Theme 3: the negative influence of prison-related situational and environmental factors on sleep
A range of prison-related situational and environmental factors was reported as negatively affecting sleep. Sleep was reported to be affected by factors such as light [46], [48] and ∗[49]; heat [47] and [67]; isolation [48] and ∗[49]; and noise ∗[22], [43], [44] and [48]. In one study, prisoners with insomnia reported significantly more environmental noise (e.g., prison officers talking) three or more times a week than good sleepers (31.7% and 1.6% respectively) [48]. As a consequence of incarceration, some prisoners also reported negative effects on sleep due to worry, guilt and judgement related to their crime [48] and ∗[49]; prolonged imprisonment [48]; and/or fear of violence [48] and [60]. Moreover, insomnia was also associated with inadequate sleep hygiene including daytime inactivity [48] and/or high caffeine and nicotine intake [53]. No studies reported on the impact of bedroom set-up (e.g., mattress quality etc.) nor compared perceived sleep quality before and after incarceration. Some studies used a random sample and compared prisoners with insomnia and good sleepers [48] and ∗[49]. However, the evidence was almost exclusively from Swiss remand prisons (i.e., unconvicted), the sample sizes were relatively low and thus some variables were positive for just one or two prisoners only. As a result, verification of these situational and environmental factors is questionable and needs further investigation in larger sample sizes.