In this study, we investigated the sleep health status among adults in Gangwon Province by examining the relationship between sleep duration, sleep quality, and socioeconomic state. This study also sought to identify demographic characteristics and lifestyle factors associated with sleep duration and sleep quality.
In this study, indexes of socioeconomic status, such as income level and education level, are associated with sleep quality. The association between socioeconomic status and sleep quality aligns with previous reports.[25–30]
The level of education and sleep duration had a significant association in this study. Otherwise, the association between level of income and sleep duration had no meaningful relationship except only the 3rd quintile income range. Previous studies reported the relationship between socioeconomic state and sleep duration somewhat differently depending on each study.[8, 31] Sleep duration varies by the subject's age, past and present, and race/ethnicity.[32] These different associations between socioeconomic state and sleep duration may be due to a discrepancy in sleep duration in previous reports.
In a previous study, BMI among Korean adults was the main factor associated with sleep quality.[3, 4] The group population may be biased toward a specific group due to certain socioeconomic variables, such as relatively high income and education level, as shown through a study of Samsung executives and employees in metropolitan areas including Seoul. This relationship between BMI and sleep characteristics is consistent with previous study results indicating the association between obesity, poor sleep quality, and long sleep duration among college students.[33]
Unlike previous studies,[4, 34] obesity (BMI ≥ 30) was not associated with poor sleep quality and long or short sleep duration in the present study. Some study have reported no relationship between BMI and poor sleep quality.[35] In addition, in the case of senile people, there is also no relationship between BMI and poor sleep quality.[36] Likewise, the correlation between sleep duration and BMI tends to vary depending on age.[37] Short sleep duration is associated with high BMI, but only among adolescents and young adults. The correlation between sleep duration and BMI is weakened in the above middle-aged group. And, no significant linear relationship is detected in senile people. This may be because the average age of the study participants (57.5 ± 10.6 years) was higher than the average age of the population (39.7 ± 7.1 years) recruited in other studies.
These findings have significant implications for establishing community healthcare policies. These results suggest that although the gap in medical institutions should be addressed, securing a certain level of income or quality jobs is also a fundamental issue in public health.
Similar to previous studies on sleep quality, the present study showed that women had poor sleep quality, which was significantly influenced by subjective stress levels, depression, and sleep health. These results align with those of previous studies on sleep quality and duration.[3, 7] The association between sleep quality and depression was more robust than the association between sleep quality and diabetes mellitus and sleep quality and hypertension, respectively.
Based on previous epidemiological studies,[38, 39] the presence of hypertension and diabetes mellitus is known to be associated with poor sleep quality. Compared with healthy controls, patients with hypertension or diabetes demonstrated objectively decreased sleep efficiency through polysomnography.[40] In this study, diabetes mellitus affects poor sleep quality differently than hypertension. Diabetes-related complications may be accompanied by secondary symptoms that affect sleep disturbance, such as polyneuropathy, restless leg syndrome, nocturia, and hypoglycemia during night.[41]
This study has some limitations. First, the community health survey questionnaire did not include information on circadian rhythm. Therefore, the status of the circadian rhythm could not be reflected in the analysis. For instance, part-time jobs and nightshift and shift works heavily affects sleep health causes excessive daytime drowsiness.[42, 43] Sleep duration did not adequately reflect these aspects; therefore, sleep quality was evaluated as an auxiliary indicator. In this study, irregular eating habits and lack of physical exercise were associated with poor sleep quality. Considering these findings, the relationship between income level and circadian rhythm is assumed to be significant. We propose including a questionnaire that can measure circadian rhythm in future community health surveys.
Second, there needed to be a comparison between the Yeongdong (East side) and Yeongseo (West side) regions. The geographical characteristics of Gangwon Province are divided into Yeongdong and Yeongseo regions around the Taebaek Mountains, and the climates of each region are different. While the Yeongseo area has frequent exchanges with the metropolitan area, especially with Wonju and Chuncheon, the Yeongdong area is relatively more secluded due to poor transportation accessibility to the metropolitan area and geographical factors. Without considering the unique geographical characteristics of Gangwon province, the present study compared rural and urban residence to evaluate the effect of deviations according to administrative districts. Although low compared with metropolitan areas, a gap between the urban and rural areas in Gangwon Province was observed.
Finally, cross-sectional studies cannot determine the temporal sequence of a relationship. Thus, the direction of causality remains unclear, and reverse causation may be possible.