4 | DISCUSSION
The main finding of our study was that sleep dissatisfaction, short sleep, and asthma were all associated with an increased risk of suicidal ideation. However, long WCUS was associated with a decreased risk of suicidal ideation in Korean adolescents with asthma. To the best of our knowledge, this is the first study to investigate the relationship between WCUS and suicidal ideation in adolescents with asthma after adjusting for multiple potential confounding factors.
Our results indicate that short sleep duration is significantly associated with suicidal ideation in adolescents with asthma. Approximately 8-10 hours and 7-9 hours of sleep are considered sufficient for teenagers and young adults, respectively.20 In general, adolescents are considered to be chronically sleep deprived with decreased total sleep duration and increased daytime sleepiness.12 This chronic sleep deprivation is due to a variety of factors including decreased parental control, inconsistent bedtimes, increased schoolwork, poor sleep hygiene (e.g., caffeine use late in the day, technology in the bedroom, smartphone overuse), and a discordance between biological circadian rhythms and early school start times.12 In Korea, most middle- and high-school classes start before 8:30 AM. And many Korean adolescents attend private academic institutions and study late at night even on the weekends.15 These students face strong psychosocial pressure to attain sufficient grades for admission into prestigious universities.7,15 The link between short sleep duration and suicidal ideation in adolescents with asthma is complex and not fully understood. However, there are several possible explanations for this association.
First, sleep deprivation itself is considered to be a stress-inducing factor for adolescents with a higher risk of several mental disorders such as behavioral disorders,22 substance abuse,22 depression,22,23 and suicidality.22 In adolescents with asthma who have sleep problems commonly, including prolonged sleep onset latency, difficulty in falling asleep, frequent nocturnal awakenings, daytime sleepiness, and early awakenings,24 even when their asthma symptoms are well controlled,12 short sleep duration may be associated with higher risk of suicidal ideation
In addition, given its long-term disease course, asthma is associated with depression due to the need for chronic treatment and the repeated exacerbations that may themselves cause hopelessness.25 The chronic nature of this disease may lead to increased asthma symptoms through risk-taking behaviors (smoking, drinking, non-adherence to medication and poor illness control in general)25 and consequently increased suicide risk.26,27 As it is known that people with asthma have a significantly increased risk of suicidal ideation,28suicidal ideation may become more prevalent in adolescents with asthma when they become sleep deprived.
Third, in patients with asthma, the prevalence of obstructive sleep apnea (OSA) and sleep disordered breathing (SBD) is consistently higher than it is in the population without asthma.24,29,30Asthma seems to be a consistent and independent risk factor for SDB (OR = 1.9 [1.69-2.18]).29 Gutierrez et al. found that maximal percentage of rapid eye movement (REM) SpO2desaturation, and the REM obstructive apnea–hypopnea index (OAHI) were significantly higher in asthmatic children with OSA than they were in subjects with OSA alone.31 These findings may result in sleep deprivation in adolescents with asthma, and then may be associated with a high risk of suicidal ideation related to the aforementioned negative mental health state in asthma.
Another notable finding in our study was that adolescents with asthma were more likely to be night owls on both weekdays and weekends, while be early larks only on weekdays. As we hypothesized, adolescents with asthma had shorter weekday sleep duration and longer weekend sleep duration than did those without asthma. These findings may be explained by the sleep characteristics and problems of asthma itself, including nocturnal symptoms and the aforementioned educational uniqueness in Korea. These differences may also be related to the longer WCUS in adolescents with asthma than that of those without asthma for sleep debt compensation. Because individual sleep needs vary, WCUS is not only an indicator of the degree of insufficient weekday sleep,5 but also is a compensatory behavior to cope with weekday sleep debt.32 A recent study found that the risk for anxiety and depression was higher among adults who did not have WCUS than it was among those who did.32 Long WCUS was associated with a decreased frequency of asthma and depression in Korean adolescents.5,15 However, it is unclear whether WCUS has advantageous effects on emotional states of adolescents with asthma, because sleep hygiene guidelines recommend regularizing sleep time and wake-up time15,20 In particular, the association between suicidal ideation and WCUS in adolescents with asthma has not been evaluated previously . To the best of our knowledge, our results are the first to show that sufficient WCUS duration (of ≥2hr) may play a protective role against suicidal ideation among adolescents with asthma. However, this finding does not mean that adolescents with asthma should sleep longer on the weekends than they do during weekdays. Nevertheless, it is important for adolescents with asthma to achieve sufficient sleep time during the weekend in the way that WCUS is an indicator of insufficient weekday sleep.
There are several methodological limitations in this study that must be noted. First, our results are subject to recall bias, because we used self-reported data collected via the internet. Studies using more objective assessments of sleep, such as polysomnography or actigraphy, are needed to avoid this limitation. Second, we only collected data at a single point in time by asking about typical sleep pattern over the preceding week. Weekend sleep duration may vary depending on the situation of the following week (e.g. school examination). Longitudinal studies are needed to clarify our findings, as asthma control and sleep patterns may change throughout the school year. Third, this study was cross-sectional in design; therefore, we were unable to establish a causal relationship between associated sleep factors and suicidal ideation in adolescents with asthma. Well-controlled prospective studies are necessary to confirm the results of the present study. Fourth, we did not analyze asthma management, treatment modalities, or asthma severity because such information was lack and only the lifelong diagnosis of asthma was evaluated in the survey. This omission may have led to the misclassification of asthma. In addition, despite adjusting for various potential confounders, the survey did not assess other significant factors that have been associated with poor sleep quality, such as OSA, snoring, nocturnal gastroesophageal reflux, internet or smartphone use time, and caffeine or drug use.
Despite these limitations, this study also has several strengths and important clinical implications for adolescents with both asthma and sleep problems. This was a nationwide, government-directed survey with a high response rate (96.2%). To the best of our knowledge, our study included the largest number of participants among similar studies. A socioeconomically diverse sample with an equal proportion of middle school and high school students (400 schools each annually) were represented. All of the analyses in this study were based on sample weights and were adjusted for the complex sample design of the survey. Almost all participants had the same ethnic background, which minimizes other possible confounding factors. These study characteristics also mean that our results are generalizable to the overall Korean population. Most of all, this research was the first to identify associated sleep factors associated with suicidal ideation in adolescents with asthma. No prior study had evaluated the relationship between WCUS and asthma. The public health implications of our findings can be applied at the educational and practical levels. A recent study demonstrated that adolescents were able to successfully extend sleep duration with sleep hygiene education.33 This simple intervention would likely be beneficial for adolescents with asthma.12 From an educational perspective, strategic interventions to reduce academic stress on Korean adolescents should be seriously considered, such as a more late start to classes. Health care professionals, including pediatric allergists, require a greater awareness of the risk of mental health problems and suicidality in adolescents with asthma. This is particularly true in those with concurrent sleep problems. When treating adolescents with asthma, these patients require a holistic approach with a more accurate assessment of associated sleep factors related to suicidality.