In the present study, we identified depression and use of antihypertensive drugs were independently associated with HRQoL. We also found that compared with sleep duration of 7-8h, sleeping < 7h was associated with a significantly lower HRQoL, while sleep duration ≥ 8h did not show a significant difference. It might suggest that a longer sleep duration might not improve the quality of life in individuals with type 2 diabetes.
HRQoL has gained more attention as an essential health outcome indicator in chronic diseases[16]. A list of determinants of HRQoL includes country, social-economic class, and scoring methods, et al. Therefore, the country-specific scoring algorithms were developed to calculate EQ-5D-5L index score, a standardized generic instrument for estimation of HRQoL. To date, a few studies explored the possible factors associated with HRQoL in participants with type 2 diabetes in China. Reportedly, age and chronic complications of participants with type 2 diabetes had inverse correlations with the EQ-5D scores, while clinical factors, including glycemic control, lipids, hypertension, showed minimal associations[17] [18]. Furthermore, we found in the present study that use of antihypertensive drugs is an independent factor of EQ-5D-5L index score and EQ-VAS. HRQoL is an important predictor of mortality and morbidity, further studies are warranted to improve life quality and prolong life span of individuals with type 2 diabetes in China.
Depression is a common mood disorder and affects individuals with diabetes. A published meta-analysis reported a double odd of depression among individuals with diabetes[19]. Till now, the prevalence of depression in individuals with type 2 diabetes has been reported with great variations among different studies in China. For example, Zhang, et. al. reported [20] a depression prevalence of 5.7 % among the hospitalized participants with type 2 diabetes in which depression was defined as Beck Depression Inventory scores ≥ 14. Another research from Hong Kong using the Geriatric Depression Scale showed that 26% of individuals with diabetes aged 60 years or older had elevated levels of depressive symptoms [21]. Our study reported that 8.9% of a community-based population of participants with type 2 diabetes had at least mild depression with the cutoff of PHQ-9 scores ≥ 5. These discrepancies probably accounted for study design, demographic characteristics, time frame, and measurement tools [20–23]. A further nationwide epidemiological survey is required for validation of the prevalence of depression among individuals with type 2 diabetes in China.
Extensive research has identified the risk factors of depression in individuals with type 2 diabetes. In the present study, individuals with depression had higher educational levels and more usage of lipid-lowering drugs. Similarly, Yu S, et al. found that sleep duration was significantly associated with depressive symptoms in individuals with diabetes, in particular those with higher education levels. The positive association between lipid-lowering drug use and depression was consistent with other human studies as well as animal studies [24, 25]. A mendelian randomization study found an increased risk of depression during statin and proportion convertase subtilisin/kexin type 9 inhibitor therapy [25]. One possible mechanism lied on the deregulations in serotonin neurotransmission results from the perturbed cholesterol metabolism [26]. The other documented variables significantly were associated with depression syndrome in individuals with diabetes did not show significant associations in the present study, such as glycemic control and gender [20, 27]. The low prevalence of depression and the mild depression symptoms might affect the statistical power.
More likely to be neglected by health care providers, sleep disturbance was often accompanied by depression, such as longer sleep latency, increased awakenings, and earlier waking compared with non-depressed individuals [28]. Thus, sleep duration might be a factor associated with HRQoL in type 2 diabetes. In our study, sleep duration was significantly associated with HRQoL in individuals with type 2 diabetes. Further, sleep duration of 7-8h was associated with a higher quality of life compared with sleep duration < 7h. However, a longer duration equal to or more than 8h does not mean a better quality of life, consistent with that in the general population [29]. Also, involvement of depression, sleep duration, and other clinical factors in multiple stepwise regression analysis found the association between sleep duration and quality of life was attenuated. That means depression might act as a confounder in the association between sleep and quality of life.
This study had several limitations. First, the study was cross-sectional, limiting the causality. Longitudinal research could draw a more confirmative conclusion. Second, the “gold standard” for diagnosis of depression in clinical practice is a clinical interview for the Structured Clinical Interview for DSM-IV Axis I Disorders. However, it is difficult to use in epidemiological studies with thousands of participants. Thus, PHQ-9 was one of the most often used international measurement tools with high sensitivity and specificity.
In summary, the results of the current study demonstrate that depression was inversely associated with health-related quality of life in community-based individuals with type 2 diabetes in China. Individuals with shorter sleep duration (< 7h) are prone to having depression and those with sleep duration of 7-8h have a better health-life quality. Our results suggest that it is important to identify individuals with type 2 diabetes with depression and shorter sleeping hours in the clinical treatments.