Evidence suggests that the prevalance of depression is elevated in those with chronic illnesses such as diabetes [1, 2]. Current epidemiological evidence suggests that at least one third of people with diabetes suffer from clinically relevant depressive disorders [3–5]. However, in spite of the huge impact of co-morbid depression and diabetes on the individual and its importance as a public health problem, little is known about the existence of psychological problems in people with diabetes in Bangladesh or the Bangladeshi origin immigrant population in the west [6]; a population group who have a markedly increased risk of developing Type 2 diabetes mellitus (T2DM) [6–8]. Although there is a scant literature describing the prevalence of depression in Bangladesh, there is an assumption that the burden of mental disorders on the Bangladeshi population is high [9]. Limited data from South Asian settings have reported two to five-fold increases in the prevalence rates of depression in people with diabetes compared to people without diabetes [9–12]. One of the major challenges in assessing depression rates in South Asian countries is that no depression screening tools have been culturally standardized for these specific populations. Previous research has demonstrated the potential of a range of different modes of data collection in these ethnic groups (where illiteracy rates are high), including audio versions of questionnaires, as well as assisted completion, depending on the type of questionnaire to be completed [13]. Our recent research in the UK has developed culturally specific methods for administering and collecting reliable data on psychological morbidity in South Asian people with T2DM [14]. The present study set out to screen for the prevalence of and factors associated with the risk of depression in a random sample of out-patients with T2DM living in Bangladesh where literacy problems in data collection also arise, using recently developed and culturally standardized Bengali and Sylheti audio versions of the Patient Health Questionnaire-9 (PHQ-9) and the World Health Organization-5 Well-being Questionnaire (WHO-5).

This study examined the prevalence of and factors associated with depression in a random sample of out-patients with T2DM in Bangladesh. To our knowledge, this is the first study that has investigated the prevalence of depression using data collected through two different modes; i.e. standard assisted collection and audio questionnaire methods. We found similar prevalence rates of depressive symptoms regardless of which screening tool was used (PHQ-9 vs. WHO-5), and regardless of the language of the questionnaires (Sylheti vs. Bengali) or the method used (the standard assisted vs. independent audio method).

Our study provides evidence that depression is common in T2DM in Bangladeshi settings. More than one-third of individuals reported poor emotional well-being using the WHO-5 questionnaire and similar prevalence rates of depressive symptoms in patients with T2DM when using the PHQ-9. When using a lower cut-off value for the WHO-5 (score ≤ 28) or a cut-off value for the PHQ-9 (score ≥10) indicative of moderate to severe depression, the prevalence rates of depression were very similar for both questionnaires. These prevalence rates are in the line with recent studies that have used PHQ-9 in the primary care settings [21, 22]. This prevalence of poor wellbeing and depressive affect is also comparable to the results of one recent study in diabetic out-patients that reported poor wellbeing in 35–38% and depressive affect in 18–25% of patients with T2DM [19]. A handful of studies have reported a higher prevalence of depression in people with T2DM compared with those without diabetes or in the general population [23–25]. In a systematic review of cross-sectional prevalence data, Ali et al. [2] also reported significantly higher rates of depression in those with T2DM compared to adults without.

An earlier population-based study in Bangladesh has reported almost similar rates of depressive symptoms (29.7%) in a rural population with diabetes using the Montgomery-Asberg Depression Rating Scale [9]. In that earlier study higher socio-economic status and a high BMI were found to be protective factors against depression. We also observed these links in our current study population in Bangladesh, however this association was no longer significant at the multivariate level when controlling for other demographic and clinical variables.

The earlier study further reported that depression was associated with poverty and the authors assumed that as poverty is more prevalent in rural areas, the prevalence of depression may also be higher [9]. Our sample comprised a mix of urban and rural populations and although we found a similar link between poverty and depression, in fact the opposite association was observed in terms of participants’ area of residence. At the univariate level urban residents with T2DM were nearly twice as likely to be depressed as rural residents when measured using either the PHQ-9 or WHO-5 questionnaires. However, this association no longer persisted after controlling for other confounding factors.

Consistent with the results of other published studies in Bangladesh and elsewhere [2, 9, 23], our results demonstrated a significantly higher prevalence of depression in women with T2DM compared with men with T2DM. After controlling for potential confounding factors, gender remained as the strongest risk factor for depressive symptoms, with nearly a threefold increase risk in females compared with males.

Poor glycaemic control was also a strong predictor of depression in our sample for both multivariate models. This finding is in the line with previous studies [23]. It is known that depression has a negative impact on quality of life and that depression worsens glycaemic control [5, 26]. Numerous studies, overwhelmingly cross-sectional, support our findings and suggest that depression is associated with suboptimal glycaemic control, although in a systematic review the effect size was mild [5]. A recent prospective study demonstrated a clear prospective association between depression at baseline and persistently higher HbA1c levels over a 4 year period [27].

Our findings also suggest that the presence of one or more complications, in particular cardiovascular disease, was significantly associated with depression in patients with T2DM. This finding is in the line with recent studies that show that the risk of depression is significantly associated with the number of diabetes-related complications [21, 28]. Having multiple chronic diseases in addition to diabetes has a high impact on well-being, quality of life and functioning and thus may contribute to further development of depression [29]. It is suggested that patients with severe diabetes-related complications, especially late micro- and macro-vascular complications such as retinopathy, nephropathy, neuropathy or cardiovascular disease, are more likely to be referred to specialized clinics. If these patients are adequately treated, they are more satisfied with their care and overall functioning [28]. Our findings are relevant for clinicians and nurses who work in diabetes outpatient clinics in order to take timely decisions for appropriate referral.

Evidence also suggest that diabetes complications and depression often coexist and the prevalence of depression is particularly increased in those with longer lasting T2DM, but not in undiagnosed T2DM or those with impaired glucose metabolism [30]. A number of studies highlighted that the incidence of depression is increased in T2DM [31, 32] and that depression is a risk factor for T2DM [33]. However, It is important to increase our understanding of the temporal relationship between the development of secondary complications and the onset or recurrence of depression. Future studies should aim to address these issues.

One of the major challenges in measuring depression in Bangladesh is that no depression screening tools have previously been culturally standardized for the population in Bangladesh. Our previous research in the UK has developed culturally specific methods for administering and collecting reliable and valid data on psychological morbidity in South Asian people with T2DM (including Bengali and Sylheti speakers) and has established the face validity and cultural equivalency of two widely used depression screeners (the PHQ-9 and WHO-5) [14]. This research used those culturally standardized tools and demonstrated their utility as potential depression screeners in wider sample like current study population.

A number of studies documented that depression symptomatology is influenced by social and cultural factors [14]. In contrast, this study gives us the impression that the prevalence rates and the risk factors for depression in Bangladesh are very similar to European countries and the US [19, 22, 23, 26]. Thus, it provides a room for argument that even if the meaning of depression varies cross-culturally, its crude prevalence or association to risk factors may not be culture specific.

The findings of this study have major implications for clinical practice in Bangladesh, where physicians’ recognition of mental disorder rates is low and improving recognition rates is a challenge because of the high patient loads and poor undergraduate training in these skills. Providing the patients with the results of blood sugar, cholesterol, blood pressure and medications plan through outpatient service is not enough itself to improve service delivery and bring about change [34]. We need to overcome therapeutic inertia and low diabetes health literacy [35]. There is increasing recognition that patients with diabetes and depression require adequate mental healthcare, however, evidence in favour of routine screening and monitoring is not conducive yet. A few studies have tested whether screening for depression or monitoring of psychological well-being has beneficial effects, but results of these studies are conflicting to come to any conclusion [36–39].

In the developed world (for example in the North America and UK), self management is available for all new cases of diabetes. Undoubtedly, the patients with co-morbid diabetes and depression in Bangladesh would benefit from this approach. In the Bangladeshi settings, the clinician who sees the patients with diabetes could take on the role of initial assessment for depression and coordinate referral to mental health clinic for therapy and onward referral and follow-up with the patients [40].

In conclusion, our study demonstrated that depression is a common co-morbid health problem in T2DM out-patients in Bangladesh, with more than one-third of patients reporting elevated depression scores regardless of depression screeners and data collection methods used. Within this sample of out-patients with diabetes, we found that female gender, older age, low income, treatment with combine insulin and oral medications, poorly controlled T2DM, and those with coexisting complications of diabetes were independent risk factors for depression symptoms.

This study provides rich data on the prevalence and determinants of depression in T2DM outpatients in Bangladesh. In a setting where recognition, screening and treatment levels remain low, health care providers need to focus their efforts on diagnosing, referring and effectively treating this important disease in order to deliver rights-based and client-centred services for people in real needs.