The prevalence of depression in this sample was 10.7%, which is higher than that in the general population. The National Comorbidity Survey Replication reported a prevalence of 6.6% (95% CI = 5.9% to 7.3%), although in that study, depression was assessed using a more detailed questionnaire/interview than the PHQ-9.34
The prevalence of depression was also higher than that in the general population when the sample was split into groups by diabetes status. In this sample, the prevalence of depression in participants with diabetes was 12.8% and was 9.4% in participants without diabetes. In the National Health Interview Survey, the depression prevalence among individuals with diabetes was 9.3% and was 6.1% among individuals without diabetes.35
As in the general United States population, the prevalence of depression was also higher among women than among men in our sample.36
There have been few previous reports directly assessing the prevalence of depression among American Indians.37
In the American Indian Service Utilization, Psychiatric Epidemiology, Risk and Protective Factors Project (AI-SUPERPFP), a population-based study of 3084 tribal members from 2 American Indian reservations, the prevalence of any episode of depression occurring during the previous 12 months was 2.8% among men and 4.9% among women.38
The prevalence of depression in the current report was higher among both men (7.5%) and women (12.8%). However, it is difficult to directly compare the results reported here with those in the AI-SUPERPFP because that study used a more detailed questionnaire for assessing depression and a different time frame (i.e., 12 months) than in the current report (the last 2 weeks). A recent study of the elderly with diabetes compared the prevalence of depression among American Indian, white, and African American participants using the Center for Epidemiologic Studies Depression Scale (CES-D) to assess depressive symptoms. While this study reported that the 181 American Indian participants had a higher prevalence of depressive symptoms (21%) than either of the other 2 racial groups, this difference was not statistically significant.39
Since this study only included participants with diabetes, these data are difficult to compare with other estimates of depression prevalence in American Indians. The current report, on the other hand, presents data on the prevalence of depression in American Indians with and without diabetes.
In the pilot phase of the current study,29
we found that the overall prevalence of depression was 16.3%, which is higher than the prevalence of depression reported here. This difference is most likely due to the different modes of administration of the questionnaire: in the pilot phase of the study, depression was assessed using a face-to-face interview tool (PRIME-MD), while in this report depression was assessed using a self-administered paper version of the same questionnaire (PHQ-9). In other studies, estimates of the prevalence of depression differed based on the mode of screening (interview versus self-administered), although usually, interview methods yielded lower estimates of depression prevalence than self-administered approaches.40
In the absence of a “gold standard” measure for depression, we are unable to say whether in this population the presence of depression was overestimated with the interview questionnaire, underestimated by the self-administered questionnaire, or whether the difference is explained by some unmeasured difference between the subjects included in the pilot study and those included in the current report. Pima Indian clinic staff who were presented with this finding suggested that because a segment of the study participants may have limited literacy, those individuals may have had greater comprehension of the questions when asked about depression symptoms in an oral interview. We attempted to minimize problems with literacy by selecting a questionnaire that uses simple language and by orally administering the questionnaire to those participants who requested assistance. However, literacy was not directly assessed in the study, and so we cannot draw any direct conclusions about the impact of literacy on the self-reported prevalence of depression. Clinic staff also suggested that concerns about confidentiality may have caused some research participants to be reluctant to admit to depression symptoms on a written questionnaire that they were filling out in a public waiting room, while participants may have been more willing to do so when interviewed in a private room. It was not possible to directly compare the different methods of depression assessment because there was no overlap between the 2 study phases. Further studies, perhaps using ethnographic methods, may be necessary to fully elucidate the reasons that interview screening yielded a higher prevalence estimate of depression in this population than a self-administered questionnaire.
Although a few clinical trials have assessed the efficacy of antidepressant medications in individuals with diabetes,41–45
few cross-sectional reports on diabetes and depression have assessed the use of antidepressant medications. The prevalence of reported antidepressant medication in this sample was 5.0%, and there was little overlap between the group of participants with depression by PHQ-9 score and those taking antidepressants. Similar results were reported by the Diabetes Prevention Program.46
Diabetes and depression were significantly associated in women but not men, although there was not a significant sex interaction in this association. Due to the smaller numbers of depressed men (i.e., lower prevalence of depression in men than in women), the confidence interval around the odds ratio for the association of diabetes and depression is wide, consistent with the same degree of association as seen in women. Thus, this study is inconclusive regarding the association of diabetes and depression in men. Many previous reports have shown a higher prevalence of depression among individuals with diabetes.13,5,6
However, there have been few studies of depression and diabetes in nonwhite populations.15
It is possible that the relationship between depression and diabetes may vary by ethnicity: 3 studies in Hispanic populations and 1 in a multiethnic sample also did not find an association between depression and diabetes.16–19
Consistent with the results reported here, diabetes was not associated with a current diagnosis of depression among American Indians in the AI-SUPERPFP study, although there was a significant association between a past diagnosis of depression and diabetes.24
In a study of cognitive function and type 2 diabetes in elderly American Indians, those with diabetes had a slightly higher score on the CES-D scale than those without diabetes (17.2 ± 0.5 vs. 15.9 ± 0.4, p = .04).47
Diabetes is much more prevalent in our sample than in the general U.S. population.27
The high prevalence of diabetes could make the psychosocial impact of the disease different in this community than in the general U.S. population. The lack of a statistically significant association between depression and diabetes in this sample also may indicate that certain social, cultural, or economic factors overshadow the association between depression and diabetes in this population. We cannot account for factors that might engender reactive depression, such as income and education, as these data were not collected. We also do not have data on eating habits or dietary interventions, but did find that for participants with both depression and diabetes, there was a greater use of both oral hypoglycemic agents and insulin than there was for participants with diabetes who were not depressed. This finding is expected, in light of the poorer glycemic control in the depressed subjects with diabetes.
In addition to the difference in ethnicity between our study population and participants included in most previous studies of depression and diabetes, our study also has methodological strengths compared with other reports. We assessed diabetes using an oral glucose tolerance test, whereas the majority of previous studies have used self-report methods1,3,7,18,24
or diagnostic codes in health insurance databases5,6
for diagnosis of diabetes. We also assessed depression symptoms directly using a screening questionnaire based on DSM-IV diagnostic criteria rather than relying on diagnostic codes in the medical record5,6
or self-report of depression diagnosis or treatment.3
Although depression and diabetes were significantly associated only among women in this study, HbA1c
was significantly higher overall in individuals with diabetes who were depressed than in those who were not. These results are consistent with those reported in the pilot phase of this study.29
This report not only provides further evidence that depression is associated with poor glycemic control, but also shows that the severity of depression (as measured by depression score, which is determined by number of depression symptoms and how often they are experienced) is positively correlated with HbA1c
. Although the PHQ-9 was devised as a screening tool for depression, previous studies have shown that higher scores are associated with more severe levels of depression, so we feel justified in using it here as a continuous measure.30
In addition, fasting plasma glucose and serum triglyceride concentrations were also higher in depressed individuals with diabetes. In individuals without diabetes, fasting plasma glucose was lower in depressed men than in those without depression, although there were no other significant associations between depression and measures of lipids or glycemia. In contrast to our findings, there was no relationship between depressive symptoms and HbA1c
in a study of elderly people with diabetes including American Indians.39
This may reflect the older age of those study participants (all were ≥ 65 years of age), the better glycemic control in that sample (mean HbA1c
= 6.8%), and the use of a different tool for assessing depression.
In the current report, cigarette smoking was also associated with depression among participants without diabetes, consistent with the association between cigarette smoking and depression reported for the general U.S. population.48
Therefore, the results reported here provide evidence that depression is associated with poor glycemic control in American Indians with diabetes across a wide age range. The AI-SUPERPFP, which is the other recent study to examine the relationship between depression and diabetes in American Indians, did not examine the association of depression with metabolic risk factors.24
Our study indicates that identification and treatment of depression may be important in managing diabetes in American Indians.
The causes of the association between depression and hyperglycemia in individuals with diabetes cannot be determined from this cross-sectional study. On the one hand, it is possible that plasma glucose, HbA1c
, triglycerides, and total cholesterol are higher among depressed participants with diabetes in this sample because individuals who are depressed may have poor adherence to prescribed diabetes treatment or self-care (diet, exercise, seeking health care) regimens.49,30
Depression, anxietsy, and other psychiatric disorders can hinder patients from successfully managing their diabetes.51–53
In this study, more participants with diabetes and depression were prescribed oral hypoglycemics and insulin than the nondepressed participants with diabetes. On the other hand, poor glycemic control or dyslipidemia could adversely affect the psychological well-being and quality of life of individuals with diabetes.54,55
Managing diabetes is stressful for many patients, and it is possible that patients experience depression in reaction to being diagnosed with diabetes or hyperglycemia.55
Finally, depression and hyperglycemia might act in a vicious cycle whereby depression worsens glycemic control, and poor glycemic control, in turn, results in mental distress.2
One study has shown that treatment of depression with either medication or counseling improves glycemic control in patients with diabetes, at least in the short term,41
although in studies with longer follow-up (12 months), results have been mixed.43–45
The long-term effects of treatment with antidepressant medication on glycemic control are not known.42–56
That there was no association between glycemia and depression among participants without diabetes in the current report is not surprising, particularly for HbA1c
, which has such a limited range among participants without diabetes. However, HbA1c
in individuals without diabetes is clinically important because it predicts mortality.57
If depression is indeed a risk factor for development of diabetes, we might have expected to see higher glucose levels associated with more depression symptoms in the participants without diabetes.
Pima Indians with diabetes in this sample had a slightly higher prevalence of depression than those without diabetes, although this association was statistically significant only in women. In those with diabetes, depression was associated with elevated HbA1c
levels. This study adds to the sparse literature on depression and diabetes in American Indians. Previous studies in other populations have shown that depression is associated with hyperglycemia. We have confirmed that depression and hyperglycemia are also associated in American Indians, an ethnic minority group with a high prevalence of diabetes. Further studies are necessary to determine the precise mechanism(s) by which depression is associated with hyperglycemia and dyslipidemia. Among people with depression and diabetes, members of ethnic minority groups are less likely to be treated for depression.19,20,23
This finding is of concern because ethnic minority groups such as the Pima Indians have a high prevalence of diabetes as well as depression, and depression treatment may improve glycemic control.41
Further investigation is needed into whether treating depression in patients with diabetes improves glycemic control and the risk for later complications of diabetes, especially in American Indians and other ethnic minority groups.