Is Alcohol More Potent at Altitude?
Is alcohol more potent at altitude than at ground level? This is an interesting question that appears thoroughly answered according to the many travel advice columns that invariably warn to take care when flying not to drink as much in the air as at ground level because “scientific studies indicate that 1-2 drinks at ground level will have the effect of 3-4 at altitude.” Even an informal poll of some of my well-traveled friends echoed the same sentiment. Since this is our Vacation Issue, it seemed appropriate to investigate the mechanism of this apparent synergistic effect of altitude on alcohol.
The prevailing notion in the travel industry is that altitude exerts a synergistic effect on alcohol. A synergist is a substance or condition that affects the potency of another substance. For example, caffeine enhances the analgesic effect of aspirin, which is why caffeine is found in some pain relievers. The same dose of aspirin has a much more potent effect with the addition of caffeine. The popular conception is that altitude exerts a synergistic effect on alcohol. Numerous sources reiterate this notion. “Alcohol is 2-3 times more potent when flying. One glass of wine has the effect of 2-3 glasses on the ground.” (as noted in The Indian Society of Aerospace Medicine “Aircrew Sleep Civil & Military Operations”) Apparently the notion of greater alcohol effects at altitude emanates from a study by McFarland in 1953 based on earlier studies from 1936 and 1949 that stated that the alcohol in “2-3 cocktails would have the physiological effect of 4-5 at altitude.” He based this assumption on the idea that the lower oxygen levels at altitude would impair the body’s ability to metabolize alcohol leading to a faster and greater buildup of alcohol in the system i.e. more drunk.
The concept of oxygen deprivation impairing alcohol metabolism seemed worthy of additional investigation. To detoxify alcohol, the body metabolizes it primarily with an enzyme called alcohol dehydrogenase. This reaction converts alcohol to acetaldehyde, a chemical that does not have the same intoxicating effects of alcohol. However, the reaction catalyzed by alcohol dehyrogenase does not require oxygen directly, which questions the hypothesis that lower levels of oxygen at altitude could impair alcohol metabolism. This prompted me to dig deeper into the literature to see what studies have been performed on the effect of alcohol and altitude. I found some interesting results.
Interestingly, several studies examined the effects of altitude on blood alcohol level (BAC), or in other words, does altitude change alcohol metabolism. In two separate reports for the Federal Aviation Administration (FAA) in 1968 and 1970, E.A. Higgins examined the differential effects of alcohol at ground level and altitude using a pressure chamber to simulate altitude. Blood samples were drawn at intervals to determine BAC of the test subjects. These studies showed no difference in BAC between ground level and altitude. BAC however, may only be part of the story.
The blood alcohol level and behavior at altitude also needed investigation in case a synergistic effect was occurring the BAC alone could not measure. W.E. Collins published a complex study on “Performance effects of alcohol intoxication and hangover at ground level and altitude,” in 1980 for Aviation, Space, and Environmental Medicine. This study tested the effects of alcohol at ground level and the simulated altitude of 12,000 ft. in an altitude chamber on the performance of a tracking task (something pilots should do very well). Interestingly, the study found that both alcohol and altitude significantly impaired performance scores, but no alcohol/altitude interaction was observed. This study did lack clarity due to the complex effects of fatigue, which prompted further study.
W.E Collins et al. looked to replicate the findings in the 1980 study of alcohol at altitude that lacked the fatigue component in a report in July of 1985 for the FAA titled “Some effects of alcohol and simulated altitude on complex performance scores and breathalyzer readings.” The authors studied 17 men between 21 and 35 years of age who reported could manage 4 to 5 drinks in a short period of time. Each subject participated in all four aspects of the trial—placebo (non-alcoholic rum extract in a mixer) or alcohol at ground level or at an altitude of 12,000 feet simulated with an air mixture delivered via a mask. Blood alcohol levels were determined using a Breathalyzer and were found to be the same at ground level and altitude.
To assess the effects of alcohol and altitude, the test subjects performed a series of tests called the Civil Aeromedical Institute Multiple Test Performance Battery (MTPB) at with and without alcohol at ground level and altitude. This battery of tests ranges over 50 minutes from low to moderate to heavy workload. The tests included tracking and monitoring exercises, mental arithmetic, problem solving, and pattern recognition.
Alcohol reduced MTPB scores as expected at ground level and at altitude but altitude alone also affected test scores. The highest MTPB scores were recorded under placebo conditions at ground level. Interestingly altitude alone also depressed test scores; the MTPB test showed statistically significant depression of test scores at altitude under placebo conditions. The scores as a whole were reduced by as 1.8% of control by altitude. This means that altitude alone impairs physical and mental abilities. Altitude alone decreased performance in arithmetic, target identification and most of the other tests. Alcohol much more significantly reduced performance scores both at ground level and at altitude. “the addition of altitude to the alcohol conditions further depressed performance scores but to the same extent that placebo scores were depressed by altitude.” (W.E Collins et al.) In these experiments each test subject drank about 4 drinks in the first hour, and the greatest impairment was observed at the second hour with composite test scores reduced by about 9.6% at ground level and 10.1% at altitude. These numbers indicate that altitude does lower the alcohol scores compared to alcohol at ground level but by a small amount. The decrease is the equivalent of after having four drinks taking a sip off of another. In essence the researchers did not observe any synergistic effect (increase in alcohol potency) of alcohol and altitude, certainly not to the extent of doubling the potency of alcohol at altitude.
The previously described studies looked at the relationship between altitude, BAC and the ability to perform certain tasks. Another study looked directly at nervous function under placebo and alcohol at ground level, 5,280 ft. Denver, CO and altitude, 14,264 ft. on Mount Evans, CO. This study by Freedman et al monitored the electrical function of the auditory response in the human brain to two sequential clicks also called the two click test. Normally, the sound of a click generates an excitatory pulse in the brain, and the same click administered a short time later is dampened by the nervous system by an inhibitory mechanism; this response can be monitored with electrodes taped to the subject. In other words, the brain notices the first click by slightly amplifying it, but the brain dampens the volume of the subsequent click thereby reducing the brains attention to it. The initial response of amplification of a click puts the brain on alert, but the brain diminishes the subsequent click so as to let the brain not be distracted by some repetitive sound. Just in the way that birds chirping can catch your attention, but will fade from attention after a while. Freedman et al. found that alcohol reduced the initial response to the conditioning click but also decreased the dampening normally observed with the second or test click. Alcohol appears to diminish the brains alerting system but also diminishes the brains ability to dampen a subsequent click. The authors were curious to see if altitude would affect the results of this test, and the test was repeated on Mount Evans with a group of subjects from the ground level test. To the authors’ surprise, the results of the test were the same at altitude as a ground level—no alcohol/altitude interaction observed at the nervous level.
Flying in an airplane exposes passengers to altitudes not normally experienced by ground dwellers and much mythology has grown over the years about the effects of hailing the drink cart at altitude. A number of studies have been conducted that look at the interaction of alcohol and altitude. These studies examined the alcohol/altitude interaction from a metabolic level by measuring blood alcohol level, from a behavioral level with various performance tests, and from a physiological level measuring nervous function. From these studies alcohol and altitude do not appear to interact. Apparently altitude itself impairs function without the help of alcohol, and furthermore, alcohol appears work with the same potency at ground level as at altitude. Research indicates that the two to three times magnification of alcohol’s effects at altitude really is an urban myth perpetuated from speculations made over 50 years ago. However, the fact that altitude affects function, albeit no more than a few sips off your martini, does invite further research. Perhaps, this small difference affects people in a way not measured in experiments to date, or people are feeling more how they expect to feel when having a drink while cruising at 35,000 feet. Let’s do more studies.