Enhancing or preserving cognitive performance of personnel working in stressful, demanding and/or high tempo environments is vital for optimal performance. Emerging research suggests that the human gut microbiota may provide a potential avenue to enhance cognition. This review examines the relationship between the human gut microbiota, including modulators of the microbiota on cognition and/or brain function. For this narrative review, a total of n = 17 relevant human research items of a possible 1765 published between January 2010 and November 2018 were identified. Two overarching design methods for synthesis were observed: correlational or pre/post intervention. Limited correlational design studies linking microbiota to cognitive/brain structure endpoints existed (n = 5); however, correlations between microbiota diversity and enhanced cognitive flexibility and executive function were observed. Gut microbiota intervention studies to improve cognition or brain function (n = 12) generally resulted in improved cognition (11/12), in which improvements were observed in visuospatial memory, verbal learning and memory, and aspects of attentional vigilance. Limited studies were available to draw a detailed conclusion; however, available evidence suggests that gut microbiota is linked to cognitive performance and that manipulation of gut microbiota could be a promising avenue for enhancing cognition which warrants further research.

Intake of dietary supplements has increased, despite evidence that some of these have adverse side effects and uncertainty about their effectiveness. This systematic review examined the evidence for the cognitive benefits of a wide range of dietary supplements in healthy young adult samples; the aim was to identify if any might be useful for optimising cognitive performance during deployment in military personnel. Searches were conducted in 9 databases and 13 grey literature repositories for relevant studies published between January 2000 and June 2017. Eligible studies recruited healthy young adults (18–35 years), administered a legal dietary supplement, included a comparison control group, and assessed cognitive outcome(s). Thirty-seven of 394 identified studies met inclusion criteria and were included for synthesis. Most research was deemed of low quality (72.97%; SIGN50 guidelines), highlighting the need for sound empirical research in this area. Nonetheless, we suggest that tyrosine or caffeine could be used in healthy young adults in a military context to enhance cognitive performance when personnel are sleep-deprived. Caffeine also has the potential benefit of improving vigilance and attention during sustained operations offering little opportunity for sleep. Inconsistent findings and methodological limitations preclude firm recommendations about the use of other specific dietary supplements.

Dietary supplements (DSs) and nutritional supplements (NSs) can enhance performance, recovery or training adaptations, however, some substances, dosages, and usage protocols are unsafe. Knowledge of the type and extent of use within populations enables strategies to be formulated to promote safe and effective use (where needed) and to avoid adverse side effects. The purpose of this study was to understand DS and NS use by active-duty Australian soldiers. Surveys were distributed by e-mail and hard copy to eligible participants (n = 23,195). Respondents (males n = 1833; females n = 296) comprised 9.3% of the total population. Use of ≥1 DSs/week was reported by 76.4% of males and 86.8% of females, and use of ≥1 NSs/week was reported by 21.7% of males and 20.9% of females. The most commonly used supplements were protein or amino acids (55.6%), multivitamins and minerals (38.2%), other DSs (37.8%), individual vitamins and minerals (33.0%), and combination products (32.8%). Logistic regression revealed the number of DSs respondents used simultaneously was significantly different between males and females, age groups, BMI ranges, and body weight actions. Engagement in special operations was a significant predictor of the use of any DS, individual vitamin and minerals and multivitamin and minerals. Approximately 16% of regular DS users reported experiencing one or more side effects, with the most common being palpitations (10.6%), tingling or numbness in the face, fingers, arms, or legs (5.5%), tremors or shaking (2.9%), flushing (2.3%), headache (2.0%), abdominal pain (1.6%), anxiety (1.4%), and dizziness or confusion (0.9%). The results revealed more prevalent use of several categories of DSs and NSs among some subgroups. Ongoing surveillance of DS and NS use is important for tracking trends in use over time and gauging the effectiveness of any strategies employed to enhance the quality of supplement use.