Background
Hypertension, as one of the most common risk factors for cardiovascular disease, is currently defined as systolic blood pressure ≥ 130 mmHg and/or diastolic blood pressure ≥ 80 mmHg, whether for untreated patients or patients taking antihypertensive drugs [
1‐
3]. It affects more than 1.2 billion people worldwide and has become the most critical and costly public health problem [
4]. Hypertension remains the most potent predictor of mortality, as a global risk factor for death, disability-adjusted life years and life loss years [
5]. Some meta-analyses have shown that hypertension was significantly associated with increased risks of Parkinson's disease, stroke, and other diseases [
6,
7]. Consequently, it is necessary and important to study the risk factors and effective predictors of hypertension to reduce the burden on public health.
Sleeping health is increasingly considered a public health problem. Many people suffer from trouble sleeping such as sleep deprivation, poor sleep quality, and sleep disorders, which seriously affect their health [
8]. Over the years, several studies suggested that trouble sleeping was associated with high rates of hypertension [
9‐
13]. Studies consistently found that sleeping time was a U-shaped associated with elevated blood pressure [
14,
15].
Depression is a mood disorder that leads to a variety of functional physical disorders and loss of interest in daily activities, thereby reducing the quality of life [
16]. Studies have shown that individuals with depression had a higher incidence of hypertension [
17,
18]. In the United States, data from the National Health and Nutrition Examination Survey (NHANES) reported that patients with self-reported hypertension still had a significant 15% reduction in the relative risk of death compared with the group with self-reported hypertension and depression after adjusting for clinically relevant confounding factors [
19].
Therefore, when hypertension and depression or trouble sleeping appear at the same time, two risk combinations may be formed respectively, which highlights the importance of identifying depression or trouble sleeping in subjects with hypertension. Besides, trouble sleeping was associated with an increased psychological risk, such as depression [
20]. There were few studies on the direct relationship between the interaction of these two conditions and hypertension. Thus, the purpose of this study was to obtain relevant data from the NHANES, and to study the interaction between trouble sleeping and depression on hypertension.
Discussion
In the present study, we utilized NHANES 2005–2018 data of the included 30,434 people to study the associations of trouble sleeping and depression with hypertension and their interactions on hypertension. We found that there was a synergistic interaction between trouble sleeping and depression, especially moderate depression, on hypertension.
Our present study observed a significant positive association between trouble sleeping and hypertension in the whole study population after adjustment for age, gender, BMI, race, marital status, education, annual family income, alcohol drinking, smoking history, diabetes, stroke and sleep duration. The association between trouble sleeping and hypertension has been proposed and explored previously. Trouble sleeping includes obstructive sleep apnea (OSA), sleep quality (sleep deprivation, sleep duration and insomnia), and combinations of sleep problems. Studies demonstrated the high incidence of hypertension in patients with OSA [
30], and the blood pressure seemed to be dose-related to OSA [
31]. OSA-related hypertension is usually attributed to increased diastolic blood pressure caused by sympathetic activation, which stimulated the renin angiotensin-aldosterone system to increase vascular resistance and cardiac output, causing hypertension [
32,
33].
Short sleep duration may be representative of sleep disorder, and was significantly associated with hypertension [
34,
35], so we adjusted sleep duration in the multivariate logistic regression model. Previous studies showed that short sleep duration (less than 6 h) had an increased risk of hypertension compared to 7 h in a cross-study analysis of more than 7000 samples [
34], and a meta-analysis by Osamu et al. had similar results [
35]. This may be due to short sleep breaks disrupting circadian rhythm and autonomic balance [
36]. Another hypothesis suggested that sleep deprivation or short sleep duration was the stress state that has been shown to promote salt appetite, and inhibit the excretion of renal salt fluid [
37], and excessive salt intake has been confirmed to be a risk factor for hypertension. Notably, long sleep duration (≥ 10 h) was also considered as a risk factor of hypertension [
34]. Guo et al. also found that long sleep duration was positively associated with hypertension in a systematic review and meta-analysis [
38]. Most studies involving sleep problems have used self-reported data. Compared with healthy people, people with functional limitations due to chronic diseases may spend more time in bed, and it may be mistakenly reported as sleep and cause confusion about health condition. Herein, although sleep duration seemed to be related to the prevalence and incidence of hypertension, most cross-sectional studies to date have failed to demonstrate any causality. Moreover, a large population-based study observed significant associations between hypertension and poor sleep quality based on the Pittsburgh Sleep Quality Index (PSQI) scores in rural China [
39]. Rahim et al. found an association between history of shift work (poor sleep quality) and rates of hypertension in 7,420 Ontario workers aged 35 to 69 years in a 12-year longitudinal cohort study [
40]. Thus, changes in the sleep quality or quantity could lead to loss of blood pressure dipping pattern and increased sympathetic activity at night, and then a continuous increase in sympathetic tone in turn, which could result in hypertension [
41].
Trouble sleeping could exist as a single disease, but generally coexist with physical or mental diseases, and long-term sleep quality decline could cause hypertension, low immunity and psychological disorders [
42]. Xiuli Song et al. indicated that there was a significant association between depression and elevated blood pressure using support vector machine (SVM) [
43]. Two cohort studies found that depression was the risk factor of hypertension [
44,
45], which was consistent with our results that depression was significantly positively associated with hypertension in the fully adjusted model. Prior studies found that people with hypertension often have sleep problems and depression [
46,
47]. In addition, it was uncovered that depression was a trigger for hypertension, and hypertension could easily make depression worse [
48]. Patients with hypertension were prone to anxiety, depression and other adverse emotions due to repeated illness, and these adverse emotions induced the fluctuation of blood pressure in patients, causing a vicious circle [
47,
49]. Therefore, it was of great significance to take reasonable and effective nursing methods to keep the mood cheerful and blood pressure stable in patients with hypertension.
Many studies reported that anxiety, depression, tension and depressive emotions were not only predisposing factors for hypertension, but also important factors affecting the sleep quality of hypertensive patients [
50,
51]. A previous study showed that insomnia was associated with mental and psychosomatic disorders [
41], and pure insomnia and insomnia comorbid with depression had a strong correlation in a longitudinal cohort study [
52]. Additionally, trouble sleeping was a risk factor for people with hypertension. A longitudinal population-based study from 2008 to 2016 identified that insomnia may contribute to the comorbidity of hypertension and depression in the United States [
53]. Herein, we found similar results that there was a synergistic interaction between trouble sleeping and depression on hypertension. In normal circumstances, happiness, emotional stability and life satisfaction were regarded as positive factors for maintaining sleep quality, while lack of happiness, tension, depression and anger in life were regarded as negative factors affecting sleep quality [
50,
51]. The bad mood could easily lead to trouble sleeping, which seriously endangered physical and mental health. Moreover, when subgroup analysis was conducted, we only found this synergistic effect between moderate depression and trouble sleeping on hypertension. This may be because the synergistic effect of moderate depression and trouble sleeping was more significant than that of moderately severe or severe depression and trouble sleeping. Although there was no statistical significance between them, the estimated joint effect of two factors was greater than the independent effect of trouble sleeping and moderately severe/severe depression, respectively. Therefore, it was suggested that clinicians should actively intervene in psychological disorders, especially depressive symptoms, while paying attention to improving the sleep quality of patients in the routine drug treatment of hypertension.
Our research strengths lied in the following aspects. First, we used seven cycles, high-quality, representative data from the NHANES about Americans, which was large and multistage. Second, previous studies showed that trouble sleeping and depression were independent risk factors for hypertension, but few studies indicated an interaction between them on hypertension. Here, we found that the synergistic interaction between trouble sleeping and depression on hypertension. Third, the logistic regression model was adjusted for several potential confounding factors, including demographic, socioeconomic, health and lifestyle information, etc.
Several potential limitations existed in this study. Firstly, the measurement of trouble sleeping in this study was self-reported, it was subjective rather than objective. It was also likely that there was no comprehensive understanding of the participants’ sleep quality, sleep efficiency, sleep duration, etc. Perhaps objective measurement methods for sleep health such as activity scanners and polysomnography were needed to strengthen investigations in this field. Secondly, it was a cross-sectional survey, with compromised accuracy and generalizability, so we could not determine the causal relationship or exclude bidirectional relationships.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.