The dehydrating effects of caffeine and alcohol have commonly been advanced by a myriad of authorities, including Harvard Medical School and Vanderbilt University. But recent studies call in question whether drinks containing caffeine decrease hydration like alcohol does. The effects of caffeine and alcohol on hydration can no longer be lumped together.
Caffeine and Hydration
Mixing water, caffeinated and non-caffeinated drinks causes no significant differences in water saturation levels. A 2000 study at the University of Nebraska Medical Center compared hydration levels when participants drank varying amounts of water, caffeinated and non-caffeinated drinks. Researchers concluded there was no difference in the hydration levels of those who took in similar amounts of liquids in a variety of caffeinated and non-caffeinated forms.
Caffeine and Exercise
Substituting caffeinated drinks for water or non-caffeinated drinks cause no hydration difference in sports performance or activity levels. A 2005 study at the University of Connecticut, Human Performance Laboratory showed no differences in fluid-electrolyte balance and renal function for adult males participating in the study. The researchers concluded that the general belief that caffeine forms a diuretic leading to accelerated dehydration wasn't supported by the evidence.
Alcohol and Dehydration
In contrast to studies on caffeine and dehydration, alcohol tends to dehydrate the body as a diuretic. When athletes exercise and re-hydrate with varying amounts of alcohol in their drinks, Peak Performance reported the amount of water lost in urination was in direct correlation to the percentage of alcohol contained in the drink. Simply put, the more alcohol content in the drink, the less water content the athlete was able to maintain.
Alcohol as a Diuretic
Drinking alcohol directly acts on the body to lose water through urination. Alcohol lessens the amount of the antidiuretic hormone which acts on your kidneys called vasopressin. Instead of water and salt being reabsorbed into the body, water is excreted through urination which can then push your body towards dehydration. The water loss from alcohol induced dehydration also causes a loss of needed nutrients and minerals such as magnesium, potassium, calcium and zinc according to Peak Performance.
