A systematic review of hormonal changes, their effects on, and associations with, cognitive performance within defence and security personnel

Operational success in defence and security (D&S) often depends on personnels’ cognitive capabilities, which are likely influenced by endocrine fluctuations. Several investigations into the effect of hormonal manipulations on cognitive task performance exist, therefore, we undertook a systematic review to identify and assess the associations between hormones and cognitive performance. We searched MEDLINE, Embase and PsycNET in January 2024 for controlled interventions of hormones involving D&S participants. Each study featured at least one of six hormones (testosterone, oestrogen, cortisol, oxytocin, growth hormone, melatonin). Article screening was conducted independently and in duplicate according to preregistered inclusion/exclusion criteria. Assessing study and participant details, prioritisation grids helped to identify existing hormone-performance measures and highlight any gaps. Study quality appraisals and a narrative synthesis of findings concerning hormonal impacts on cognitive performance were also completed. Twenty articles from North American and Western European research groups met the inclusion criteria. Cortisol and testosterone were investigated the most, whereas oestrogen, oxytocin, growth hormone, and melatonin were less studied within D&S populations. Studies involved a greater proportion of male personnel across land, air, and sea domains. Generally, hormonal concentrations deviating from “normal” levels appeared to predispose psychophysiological states that prompt poorer cognitive performance. However, most studies were appraised as low-moderate in quality as studies were suffused with methodological concerns including high participant attrition rates, a widespread lack of blinding, randomisation, or a-priori sample size calculations. Consequently, for researchers to deduce any meaningful understanding of hormone-performance relationships within D&S contexts, future research must develop the existing evidence base.