Current research demonstrates the long-reaching impacts of stressors, such as famine on metabolic, cardiovascular and cerebral health ( 15). Therefore, these differential impacts may result in different health outcomes where a one-size-fits-all treatment approach will be ineffective. Second, both military and civilian populations may witness and experience the long-term physical, psychological and economic impacts of war, but it is, in most instances, only military personnel who are expected to actively participate in planned, targeted assault. First, as the rigorous military selection process generates a population of highly fit and healthy individuals compared to general society. Exploring whether military populations differ epigenetically in response to conflict when compared to civilians is important. Our review discusses epigenetic impacts and phenotypic outcomes on individuals and families affected by conflict and war, summarised in Figure 1. Non-genetic influence includes the impact of experiences from previous generations, passed down through shared stories or the spoken word, an effect referred to as “intergenerational trauma,” which may contribute to PTSD ( 12– 14). Such inheritance is termed “intergenerational”, except in instances where the generation could never have been exposed to stress stimuli (e.g., the grandparent was not pregnant at the time), in which case it is “transgenerational” ( 11).

Epigenetic modifications may be inherited by progeny, and even in the offspring of progeny. Epigenetics may impact the individual, for example, work-related stress and depression result in altered DNA methylation of the glucocorticoid receptor (GR) gene ( NR3C1 nuclear receptor subfamily 3 group C member 1), an area well reviewed by Bakusic et al. The epigenome, a collaborative effort of DNA and its modifications, can be readily modified in response to internal and external changes ( 1– 9). Future large-scale studies further identifying the heritable risks of war, as well as any potential differences between military and civilian populations, would be valuable to inform future healthcare directives. A limited number of studies also revealed hereditary effects of war exposure across groups: decreased cortisol levels and a heightened (sex-linked) mortality risk in offspring. Genes associated with sleep ( PAX8 LHX1) are seen to be differentially methylated in veterans.

We also note that, despite a potential “healthy soldier effect”, both veterans and civilians with PTSD exhibit the altered DNA methylation status in hypothalamic–pituitary–adrenal (HPA) axis regulatory genes such as NR3C1. In this state-of-the-science narrative review based on systematic principles, we summarise existing data to explore the outcomes of these exposures especially in veterans and show that they may result in an increased likelihood of developing gastrointestinal, auditory, metabolic and circadian issues, as well as post-traumatic stress disorder (PTSD). War and conflict are global phenomena, identified as stress-inducing triggers for epigenetic modifications. 8Northern Hub for Veterans and Military Families Research, Department of Nursing, Midwifery and Health, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, United Kingdom.7Centre for Cardiovascular Biology and Medicine, University College London, London, United Kingdom.6Development, Ageing and Disease, UCL Institute of Ophthalmology, University College London, London, United Kingdom.5Haxby Group Hull, General Practice Surgery, Hull, United Kingdom.4St George’s Hospital Medical School, London, United Kingdom.3Hull York Medical School, University of York, York, United Kingdom.

2BRAVO VICTOR, Research & Innovation, London, United Kingdom.

1Research & Innovation, Blind Veterans UK, London, United Kingdom.

Intergenerational trauma genetic