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Institute of Medicine (US) Committee on Military Nutrition Research. Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. Washington (DC): National Academies Press (US); 2001.

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Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations.

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1Basic Concepts


Optimal job performance without compromising the health and well-being of the worker is the goal of employers regardless of the field of endeavor. Intermittent or prolonged physiological and psychological stressors that employees bring to the workplace have an impact not only on their own performance but also on those with whom they work and interact. The internal stressors an individual brings to his or her job are compounded by the day-to-day physical and mental stressors of the job itself. Military personnel in combat settings endure highly unpredictable timing and types of stressors as well as situations that require continuing vigilance for long periods of time.

The U.S. military's concerns about the individual war fighter's ability to avoid performance degradation and the need to enhance mental capabilities in highly stressful situations have led to an interest in devising military ration components that could enhance physical and cognitive performance.

Previous Committee on Military Nutrition Research Recommendations

In 1992 the Committee on Military Nutrition Research (CMNR) was asked by the U.S. Army Medical Research and Materiel Command to evaluate the potential of selected amino acids, carbohydrates, structured lipids, choline, carnitine, and caffeine to enhance performance. The committee was asked to address two questions: first, whether the use of diet components or supplements to enhance physical and mental performance in “normal” healthy, young adult soldiers was a fruitful approach and, second, which food components, if any, would be the best candidates for enhancing military mental and physical performance. In response to this request the committee held a workshop, reviewed the scientific literature, and published the report, Food Components to Enhance Performance (IOM, 1994), in which it recommended continued research on the mechanisms of the effects of caffeine on cognitive performance, mood, and alertness. It was noted that particular attention should be paid to maximizing positive effects when performance is already degraded.

Specifically, the committee recommended:

Caffeine definitely should be considered in developing performance-enhancing rations or ration components. Caffeine is safe as a component of food at doses required to overcome sleep deprivation and has already been included in diets of military personnel via coffee and many soft drinks. Since many soldiers may not normally drink coffee, a mechanism for including caffeine in another ration component that can be selectively used when the situation requires should be evaluated. It appears that doses of 300–600 mg/70 kg person will achieve the desired stimulus in those nonhabituated to caffeine; additional research needs to be conducted to determine the effects of this level of caffeine in those with higher habitual intakes. (IOM, 1994, p. 50)

The Current Situation

Changes in military operations over the last 50 years have forced continued assessment and adoption of technologies that will sustain or enhance physical and cognitive performance of the individual service member. This urgency in maintaining and enhancing performance is fostered by increased reliance on the individual's cognitive skills in the operation and maintenance of complex military equipment in an ever-increasing variety of environmental conditions. Today's military relies heavily on the use of computer-controlled systems that require highly trained and alert operators. In addition, there is greater reliance on rapid mobility to enable deployment at any time to achieve the nation's military objectives. The urgency of maintaining and enhancing performance is also driven by constant pressure, due to personnel reductions, to have the individual perform for longer periods of time with less sleep, shorter transition times, less recovery time between missions, and less reliance on traditional logistical support.

These scenarios can have severe impacts on the individual's level of fatigue, alertness, response time, mood, judgment, reliability in decision making, and other cognitive skills. Increased likelihood of decrements in cognitive function is coupled with greater dependence on each individual in accomplishment of the mission. Both of these factors have a profound impact on the success or failure of a military operation.

In its effort to sustain and enhance the performance of personnel, the military's emphasis should be placed on providing adequate levels of nutrients, water, life support equipment, clothing, and, to the extent possible, sleeping regimens, appropriate rest areas, and work patterns. After these efforts have been put in place, the potential use of dietary supplements and selected pharmaceuticals is an appropriate consideration.


In addition to its natural occurrence in some foods, caffeine is used as a food additive and as a drug or a component of many pharmaceutical preparations. It is the most widely consumed psychoactive or central nervous system (CNS) stimulant in the world (Curatolo and Robertson, 1983). When administered in the doses commonly found in beverages and drugs, it has measurable effects on certain types of human performance. It is readily available to both the civilian and the military populations as a beverage (coffee, tea, maté), food (cocoa products), food additive (soft drinks, bottled water), and pharmaceutical (over-the-counter pain and weight-loss medications, numerous prescription drugs). No other substance has this combination of uses.

As a food additive caffeine is generally considered safe based on its long history of use and on extensive research conducted throughout the world for more than a century. However, despite this long history of use, modern epidemiological techniques have raised concerns about associations between continued use of high levels of caffeine and long-term health.

Caffeine (1,3,7-trimethylxanthine) and the related methylxanthines, theobromine (3,7-dimethylxanthine) and theophylline (1,3-dimethylxanthine), are widely distributed in plants throughout the world. More than 60 different plant species containing caffeine have been identified, and history suggests that it may have been consumed, in one form or another, as far back as the Paleolithic period (Barone and Roberts, 1996). The primary sources of these compounds are coffee (Caffea arabica), kola nuts (Cola acuminata), tea (Thea sinensis), and chocolate (Cocoa bean). Although the actual discoverer of caffeine as a stimulant is unknown, legend has it that it was first discovered in Ethiopia in the third century AD when a shepherd noticed that his goats became very frisky and agitated after eating coffee berries or “beans”. The shepherd tried chewing some of the berries and noted their stimulant properties. An abbot at a nearby monastery brewed the beans in hot water and found that the beverage helped him to stay awake during long nights of prayer. Cultivation of the coffee plant may have begun as early as the sixth century AD, probably in Ethiopia. Elsewhere in Africa, coffee berries were crushed and mixed with fat to serve as a food to stimulate warriors in battle. By approximately 1000 AD, coffee reached Yemen, where the beverage became very popular and drinking it a social ritual among Muslims. From there it spread to Europe and the Americas. All stable indigenous cultures having access to caffeine-containing plants have developed drinks or foods containing these stimulant products. The earliest recorded use of caffeine-containing beverages dates back to the Tang Dynasty of China (618–907 AD) where tea was a popular drink believed to prolong life.

Caffeine Content of Common Food Sources

The amount of caffeine in commonly consumed beverages and other products varies a great deal (Table 1–1), from as little as 5 mg/8 oz of chocolate milk, to as much as 300 mg/6 oz of strong espresso coffee. Since early times the adverse effects of very large doses of caffeine, especially in those who are not used to the product, have been noted. The reported signs and symptoms include nervousness, anxiety, insomnia, irregular heartbeats, excess stomach acid, and heartburn (Duke, 1988).

TABLE 1–1. Caffeine Content of Some Common U.S. Food Products.


Caffeine Content of Some Common U.S. Food Products.

Caffeine Intake of Adults

Based on the available product usage data and food consumption data, Barone and Roberts (1996) estimated caffeine intakes in the United States, United Kingdom, Denmark, and Australia. The per capita daily caffeine intake for all U.S. adults was approximately 3 mg/kg body weight (BW) (for a 60–70-kg person). For adults who actually consumed caffeine products, mean daily intake was 4 mg/kg BW, and for the ninetieth percentile of caffeine users, intakes approximated 5–7 mg/kg BW.

Caffeine intake was higher in the United Kingdom, with per capita daily consumption being 4 mg/kg BW and 7.5 mg/kg BW for the ninetieth percentile of caffeine users. Consumption was highest in Denmark: 7.0 mg/kg BW for all adults and 14.9 mg/kg BW for the ninetieth percentile of caffeine users.


Surveys indicate that more than 90 percent of the military population consumes caffeine at some level on a daily basis. A small-sample survey reported by Lieberman (1999) indicated that mean caffeine intake among military personnel was 340 mg/d. The majority of those sampled consumed 200 mg/d or less; however, consumption levels were highly variable and thus physiological effects cannot be generalized. Typically, older personnel consumed more caffeine than younger ones, and males consumed slightly more than females. The majority of caffeine (about 70 percent) was consumed as coffee, 23 percent as soda, 5 percent as tea, and slightly less than 2 percent as chocolate, with the remainder coming from medications. These factors make it difficult to determine risk and to make risk management decisions on the use of caffeine for maintenance and enhancement of cognitive performance in military operations.

The military requested the committee's assistance in this decision-making process. The CMNR was requested to evaluate the relevant caffeine research, including all relevant studies performed since the 1992 workshop, and address in a brief report the following proposal and questions to assist the Department of Defense in the transition of research to military application. Specifically, the military provided the following information and questions for the committee's response.

A specific transition opportunity could take the following form: a “HOOAH” food bar (a nutrient-dense energy bar developed by the Army) containing 600 mg of caffeine, scored in 150-mg increments, with labeling that provides specific guidance for use of up to one food bar (600 mg) to offset deficits in cognitive function and situational awareness produced by inadequate restorative sleep and during military operations at night. The label should also contain warnings, especially for infrequent or noncaffeine users, that no more than one scored segment (150 mg) should be used in the first hour and should be discontinued if undesirable changes in hand steadiness, pulse, and respiration occur. This performance-enhancing ration component could be provided separately or as part of operational rations. Alternatives to be considered include coffee, caffeinated soft drinks, modifications of the HOOAH bar dose, caffeinated chewing gum, caffeine pills, amphetamine pills (dexedrine), and sustained-release caffeine. The intent is to provide a pharmacological/dietary supplement strategy to significantly counter performance deficits in special circumstances when doctrinal and behavioral solutions (adherence to appropriate work-rest cycles, naps, etc.) are not possible or break down. The key questions to be addressed:


Efficacy: Does the committee stand by its earlier recommendation that there are sufficient data to recommend a caffeine product to enhance performance, and what are the specific indications for use (e.g., vigilance activities following inadequate sleep) and contraindications for use (e.g., tasks involving fine motor coordination)?


Safety: What are the medical risks to individuals associated with ready availability of caffeine, including acute health risks (e.g., cardiac arrhythmia, caffeine psychosis), long-term health risks (e.g., hypertension, hypercholesterolemia), potential interactions with other drugs (e.g., ephedra-containing supplements) or factors specific to military operations (e.g., heat stress, stress reactions), and potential problems of habituation of use (e.g., tolerance, caffeine dependence)?


Dose and warning labels: What dose level(s) should be recommended to (a) habituated caffeine users and (b) nonhabituated users? What warnings should be provided on such a product in the context of ethical, religious, and potential caffeine habituation concerns?


Alternatives: Are there practical alternatives to caffeine, which would better serve the intended purpose of enhancing performance in fatigued service members (e.g., amphetamine)?


Formulation: (a) Does the inclusion of other components (e.g., glucose) improve beneficial effects of caffeine in sustained operations (SUSOPS), as previously suggested by the committee? (b) Is there a better approach to caffeine delivery than the HOOAH bar (e.g., is it better to have more rapid absorption and action using caffeinated chewing gum, longer duration of action using sustained-release caffeine products, or pill or beverage formulations)?

A workshop was organized to review the scientific data on the efficacy of caffeine in maintaining physical and cognitive performance in military operations, its safety, and appropriate formulations for administration during military operations and to identify any ethical or other considerations. Another purpose of this workshop was to compare the effectiveness of caffeine to other pharmaceuticals that have CNS effects.

The research presented at this workshop addressed many of these issues. Information from the speaker presentations and the published scientific literature, as well as the deliberations of the CMNR, were used in the preparation of this report.

NOTE: It is important to emphasize that the responses to the questions and recommendations in this report are specific to military operations and are not necessarily applicable to the needs of the civilian population. In particular, it is recognized that mental alertness and vigilance in situations of sleep deprivation may be necessary during military operations in order to achieve mission objectives. In the civilian environment, taking large doses of caffeine to offset lack of sleep in situations where public safety and health could potentially be compromised, such as in the operation of aircraft, motor vehicles, heavy equipment, delicate life-saving procedures, and the like, is not justified.

Copyright 2001 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK223799


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