A common drink pattern was linked to less sleep and more fatigue in soldiers

Researchers mapped recurring patterns of caffeine, energy drink, and sugar-sweetened beverage use to examine how everyday drinking habits intersect with sleep and recovery in active-duty personnel.

Study: Beverage Co-Consumption Profiles, Sleep, and Fatigue in Professional Army Personnel. Image Credit: Krakenimages.com / Shutterstock

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A recent study in the journal Nutrients found that a higher-frequency beverage co-consumption profile was associated with shorter sleep duration, lower sleep efficiency, and greater physical fatigue in a cross-sectional study of Spanish Army personnel.

Background

Nutrition is an important aspect of ensuring military readiness, supporting physical stamina, cognitive alertness and attention to environmental or task-related cues, recovery from demanding effort, and long-term health. Military foods and beverages should support these needs.

In the military, night duties, early starts, irregular shifts, deployment demands, and restricted sleep opportunities are common. This makes the use of stimulants like caffeine a common practice. This may, however, reinforce continued stimulant use.

Caffeine, according to the authors, is reported to increase alertness, reaction time, and endurance, especially under conditions of little sleep. Conversely, taking caffeine at the wrong time, or too much of it, may perpetuate reliance on stimulants and disrupt sleep.

Caffeine and sleep

Prior evidence suggests that caffeine reduces total sleep time by about 45 minutes, and decreases sleep efficiency. It also increases the time to sleep onset and wakefulness after sleep onset. These effects depend strongly on dose and timing.

Overall, the product, dose, frequency and timing of caffeine use, as well as individual susceptibility, influence its effects.

Energy drinks combine caffeine with sugar or non-nutritive sweeteners and often contain taurine, B vitamins, botanical extracts, or other bioactive ingredients. Frequent consumption of energy drinks by military personnel has been linked to fatigue, mental health issues, aggression, and poor sleep.

Similar associations have been observed among university students, starting at relatively low frequencies of use and showing a frequency-related gradient. For instance, energy drink use has been associated with insomnia.

In addition, studies have linked sugar-sweetened beverages to shorter sleep. However, none of these studies have established causality.

Reason for this study

The current study aimed to analyze the associations between co-occurring beverage behaviors and sleep duration, sleep efficiency, and physical fatigue in Spanish military personnel. These sleep characteristics and physical fatigue were selected as probably being recovery-related correlates.

The researchers examined the frequency of use of caffeinated drinks, energy drinks (which contain caffeine and may be sugar-sweetened), and sugar-sweetened beverages. They used latent class analysis to identify beverage-frequency profiles based on potential co-consumption patterns.

They assessed the association of these profiles with sleep and fatigue, after adjusting for occupational workload, training, smoking, alcohol intake, water intake, and military rank.

Study characteristics

This cross-sectional analysis included 1,155 participants on active duty from two cohorts (1,043 and 112 participants, respectively). Demographic and psychological details were collected through questionnaires, along with information on sleep, nutrition, beverage use, and the work environment.

However, the type of military activity at the time of questionnaire completion was not recorded, such as routine duty, guard duty, or field exercise.

They collected self-reported data on sleep duration (in hours per night), time in bed, and calculated sleep efficiency. Habitual physical fatigue was assessed in only 1,043 participants.

The study sample was mostly male, with 1,070 men and 85 women. The mean age was approximately 29 years and the average sleep duration was 6.1 hours.

Beverage consumption

About 47.7% of participants were estimated to belong to the lower-frequency profile, characterized by infrequent consumption of energy drinks and sugar-sweetened beverages. The estimated prevalences were 28.3% and 24% for the intermediate- and higher-frequency classes, respectively.

The intermediate-frequency profile was characterized by energy drink consumption 1-2 times per week. Participants with the higher-frequency profile had nearly an 85% probability of using energy drinks 3 or more times a week, as well as more frequent use of sugar-sweetened and caffeinated beverages.

Compared with the lower-frequency profile, the higher-frequency group tended to be younger, had a greater proportion of troops, and reported higher weekly training volumes. They were also more likely to be daily smokers.

After adjustment, the higher-frequency profile was associated with approximately 14 minutes less sleep per night than the lower-frequency profile. Sleep efficiency was about two percentage points lower and habitual physical fatigue was 0.4 points higher on the 0-10 scale.

Notably, the authors caution that the 14-minute difference in sleep duration should not be considered either clinically meaningful or clinically negligible because no validated minimal clinically important difference was specified. Without a comprehensive sleep assessment or objective measurements, the sleep-efficiency difference should be seen as a statistical association rather than a clinically meaningful or individually perceptible difference.

Similarly, the fatigue finding should be interpreted cautiously despite its statistical significance, as it may vary by setting. The observed sleep-fatigue associations are subject to reverse causation, which cannot be ruled out in an observational study.

Intermediate-versus-lower contrasts were not statistically significant.

Further sensitivity analyses using alternative measures of co-consumption showed associations in the same direction. However, when the three beverage indicators were entered simultaneously as separate standardized predictors, none of the individual coefficients reached statistical significance.

Notably, these profiles are probably overlapping beverage-frequency response patterns rather than representing specific thresholds of caffeine or sugar intake.

The study thus shows “a recurring co-consumption response profile for prospective evaluation rather than establishing a harmful beverage combination.” This calls for more targeted evaluations and does not support punitive restrictions based on these findings.

Limitations

Despite the large sample size and the use of sophisticated statistical methods, the beverage-frequency questions have not been validated, nor have they provided information about multiple attributes of the beverages in question. Thus, they do not represent caffeine dosage or sugar intake categories. The broad caffeinated-beverage question also explicitly included energy drinks, creating partial overlap between two of the indicators.

Self-reported sleep and fatigue measures may have introduced measurement error. The exact type of military activity at the time of questionnaire completion was not recorded, leaving the possibility of residual confounding. Other potential confounding factors might include differences in shift timing, chronotype, medications and supplements, baseline health, and unit culture.

The sample consisted of Spanish Army personnel, mostly men, limiting its generalizability to women, other service branches, and non-military personnel.

Weekly training volume was measured differently in the two cohorts that made up the final sample. Missing outcome and covariate data also reduced model-specific sample sizes. Finally, the observational design precludes causal inference.

Conclusions

The study found three co-consumption response profiles based on the frequency of use of caffeinated beverages, sugar-sweetened beverages, and energy drinks. The higher-frequency profile was associated with lower sleep efficiency, shorter sleep duration, and greater habitual physical fatigue than the low-frequency profile.

However, the clinical or perceptual importance of these findings remains to be established, given the self-reported nature of the data and the absence of validated, clinically meaningful thresholds for these measures in this setting. The observational design also precludes causal inference.

Future studies should include specific questions to assess the type and dose of exposure, the duty context, the purpose of use, and the timing relative to fatigue and sleep.

In addition, they should use objective or longitudinal measurements of sleep and fatigue. Such research could help establish the direction of association and its persistence over time.

Journal reference:

• Clemente-Suárez, V. J., Florian, J., Yáñez-Sepúlveda, R., et al. (2026). Beverage Co-Consumption Profiles, Sleep, and Fatigue in Professional Army Personnel. Nutrients. DOI: 10.3390/nu18172930, https://www.mdpi.com/2072-6643/18/17/2930