• substance use
• sleep disturbances
• sleep
• insomnia
• energy drinks
• caffeine
• adult ADHD
• addiction
• substance use disorder

Background:
There has been a great deal of research on the comorbidity between Sleep Disorders and Attention Deficit Hyperactivity Disorder (ADHD). Hoewever, most of the existing data are referred to children and adolescents and only few studies have been conducted in adult samples.
Further, the ongoing trend of using energy and caffeinated beverages to improve cognitive performance is widely spread and well-studied among children and teenagers ADHD, but little is known about adult ADHD (A-ADHD). As a consequence, the use of high-in-caffeine drinks and its impact on sleep patterns and ADHD symptoms are under-researched in special population where the A-ADHD and the use of these beverages are both largely represented, such as military samples.
Methods:
Data were collected from the All Army Study of the Army Study to Assess Risk and Resilience in Service members (unweighted N = 21, 449; weighted N = 674,335; 18–61 years; 13.5% female).
Participants completed the Brief Insomnia Questionnaire to assess for insomnia disorder and a self-administered version of theComposite International Diagnostic Interview Screening Scales to assess for psychiatric disorders and cognitive problems.
For ADHD assessment, soldiers completed a battery of experiential and psychological measures including the six-item Adult ADHD Self-Report Scale Screener (ASRS-S).
Finally, the CIDI Substance Abuse Module, in particular, (CIDI-SAM) was used to evaluate tobacco, alcohol, drug and caffeine usage in the past 30 days. Descriptive statistics were conducted to determine the prevalence rates of insomnia, ADHD and Substance Use Disorder (SUD). Pearson's Chi-square test was used to assess the association between insomnia and ADHD.
Results:
Military soldiers with a diagnosis of ADHD had the highest prevalence of insomnia disorder and all its subtypes, i.e. difficulty initiating sleep (i.e. taking more than 30 minutes to fall asleep at night, p<.0001), difficulty maintaining sleep (i.e.waking up three or more times during a single night, waking up at night and taking more than 30 minutes to get back to sleep, p<.0001), early- morning awakenings with inability to return to sleep (i.e. waking up more than 30 minutes too early in the morning, p<.0001), with negative impact on every ADHD clinical features, affecting both the inattentive and the hyperactive/ impulsive phenotypes. Similarly, significant interactions were found between ADHD and SUD, with the use of tobacco/caffeinated drinks and alcohol being positively correlated to ADHD (p<.0001).
Finally, relevant differences were detected between high-in- caffeine- drink users and non-users, in terms of ADHD symptoms, however affecting only some areas of memory and attention functions, at variable degrees.
Conclusions:
The relationship between insomnia and ADHD seems to continue throughout adulthood, suggesting that sleep disturbances , influencing memory and concentration, may contribute to the persistence of the characteristic cognitive pattern associated with the ADHD.
The use of caffeinated compounds appears to be largely diffused among ADHD military soldiers and it could improve cognitive performance, despite the negative repercussions on sleep.
According to our data,in fact, caffeine may positively influence specific areas of memory and attention, but still the definition of its mechanism and target specificity remains unclear.
Therefore, our results highlight the importance of focusing on insomnia in the diagnosis and treatment of ADHD in military soldiers.
However, further research is necessary to explore a possible role for caffeine as a potential pharmacological tool in the treatment of adult ADHD.