Suicide after leaving the UK Armed Forces 1996-2018: A cohort study.

BACKGROUND: There are comparatively few international studies investigating suicide in military veterans and no recent UK-wide studies. This is important because the wider context of being a UK Armed Forces (UKAF) veteran has changed in recent years following a period of intensive operations. We aimed to investigate the rate, timing, and risk factors for suicide in personnel who left the UKAF over a 23-year period. METHODS AND FINDINGS: We carried out a retrospective cohort study of suicide in personnel who left the regular UKAF between 1996 and 2018 linking national databases of discharged personnel and suicide deaths, using survival analysis to examine the risk of suicide in veterans compared to the general population and conditional logistic regression to investigate factors most strongly associated with suicide after discharge. The 458,058 individuals who left the UKAF accumulated over 5,852,100 person years at risk, with a median length of follow-up of 13 years, were mostly male (91%), and had a median age of 26 years at discharge. 1,086 (0.2%) died by suicide. The overall rate of suicide in veterans was slightly lower than the general population (standardised mortality ratio, SMR [95% confidence interval, CI] 94 [88 to 99]). However, suicide risk was 2 to 3 times higher in male and female veterans aged under 25 years than in the same age groups in the general population (age-specific mortality ratios ranging from 160 to 409). Male veterans aged 35 years and older were at reduced risk of suicide (age-specific mortality ratios 47 to 80). Male sex, Army service, discharge between the ages of 16 and 34 years, being untrained on discharge, and length of service under 10 years were associated with higher suicide risk. Factors associated with reduced risk included being married, a higher rank, and deployment on combat operations. The rate of contact with specialist NHS mental health services (273/1,086, 25%) was lowest in the youngest age groups (10% for 16- to 19-year-olds; 23% for 20- to 24-year-olds). Study limitations include the fact that information on veterans was obtained from administrative databases and the role of pre-service vulnerabilities and other factors that may have influenced later suicide risk could not be explored. In addition, information on contact with support services was only available for veterans in contact with specialist NHS mental health services and not for those in contact with other health and social care services. CONCLUSIONS: In this study, we found suicide risk in personnel leaving the UKAF was not high but there are important differences according to age, with higher risk in young men and women. We found a number of factors which elevated the risk of suicide but deployment was associated with lower risk. The focus should be on improving and maintaining access to mental health care and social support for young service leavers, as well as implementing general suicide prevention measures for all veterans regardless of age.

Sediment microbial assemblage structure is modified by marine polychaete gut passage.

Invertebrate activities in sediments, predominantly the redistribution of particles and porewater, are well-known to regulate the structure of associated microbial assemblages; however, relatively little attention has been given to the effects of sediment ingestion, gut passage and excretion by deposit-feeding invertebrates. Here, we use high-throughput sequencing and quantitative PCR to examine how passage through the gut of the marine polychaete Hediste diversicolor affects the structure of bacterial and archaeal assemblages and the abundance of nitrogen cycling taxa. We show that the digestive tract of H. diversicolor contains unique transitory microbial assemblages that, during gut passage, become more like the surrounding sediment assemblages. Enrichment of similar microbial taxa in both the hindgut and the burrow wall suggest that these transitory gut assemblages may influence the composition of the local sediment community. The hindgut of H. diversicolor also forms a reservoir for unique ammonia-oxidising archaeal taxa. Furthermore, distinct microbial assemblages on external polychaete surfaces suggest that deposit-feeding invertebrates act as vectors that transport microbes between sediment patches. Collectively, these findings suggest that the passage of sediment and associated microbial assemblages through the gut of deposit feeding invertebrates is likely to play a significant role in regulating sediment microbial assemblages and biogeochemical functioning.

Polychaete mucopolysaccharide alters sediment microbial diversity and stimulates ammonia-oxidising functional groups.

Sediment nitrogen cycling is a network of microbially mediated biogeochemical processes that are vital in regulating ecosystem functioning. Mucopolysaccharides (mucus) are produced by many invertebrates and have the potential to be an important source of organic carbon and nitrogen to sediment microorganisms. At present, we have limited understanding of how mucopolysaccharide moderates total sediment microbial communities and specific microbial functional groups that drive nitrogen cycling processes. To start addressing this knowledge gap, sediment slurries were incubated with and without Hediste diversicolor mucus. Changes in dissolved inorganic nitrogen (ammonia, nitrite and nitrate) concentrations and bacterial and archaeal community diversity were assessed. Our results showed that mucopolysaccharide addition supported a more abundant and distinct microbial community. Moreover, mucus stimulated the growth of bacterial and archaeal ammonia oxidisers, with a concomitant increase in nitrite and nitrate. Hediste diversicolor mucopolysaccharide appears to enhance sediment nitrification rates by stimulating and fuelling nitrifying microbial groups. We propose that invertebrate mucopolysaccharide secretion should be considered as a distinct functional trait when assessing invertebrate contributions to sediment ecosystem function. By including this additional trait, we can improve our mechanistic understanding of invertebrate-microbe interactions in nitrogen transformation processes and provide opportunity to generate more accurate models of global nitrogen cycling.