We present the prevalence of depression and its correlates in a large community sample of elderly insured by the largest healthcare provider in Mexico City. Results, however, must be interpreted in the light of several limitations. First, perhaps the most important limitation of this study is that we were only able to interview a low fraction of those listed in the selected physician offices, in part as a result of a lack of active update in the patient lists used to identify study participants. Census data indicate that we under-sampled city residents with the oldest ages and higher education. We tried to overcome the problem of sample representativeness by calculating selection probabilities specific by age, gender, and education, and we used them as sample weights in all analyses presented here. Additionally we used bootstrapping techniques, considering the sample design, to obtain more valid estimates of standard errors in all statistical analyses. We believe that these procedures allow us to make valid inferences to the non-institutionalized elderly population insured by IMSS residing in Mexico City.
Second, depression prevalence was determined using the 30-item GDS, a scale that assesses depressive symptoms without regard of the 4-week timeframe included in the DSM-IV standard and that, consequently, is prone to exhibit a relatively high GDS false-positive rate39
. Several validation studies have reported lower GDS specificity than sensitivity values for detecting major depression27–31
. We found that one in eight IMSS insured elderly have depression (21.7% overall). Correcting this figure for the average GDS sensitivity and specificity values reported in the reviewed validation studies, we estimate the prevalence of major depression in our target population at 13.2% (6.4% in men and 16.9% in women). The 30-item GDS prevalence figures by gender were similar to those reported in elderly Hispanics in New Mexico using the 15-item GDS40
. Alegría et al. recently studied the prevalence of mental illness in several Latino groups, and it is interesting that lifetime prevalence of major depression among Mexican immigrants was lower than other Latino groups (11.8%), unfortunately no specific data for older persons were reported41
. Our corrected prevalence figures are similar to those found for persons aged 60 and older in a national community survey in Mexico, using a different screening instrument based on DSM-IV criteria19
Third, we analyzed the independent association among significant depressive symptoms and socio-demographic factors, stressful events, cognitive impairment, health-related quality of life, and healthcare use. Such cross-sectional associations are subject to temporal ambiguity. Our study will follow up over time all identified participants with depression and a randomly selected sample of surveyed persons without initial depression. This will allow us to confirm or discard the cross-sectional associations found.
Fourth, the association between depression in the elderly with health-related quality of life and healthcare use may be confounded by the presence of co-morbidities such as diabetes, hypertension, cancer, and cardiovascular conditions. We controlled for co-morbidities only through the variable “recent severe morbidity,” a composite of recent severe health problems and increasing disability. Chronic diseases diagnosed by a doctor were only measured in 39% of participants, which will be followed up overtime. In this sub-sample, we did similar analyses to those presented for the entire sample and found that the addition of terms for six chronic conditions reduced only slightly (less than 15%) the associations between depression and health-related quality of life and healthcare use presented here.
Acknowledging the above limitations, our study provides important findings that contribute to what is already known about depression in the elderly worldwide. Depression was more frequent in women, and an inverse relationship between education and depression prevalence was observed42,43
. In addition, we found a higher depression prevalence in participants reporting stressful events, as has also been found in other studies32,44,45
Cognitive impairment was also more common among participants with depression than in persons without depression. As mentioned by others46,47
, depression could be a risk factor for cognitive decline and dementia. However, the relationship between depression and dementia could be more complex. Thus, depression could be an early symptom of undiagnosed dementia or share common risk factors with dementia48–49
Depression has an independent negative impact on health-related quality of life3,7–8
. We found lower health-related quality of life in participants with depression, regardless of the presence of recent severe morbidity, than in those without depression or recent severe morbidity. An adjusted SF-36 subscale score indicating impairment among depressed participants without recent severe morbidity was similar to those observed in persons with recent severe morbidity but no depression. The exception was in subscales measuring mental health, where score reductions were higher in the group with depression but no recent severe morbidity.
Both cross-sectional and longitudinal studies have also documented that depression increases healthcare utilization3,12
. We found that participants with depression and no recent severe morbidity showed higher increases in utilization rates, both for any reason and for emotional problems, than to those observed in persons who had recent severe morbidity but no depression. Indeed, depression independently increased utilization rates in a similar fashion in those with and without recent severe morbidity. Additionally, consistent with health services research in other countries3,50
, persons with depression tended to use IMSS family medicine units more frequently than hospitals.
In conclusion, our study provides useful information on the prevalence of depression among older adults and its correlates for the urban population in a developing country. Even in developing countries, the benefits of elderly depression treatment in primary-care units may more than offset its associated costs. Treatment may lower utilization rates and eventually free up resources that could be applied to improving the functional status of older adults, improved care for medical conditions that accompany depression51
, and may even extend life52
. In addition, offering treatment for depression may be instrumental in delaying the onset or slowing down the rate of cognitive decline48
. Therefore, the design and implementation of systematic training of primary-care physicians on the detection and management of elderly patients with depression should be granted high priority in developing countries. Primary care teams, including a depression care manager, primary care doctor, and psychiatrist, seem to have better results than the usual primary physician-centred care14
. Finally, it is also important to continue research in this area and to reinforce primary-level healthcare strategies to confront upcoming challenges.