting in the dehumidifying of living spaces. I would highly recommend buying a humidifier to place in your bedroom or living room to offset the effects of the heater. I means I don't expect you to turn the heat off and freeze to death (or do I).

Second why are you perpetuating an unsupported claim that you probably read on CNN in your spare time. This is a common practice I think among medical professionals. They abuse the trust and respect people have for them due to the letters after their names speaking about topics they are not fully versed in or have done little investigation into. This is wrong and irresponsible. It contributes to the already overwhelming amount of misinformation that exists in the world.

Now to get to the real issue, "Does consuming coffee/caffeine dehydrate you?".

NOOOO!!!!!!!!! Oh, whats that you didn't hear me? Well let me say it again.

NO CONSUMING COFFEE DOES NOT RESULT IN DEHYDRATION!!!!

A review of ten studies found that consuming up to 550mg of caffeine per day does not cause fluid-electrolyte imbalances in athletes and fitness enthusiasts. This means to important things first if caffeine consumption doesn't affect hydration levels in athletes and fitness enthusiasts, which are by nature more at risk to dehydration due to the amount of extra fluid lost in sweat each day, then it should in way have any adverse affects on general population people. Second it means that you would have to drink more than 24 to 38 ounces of coffee each day to even reach the upper limits of the caffeine amount tested in this study considering that an average cup of coffee contains between 60 to 100 milligrams of caffeine.

Another review done the following year looked at whether or not drinking caffeine containing beverages results in negative fluid consumption. Meaning does the fluid expelled outweighed the fluid consumed. They found that this was also not the case. Which indicates that drinking coffee can not directly dehydrate you.

Let me finish by saying that coffee should not be constitute your only fluid consumption all day. To be well rounded and healthy you do need to consume adequate amounts of H2O. But it will never hurt you to have a few 4 ounce cups of coffee each day if you choose to. In fact their has been numerous studies demonstrating that consuming coffee, specifically caffeine in moderate doses can have positive effects ranging from reduction of risk of death  from CVD to protection from parkinson's disease.

So go ahead and drink that morning cup of coffee! While you at it have a couple second helpings to go along! Try to use healthy taste modifiers, such as honey, agave nectar, or a bit of low-fat milk.

DRINK UP!!!

References

Armstrong LE. Caffeine, body fluid-electrolyte balance, and exercise performance. Int J Sport Nutr Exer Metab. 2002 Jun;12(2):189-206.

Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a reviewJ Hum Nutr Diet. 2003 16(6):411–420.

Koizumi A, Mineharu Y, Wada Y, Iso H et al. Coffee, green tea, black tea and oolong tea consumption and risk of mortality from cardiovascular disease in Japanese men and women. Journal of Epidemiology and Community Health 2011 65: 230-240.

Webster Ross G, et al. Association of Coffee and Caffeine Intake With the Risk of Parkinson Disease.  JAMA. May 24, 2000, 283:20