Original articleThe role of depression and anxiety in onset of diabetes in a large population-based study
Introduction
The prevalence of depression among patients with diabetes is higher than in the general population [1], [2]. The odds of depression have been estimated to be twice that of the nondiabetic population [1]. There has been less focus on anxiety in patients with diabetes, yet a meta-analysis [3] showed increased prevalence of symptoms of anxiety and generalised anxiety disorders.
The reasons for higher prevalence rates of depression and anxiety are not fully understood. There are two hypotheses about possible relationships [4]. The first regards mood disturbance as being manifestations of direct physiological effects of diabetes. The second hypothesis sees mental symptoms as stemming from the stresses and strains of having a chronic somatic condition. Recently, some studies suggest depression precedes diabetes and increases the risk of developing type 2 diabetes [5], [6], [7], [8], [9], [10], [11], [12], [13]. These findings are consistent with research outside the field of diabetes, which has shown that depression and anxiety predict subsequent morbidity [14], [15].
In prior research, which mainly has been cross-sectional, mental symptoms have been considered a consequence of diabetes, yet the association between diabetes and subsequent development of depression or anxiety has not been explored in longitudinal perspectives.
One study has investigated if depression or anxiety may predict type 1 diabetes and found no such associations [16]. Nine studies with population-based longitudinal data suggest that depression predict the onset of type 2 diabetes [5], [6], [7], [8], [9], [10], [11], [12], [13]. Two studies did not find any relations [16], [17]. The majority of these studies relied on self-reported measures to identify mental symptoms and diabetes. Some of the studies involved rather homogenous samples [6], [10], [12], and some included small sample sizes [5], [6], [9], [10], which may have limited the generalisability. Only one of these studies investigated a number of metabolic factors as possible mediators in the development of type 2 diabetes [8].
The mechanisms that underlie the associations between depression and onset of type 2 diabetes are unclear. Symptoms of depression may predict diabetes independently or through established risk factors for diabetes. Lifestyle factors, metabolic factors, and neuroendocrinological factors have been linked to increased risks of developing diabetes in individuals with depressive symptoms. Possible mechanisms include the influence of depressive symptoms on behavioural factors, such as sedentary lifestyles, smoking, and overeating, resulting in metabolic disturbances, which may explain the onset of diabetes. Altered activities in the hypothalamic–pituitary–adrenal (HPA) axis with cortisol elevations during depressive episodes, which affect approximately half of all patients [18], may also increase the risk of type 2 diabetes.
More population-based studies are needed to establish a temporal relationship between depression and types 1 and 2 diabetes, as well as possible mechanisms to explain the connections [19]. The aims of this study are, first, to investigate if symptoms of depression and anxiety predict onset of diabetes or vice versa and, second, to explore whether the potential links are mediated by risk factors related to diabetes or symptoms of depression and anxiety.
Section snippets
Study population
This investigation draws data from two large health studies in Norway, HUNT-1 and HUNT-2 (Nord-Trøndelag Health Studies, www.hunt.ntnu.no). All inhabitants of Nord-Trøndelag County aged 20 years and above received invitations to participate in the first and second health study. Of the total population in the county, 74,997 individuals attended HUNT-1 in 1984–1986 (88.1%) and 65,648 individuals attended HUNT-2 in 1995–1997 (71.3%).
In HUNT-1, blood pressure, height, and weight were measured, and
Results
Table 1 shows the sociodemographic, lifestyle, metabolic, and clinical characteristics at follow-up of the 37,291 individuals who participated in both health surveys. A total of 8311 (22.3%) had symptoms of depression and anxiety (ADI) at baseline. Among those with a positive ADI, the prevalence of newly developed type 2 diabetes (2.5%) was significantly higher over the 10-year follow-up as compared to the prevalence among those without symptoms of anxiety and depression (1.6%) (P<.001).
Discussion
This study had three major findings. First, we did not find increased risk for developing depression or anxiety in those who reported diabetes at baseline. Second, symptoms of anxiety and depression were associated with onset of type 2 diabetes, but not type 1 diabetes. There were no gender differences. Finally, the analyses did not reveal underlying factors that mediated the association between symptoms of depression and anxiety and subsequent type 2 diabetes.
Depression is prevalent in
Acknowledgments
Nord-Trøndelag Health Study (The HUNT Study) is a collaboration between HUNT Research Centre, Faculty of Medicine, Norwegian University of Science and Technology (NTNU, Verdal), Norwegian Institute of Public Health, and Nord-Trøndelag County Council.
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