The Influence of Psychosocial and Lifestyle Factors on Illness and Injury in British Army Recruits

Starting military training represents for many a major life transition. Both the high physical and high psychological demands of military training are thought to increase the risk of illness and injury in military recruits, however, the role of these demands in military recruits undertaking Army training is not well understood. In young adults embarking on basic military training, this thesis aimed to examine how childhood adversity and sleep behaviour influence infection and injury risk and whether changes in psychosocial and lifestyle factors during training impact the influence. In Chapter 4, childhood adversity, particularly exposure to multiple or abuse-related events, was associated with a significantly higher risk of respiratory tract infection (RTI) during adulthood. This relationship persisted after adjusting for potential confounders, demonstrating that early-life adversity exerts a lasting impact on adult immune function. Perceived stress and poor sleep quality during training partially account for this relationship. Chapter 5 examined the protective role of optimism on the relationship between childhood adversity and RTI. Recruits with a history of childhood adversity who showed increases in optimism across the first month of training exhibited no increased RTI risk, whereas those with decreases in optimism were over five times more likely to suffer RTI. Chapters 6 – 8 focused on the role of sleep on illness and injury. In Chapter 6, sleep restriction significantly increased upper respiratory tract infection (URTI) risk; however, this association was moderated by perceived sleep quality (PSQ). Recruits experiencing sleep restriction who reported good PSQ were at no greater risk of URTI compared to non-sleep-restricted individuals, whereas those with sleep restriction and poor PSQ were twice as likely to suffer infection. Chapter 7 extended these findings, demonstrating that poor sleep quality, independent of sleep duration, was consistently associated with increased RTI risk throughout training. Recruits who improved their sleep quality from civilian life to training were protected against infection, while those with enduring poor sleep were most at risk. Finally, Chapter 8 demonstrated that poor sleep quality and short sleep duration were associated with higher incidence of musculoskeletal injury (MSKI). Recruits with poor or short sleep were three to four times more likely to sustain an injury during training, suggesting that sleep disturbances compromise MSKI integrity. Collectively, this thesis presents novel evidence that both early-life psychosocial experiences and current behavioural factors shape adult health outcomes during military training.