Effects of Caffeine at High Altitude
Visitors travelling to high altitude destinations have been known to avoid coffee/caffeine intake in order to avoid the dreaded symptoms of acute mountain sickness. The theory is that caffeine leads to dehydration, which then predisposes the individual to acute mountain sickness. A few symptoms of dehydration include headache, lethargy, confusion, weakness and nausea and vomiting. Similarly, symptoms of acute mountain sickness include fatigue, headache, nausea, vomiting, shortness of breath and difficulty sleeping. Although the symptoms of dehydration and acute mountain sickness are very similar, there is no evidence to support this claim that dehydration predisposes an individual to acute mountain sickness.1 Thus, the diuretic effect of coffee and caffeine are often exaggerated. Individuals that are accustomed to drinking 12 oz. of coffee rarely suffer from the diuretic effect of the beverage.1 (See Table 1).
Table 1. Caffeine content (mg) per serving in various foods, drinks and medications.
The condition of acute mountain sickness is a response to hypoxia in the brain’s vascular circulation that causes an increase in the release of a neurotransmitter called adenosine. Adenosine binds to adenosine receptors found on the inner lining of cerebral blood vessels, causing vasodilation of the blood vessels in an attempt to increase the flow of oxygen and nutrient rich blood to the brain. This increase in cerebral blood flow, however, is painful and causes many of the above-mentioned symptoms of acute mountain sickness.
Caffeine, in contrast, counteracts these effects of adenosine in the brain’s circulation by causing vasoconstriction of those cerebral blood vessels, decreasing blood flow within the brain. Therefore, it is likely that caffeine can help prevent the onset of acute mountain sickness because of its ability to decrease cerebral vasodilation in response to hypoxia at high altitude.1 Caffeine is included in several over-the-counter headache medications, such as Excedrin Migraine, exactly for this purpose.
While there is no clinical data exhibiting that caffeine increases the rate at which individuals acclimate to living at high altitude from sea level, physiologic studies suggest that caffeine is helpful in increasing ventilation and decreasing hypoxia. Caffeine stimulates chemoreceptors in the brain and carotid arteries, altering the brainstem’s respiratory center in the medulla oblongata to become more sensitive to low blood oxygen saturation. As a result of this increased sensitivity to hypoxia, the lungs and respiratory muscles unconsciously increase their activity to increase resting ventilation rate and increase blood oxygen saturation.
During my six weeks at the Ebert Family Clinic for my pediatric medicine rotation, I measured my blood oxygen levels before and after drinking 12 oz of coffee. My results can be found in Table 2.
Table 2. Six-week average blood oxygen saturation pre- and post-consumption of 12 oz. coffee
|Pre-coffee oxygen saturation average:||Post-coffee oxygen saturation average:|
While these results are an anecdotal summary of my own experience living at high altitude and drinking coffee for six-weeks, drinking 12 oz. of coffee showed an average increase of blood oxygenation of 2%.
Caffeine Study at Everest
One study conducted at the base camp of Mt. Everest (17,600 ft) studied the 24-hour effect of caffeine in black tea ingested by one study group compared to a placebo group that only drank water. Both groups ingested the same volumes of liquid in the 24 hours. The study found that both groups had identical urine amounts at the end of the study, suggesting that caffeine did not lead to dehydration. Additionally, the tea-drinking group reported less fatigue and better mood compared to the placebo group.1
Caffeine Withdrawal at High Altitude
Caffeine cessation in fear of dehydration while travelling to high altitude destinations often leads to an exacerbated withdrawal reaction from caffeine, mimicking the symptoms of acute mountain sickness. This is due to the up-regulation, of adenosine receptors in the brain that become uninhibited in the absence of caffeine. As a result, adenosine binds to the increased amount of adenosine receptors in the brain causing excessive cerebral vasodilation and subsequent headache, nausea, vomiting, weakness, lethargy and confusion. Therefore, regular coffee drinkers or any type of caffeine users should avoid abrupt cessation of caffeine intake while traveling from sea level to high altitude.1
The above mentioned studies have not studied the effects of caffeine in caffeine-tolerant vs. caffeine-naïve individuals, but a trial of caffeine in the form of either coffee, tea or pill would be worthwhile in otherwise healthy individuals suffering from symptoms of acute mountain sickness while visiting high altitude locations. Future studies would benefit from comparing the effects of caffeine on caffeine tolerant individuals and individuals who do not consume caffeine on a regular basis. However, individuals must always consult their health care provider to determine if it is safe to use caffeine prior to consumption of caffeine products.
Michael Peterson, PA-S
University of St. Francis, Physician Assistant Program