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Lancet. Author manuscript; available in PMC 2010 June 3.
Published in final edited form as:
PMCID: PMC2880490
EMSID: UKMS28655

EPIDEMIOLOGY OF MAJOR DEPRESSIVE DISORDER IN THE IBADAN STUDY OF AGEING

Abstract

BACKGROUND:

The growing elderly populations in Sub-Sahara Africa are exposed to social changes with potential adverse effects on health. To our knowledge, no study has examined the occurrence and impact of major depressive disorder in a large and representative community sample of elderly Africans.

METHODS:

Face-to-face interviews with a representative sample of persons aged 65 years and over (n = 2152) derived through a multi-stage stratified sampling of households in the Yoruba-speaking areas of Nigeria (representing about 22% of the national population). Major depressive disorder (MDD) was assessed using the World Health Organization's Composite International Diagnostic Interview and diagnosed with the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV).

FINDINGS:

Lifetime and 12-month prevalence estimates of DSM-IV MDD were 26 .2 (95% confidence interval, 24.3 – 28.2) and 7.1 % (95% confidence interval, 5.9 – 8.3) respectively. Female gender and increasing levels of urbanization of residence were associated with MDD. Persons with MDD had impaired quality of life and functioning in home, work, and social roles. Independent ratings of symptom severity confirmed presence of clinically significant depression in 96.9% of those with diagnosis and increasing symptom severity was associated with greater disability and poorer quality of life. Only about 37% of lifetime cases had received any treatment and there was a mean delay of 5 years from onset to receipt of first treatment. Low economic status and rural residence predicted lack of treatment.

INTERPRETATION:

MDD is common among elderly Nigerians and its occurrence is related to urbanization. MDD is a seriously disabling illness in this group but only a minority of its sufferers has ever received any treatment.

INTRODUCTION

Studies conducted in Western Europe and North America suggest that depression is a common and often debilitating illness in old age. Its occurrence is associated with functional impairment, decreased quality of life and increased mortality. Projected to become the second most common cause of disability by 20201, depression is now regarded as a major public health concern 2. Little is known about the occurrence and impact of depression among the elderly in sub-Saharan Africa. Indeed, even though the growth in the proportion of elderly persons in African populations is among the fastest in the world, 3, the health of elderly persons living in Africa has received little research attention

Depression among the elderly often has strong social origins. Many studies, mostly conducted in Western Europe and North America, suggest that depression in older persons is associated with low socioeconomic status, low social support as well as poor physical health4,5. Such social factors are indeed also common in many countries in Africa. Nigeria, the most populous country in Africa, provides an example of a place where social changes of potential deleterious effect on the lives of elderly persons are on-going. Rich in land and mineral resources, the country is nevertheless among the poorest countries in world. Its rate of urban growth is among the fastest in the world 6. Many of its cities are characterized by squalor and tough daily existence. Unemployment is over 40% and urban migration is the norm for young educated persons looking for a better life. The country's health service is poor 7 and access to persons with mental illness is particularly limited with only about 10% of those with such illness receiving any form of treatment 8. However, given that life expectancy in Nigeria is currently about 48 years for men and 50 years for women,9 it is probable that persons who survive to the age of 65 years and older may represent a constitutionally resilient subgroup. For example, although the healthy life expectancy at birth in the country is 41 years for men and 42 years for women, men and women who live till the age of 60 years can expect to have another 9 and 10 years, respectively, of healthy life expectancy9.

In this paper, drawing on data from the first large community-based study of its type in sub-Saharan Africa, we present estimates of the prevalence of major depressive disorder (MDD) among persons aged 65 years and over living in the Yoruba-speaking parts of Nigeria. We report on the impact of MDD on role functioning and quality of life and on the correlates of receipt of treatment.

METHODS

Sample

The Ibadan Study of Aging (ISA) is a community based survey of the mental and physical health status as well as the functioning and disability of elderly persons (aged 65 years and over) residing in the Yoruba-speaking areas of Nigeria, consisting of eight contiguous states in the south-western and north-central regions (Lagos, Ogun, Osun, Oyo, Ondo, Ekiti, Kogi and Kwara). These states account for about 22% of the Nigerian population (approximately, 25 million people). The survey was conducted between November 2003 and August 2004.

Respondents were selected using a multi-stage stratified area probability sampling of households. In households with more than one eligible person (aged 65 years and fluent in the language of the study, Yoruba), the Kish table selection method was used to select one respondent10.. Whenever necessary, age eligibility was determined using a previously validated list of historical events. Respondents were informed about the study, invited to participate, but also assured of their right to decline. Participants were those who provided consent, mostly verbal, either because of illiteracy or by choice, or signed, before interviews were conducted. On the basis of this selection procedure, face-to face interviews were carried out on 2152 respondents, giving a response rate of 74.2%. Non-response was predominantly due to non-availability after repeated visits (14%), interviewers unable to trace the original address (4%), death (3%), and physical incapacitation (2%) and rarely due to refusal (2%).

The survey was approved by the University of Ibadan/University College Hospital, Ibadan Joint Ethical Review Board.

Measures

Diagnostic Assessment

Depression was assessed using the World Mental Health Survey version of the WHO Composite International Diagnostic Interview (WMH-CIDI), a fully structured diagnostic interview11. Diagnosis was based on the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) 12. DSM-IV organic exclusion rules were imposed in making the diagnosis of depression. Judgements about which organic conditions could explain a co-occurring MDD was made during clinical reviews (by a psychiatrist) of all questionnaires in which endorsements of depression features were made. We excluded from the analysis all persons with probable dementia diagnosed using a cognitive screen that has been previously validated in our setting 13, The WMH-CIDI is a more user-friendly version with simplified probes and structure. Diagnosis was derived using the same algorithm as in our earlier study in which the WMH-CIDI was used.14 MDD is as an episode of illness, lasting at least two weeks, characterized by, among other features, depressed mood, markedly diminished interest or pleasure, change in appetite and weight, change in quantity of sleep, fatigue, and morbid thoughts. Diagnosis is made when symptoms cause significant distress or impairment and they are not better accounted for by a medical condition, medication, or by bereavement. Even though MDD is not the only form of depression, dysthymia and minor depression being other examples, it is the most severe. Also, it may co-occur with other common mental disorders, such as anxiety disorders. However, neither comorbidity nor these other forms of depression will be a focus of this paper.

Symptom Severity

Symptom severity during the worst month was rated among those with 12-month MDD with the use of the Quick Inventory of Depressive Symptomatology Self-Report (QIDS-SR)15 A fully structured rating, the QIDS-SR has been shown to perform as well as the clinician-administered Inventory of Depressive Symptomatology and the Hamilton Rating Scale for Depression16,17. As previously proposed17, we derived severity categories of none, mild, moderate, severe, and very severe by converting QIDS-SR scores to equivalent HRSD ranges.

Functional Disability

All respondents were assessed for functional limitations in six activities of daily living( bathing, dressing, toileting, arising and transferring, continence, and eating) 18 and seven instrumental activities of daily living (climbing a flight of stairs, reaching above the head to carry something as heavy as 10 pounds, stooping, griping small objects with hands, shopping, and activities such as sweeping the floor with a broom or pruning the grass around the yard) 19. Each of the activities in the two domains was rated : 1) can do without difficulty, 2) can do with some difficulty, 3) can do only with assistance, or 4) unable to do. In this report, any respondent with a rating of 3 or 4 on any item was classified as disabled. A sub-group of 37 respondents was assessed twice, about 7 days apart, to determine test-retest reliability of the disability items. Agreement was generally very good to excellent, ranging from a kappa of 0.65 to 1.0.

A specific assessment of role impairment due to depression was also conducted. This was done with the Sheehan Disability Scale (SDS)20 for persons with 12-month MDD. The SDS was used to assess the extent to which work, household activities, relationships, and social roles were affected by depression in the worst month in the past year. A visual analogue scale was used to score responses: none (0), mild (1-3), moderate (4-6), severe (7-9) and very severe (10).

Quality of Life

All respondents also completed the World Health Organization Quality of Life assessment instrument, WHOQOL-Bref 21. The WHOQOL-Bref was developed to be a cross-culturally applicable tool for the subjective evaluation of health-related quality of life22. Designed in diverse cultural settings, including one in Sub-Saharan Africa22, it has been shown to be a valid measure of quality of life in the elderly 23. In the current sample, it has an excellent internal reliability (Cronbach alpha = 0.86).

All the instruments were translated using iterative back-translation method. As part of the translation process, all the instruments used were subjected to cultural adaptation. Thus, for example, in describing 10 Ibs in the functional assessment, a tuber of yam (a local stable) of such weight was used.

Training and Quality Control

The interviews were conducted by 24 trained interviewers, all of whom had at a least a high school education. Many had been involved in field surveys and were experienced at conducting face-to-face interviews. Interviewers received a two-week training consisting of an initial six-day training conducted by OG (which included item-by-item description of questionnaires and role play) followed by a further 2 days of debriefing and review after each of them had conducted two pilot interviews in the field. Six supervisors, all of whom were university graduates with survey experience, underwent the same level of training and monitored the day-to-day implementation of the survey.

Data analysis

In order to take account of the stratified multistage sampling procedure and the associated clustering, weights have been derived and applied to the rates presented in this report. Also, post-stratification to the target sex and age range were made to adjust for differences between the sample and the total Nigerian population (according to 2000 United Nations projections). (Table 1 presents the profile of the respondents and the results of the post-stratification adjustments). The weight so derived was normalized to reset the sum of weights back to the original sample size of 2152. We excluded 255 persons with a diagnosis of probable dementia from this total sample, thus leaving a sample of 1897 for analysis.

Table 1
Demographic distribution of the sample compared to the population on post-stratification variables

In this report, we have examined the association of MDD with socio-demographic variables of age, sex, education, and economic status. Economic status was assessed by taking an inventory of household and personal items such as chairs, clock, bucket, radio, television set, fans, stove or cooker, car, telephone, etc. The list was composed of 21 such items. This is a standard and validated method of estimating economic wealth of elderly persons in low income settings24. Respondents' economic status is categorized by relating each respondent's total possessions to the median number of possessions of the entire sample. Thus, economic status is rated low if its ratio to the median is 0.5 or less, low-average if the ratio is 0.5 – 1.0, high-average if it is 1.0 – 2.0, and high if it is over 2.0. Also, the quality of house floor was categorized into two (concrete vs. earth) as another proxy of economic status. Residence was classified as rural (less than 12,000 households), semi-urban (12,000 – 20,000 households) and urban (greater than 20,000 households)..

The analysis has taken account of the complex sample design and weighting. Thus, we used the jacknife replication method implemented with the STATA statistical package to estimate standard errors for proportions 25. Demographic correlates were explored with logistic regression analysis 26 and the estimates of standard errors of the Odds Ratio (OR's) obtained were made with the STATA. All of the confidence intervals reported are adjusted for design effects.

Role of the funding source

The Wellcome Trust was not involved in any aspect of study design, data collection, analysis, or interpretation of the data.

RESULTS

Lifetime and 12-month prevalence estimates of DSM-IV MDD were 26 .2 (95% confidence interval, 24.3 – 28.2) and 7.1 % (95% confidence interval, 5.9 – 8.3) respectively (Table 2). Women had higher lifetime and 12-month rates and so did persons who were widowed, separated, or divorced; persons of higher socio-economic status; and urban dwellers.

Table 2
Prevalence of 12-month and lifetime CIDI/DSM-IV major depressive disorder by socio-demographic characteristics

Sociodemographic Correlates

Female gender and being widowed, separated or divorced were associated with significantly higher lifetime and 12-month risks of MDD (Table 3). There was a trend for lower incomes to be associated with reduced risk of lifetime but not 12-month MDD. Compared to persons living in rural areas, the risks for both lifetime and 12-month MDD were significantly elevated among persons residing in urban areas.

Table 3
Odds ratio of 12-month and lifetime CIDI/DSM-IV major depressive disorder by socio-demographic characteristics

The distribution of economic status was significantly different according to place of residence: 34.2% of rural dwellers were in the low economic group compared with 21.2% of semi-urban dwellers and 13.7% of urban dwellers while on the other hand 15.9% of urban dwellers were in the high economic group compared to 5.1% of semi-urban residents and 2.0% of rural residents (chi square = 30.04, p< 0.001). We therefore examined the possibility that the relationship between depression and poverty might be confounded by place of residence by conducting multiple logistic regression analyses in which both variables were simultaneously entered. For lifetime prevalence, living in a house with mud floor was associated with a reduced risk for lifetime depression (OR 0.7, 95% CI 0.5 – 0.9, p = 0.012) but residence was not (OR for semi-urban 1.1, 95% CI 0.8 – 1.4; for urban 1.2, 95% CI 0.9 – 1.8). For 12-month prevalence, even though the trend for higher risks among semi-urban (OR 1.3, 95% CI 0.7 – 2.5) and urban (OR 2.0, 95% CI 0.9 – 4.2) residents persisted, neither residence nor living in mud house (OR 0.7, 95% CI 0.5 – 1.1) showed a significant association.

Onset and Course MDD

Mean age at onset was 51.0 years with close similarity between men and women (Table 4). The mean number of lifetime episodes was 2.1, also with no significant difference between the sexes. Just over one-third had received any treatment for MDD. Treatment was defined as any consultation to a health provider (orthodox, traditional, or religious) that was specifically for MDD. Men were more likely to have received treatment than women. On average, there was a 5-year delay between the onset of illness and the receipt of treatment, with the mean age at first treatment being 56.7 years. The table also shows that 38.7% of the sample had felt worthless, 36.7 had wanted to die, and 6.1% had thought of suicide. Just over 2% had attempted suicide.

Table 4
Age at onset, course and treatment for CIDI/DSM-IV lifetime major depressive disorder

Impact of 12-month IMDD on role functioning and quality of life

Table 5 shows that persons with 12-month MDD had lower overall quality of life than those without. While elderly persons with no 12-month MDD scored a mean of 13.6 on the WHOQOL-Bref, those with MDD scored 12.3, a statistically significant difference. Persons with 12-month MDD were specifically more impaired in the domains of physical and, not surprisingly, psychological functioning. However, no statistically significant difference was noticed in the environmental and social domains.

Table 5
Quality of life of persons with and without 12-month CIDI/DSM-IV major depressive disorder (n = 134)

More evidence of impairment relating to MDD is provided by the results of the analysis of the Sheehan Disability Scale (SDS). Among persons with 12-month MDD, Table 6 shows that work-related activities were mostly affected, with 83.2% reporting at least moderate impairment, 59.6% either severe or very severe and 17.5% very severe. Performance of home activities was the next most commonly affected, with 75.6% with at least moderate impairment, 11.7% being severely affected. Social role was the least affected but even here more than half of persons with 12-month MDD had at least moderate impairment.

Table 6
Severity of role impairment associated with 12-month CIDI/DSM-IV major depressive disorder (n = 134)

Correlates of Symptom Severity

The presence of clinical depression during the worst month of symptom experience was confirmed in 96.9% of those with 12-month CIDI/DSM-IV by the QIDS-SR (Table 7). Of this, 62.9% were classified as having at least clinically moderate depression, 28.9% severe or very severe depression. Quality of life impairment was linearly related to severity, with mildly depressed elderly persons having the least impaired quality of life and very severely depressed persons having the worst. The rates of any functional disability as well as the intensity of role impairment, as measured on the SDS, were also linearly related to severity of 12-month depression.

Table 7
Pattern and correlates of symptom severity 12-month CIDI/DSM-IV major depressive disorder

Lifetime Treatment

Table 8 presents the results of the examination of predictors of lifetime treatment for MDD. Treatment included any consultation to a health provider, either orthodox or complimentary, Females were significantly less likely to have ever received treatment and so were those who were widowed, separated or divorced. There was a progressively reduced likelihood of ever receiving treatment as economic status fell: compared with persons in the highest economic group, those in the lower groups were less likely to have received treatment and this was a meaningful (statistically significant) decrease for those in the low and low average categories. Residence was related to receipt of treatment: compared with persons residing in rural areas, those in urban areas were three times as likely to have received treatment.

Table 8
Bivariate socio-demographic predictors of lifetime treatment among respondents with lifetime CIDI/DSM-IV major depressive disorder (n = 498)

COMMENT

To our knowledge, this is the first large community-based study of MDD in elderly persons in Sub-Saharan Africa in which replicable ascertainment procedures have been used. Our results suggest that, in the period 2003/2004, about 7% of elderly persons in the Yoruba-speaking areas of Nigeria had experienced DSM-IV MDD in the prior 12-months and 26.2% had done so in their lifetimes. MDD was associated with considerable impairment. Compared with persons without MDD, those with 12-month diagnosis had a worse overall quality of life. Most were at least moderately impaired in work-related activities (83.2%) or in home duties (75.6%). One limitation of our report is that it deals only with MDD as defined in the DSM-IV12. Other forms of depression exist and may have different profiles and correlates in our sample. Caution is also required in interpreting the results as incidental findings might have resulted from multiple significance testing.

Rates of depression raging from a low of 0.7% to a high of 15.5% have been reported among the elderly 27 and there have been controversies about the best way to measure depression in the elderly28,. In a review of community prevalence studies, most conducted in Western Europe and North America, a weighted average prevalence of 1.8% was reported29. However, most of the studies had used substantially different ascertainment procedures than we used in our survey. A study in the US in which the Diagnostic Interview Schedule, a forerunner of the CIDI, was used to ascertain DSM-IV MDD found a current (point) prevalence of 3.8% and a lifetime prevalence of 15.8% 30. Our rates are therefore considerably higher than commonly reported. In the current study, persons who received a diagnosis of MDD did indeed have a clinically significant disorder: 96.9% of those with 12-month diagnosis were confirmed by an independent assessment of clinical rating of symptom severity with 62.9% of them rated as having at least moderate depression and 28.9% as severely or very severely depressed.

The mean age of onset of MDD was about 51 years in this sample. This is much later than reported in studies conducted in Western Europe and North America where, typically, the mean age of onset of MDD is about 30 years31. In a previous report, using data derived from the Nigerian Survey of Mental Health and Well-being, a general population survey, we found a median age of onset for depression of about 45 years 14. The delayed age of onset provides a plausible explanation for the low prevalence of 1.0% found in the general adult population in that study14 but only a partial explanation for the considerably higher prevalence among elderly persons reported here, even though both studies were conducted in the same setting and with identical ascertainment tools. It is important to note that in the general population study, even though persons aged 65 years and over constituted only about 6.1% of the weighted sample, there was a clear trend for higher rates of MDD among them. Thus, while the overall prevalence estimates of lifetime and 12-month MDD were 3.0% and 1.0% respectively, the respective estimates among persons aged 65 years and over were 5.3% and 1.5%. We believe that several factors may account for the high rates of MDD among the elderly. One possibility is that elderly people may be more likely to endorse symptoms of depression in a survey interview. This may reflect a less stigmatizing attitude to mental illness by elderly persons32. Another possibility is that the harsh social and economic situation in Nigeria may be particularly pathogenic for elderly people with few personal resources to cope. With failing physical health, much of which may go without adequate medical care, increase in the experience of loss to which older persons are susceptible, and dwindling traditional support and social status, old age may constitute a particularly risky period for depression.

In spite of the late onset of MDD, the observations of a mean number of episodes of about 2.1 and a ratio of 12-month prevalence to lifetime prevalence of about 30%, suggest that MDD in this sample shows the same pattern of chronicity and recurrence that have often been reported 33. The symptom pattern also shows that features indicative of clinically significant depressive disorder were present in this sample and could be identified in the culture. Indeed, symptoms such as ideas of worthlessness and of guilt, as well as suicidal thoughts, all indicative of moderate to severe depression, were relatively common. Thus, even though the predictive validity of DSM-IV defined MDD remains to be determined in an African setting, our findings do indicate that, cross-sectionally, those who receive the diagnosis do have a “disorder”.

Sociodemographic correlates of both lifetime and 12-month disorders were generally few.We found higher rates of MDD among persons of higher economic status. The effect was stronger for current than lifetime prevalence suggesting a trend for a worse course among such persons as well. Previous studies have often suggested that poverty might elevate the risk for major depressive disorder34. Several reasons might account for our finding. Persons of lower economic status might have a tendency to deny symptoms of MDD, in which case our finding is an artifact. On the other hand, it could be that social protective factors are stronger among poor elderly persons, possibly by retention of traditional social networks and availing themselves of the buffer that religious affiliations might offer. The significant association of MDD with urbanicity disappeared once economic status was controlled for in view of the overlap between the two variables. Nevertheless, the trend of the was revealing: compared with rural dwellers, increased risk was found among semi-urban residents while urban dwellers had the highest risk. This “dose response relationship” suggests that there is indeed some features of urban living that increase the risk of elderly Nigerians becoming depressed. The rate of urbanization in Nigeria, among the highest in the world 6, is clearly a major issue for the health and wellbeing of the elderly in the country. We speculate that the attenuation of the extended family support in the city might be stripping away the protective buffers that elderly persons enjoy in traditional African settings.

Elderly persons with MDD had poorer overall quality of life and specifically lower quality of life in the physical and psychological domains, confirming the association between poor physical functioning and depression in the elderly35. The observations that 62.9% of those with 12-month CIDI/DSM-IV MDD were independently rated to have at least a moderate disorder and that increasing severity of disorder was associated with worse quality of life, higher rates of functional disability, and higher levels of role impairment are all indicative of the considerable burden that depression connotes. These findings also further support the clinical validity of MDD in this population and argue against any notion that rates might be attributable to “category fallacy”36.

Our findings highlight a high level of unmet need for treatment of depression in this sample. In this survey, only about 37% of elderly persons with lifetime depression had ever received any form of treatment, either from orthodox or traditional health providers, for their MDD, with men more likely to have ever done so. Given the predominant urban distribution of health facilities and out-of-pocket payment for health service in Nigeria, the associations of low economic status and of rural dwelling with reduced likelihood of treatment for MDD is not surprising. Previous studies conducted in more developed Western countries suggest that, even though under treatment is a common problem, when treatment is given, elderly depressed patients commonly respond 37. The level of impairments that elderly persons with MDD have speaks directly to the need for a scaling up of effective treatment for those affected 38.

ACKNOWLEDGEMENT

Funding for the Ibadan Study of Ageing was provided by the Welcome Trust.

Footnotes

CONFLICT OF INTEREST STATEMENT

Oye Gureje: None. Has full access to all the data in this study and has full responsibility for the decision to submit for publication.

Lola Kola: None.

Ebenezer Kolawole Afolabi: None

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