Awareness of hypertension and its impact on blood pressure control among elderly nigerians: report from the Ibadan study of aging

Introduction Hypertension is highly prevalent among the elderly. Its awareness has a direct influence on control through drug adherence. Earlier studies have shown that awareness of hypertension is low among sub-Saharan African populations but only a few studies have looked at the prevalence and awareness of hypertension among the elderly. Methods The Ibadan Study of Ageing is a longitudinal cohort study of the mental and physical health status as well as the functioning of elderly persons residing in the Yoruba-speaking areas of Nigeria. Study was conducted in multiple waves from 2003/2004 to 2009. This report is based on the sample studied in 2007 (N = 1469). Respondents, aged ≥ 65 years, were assessed for the presence of hypertension, its awareness, receipt of and adherence to medication for the condition, and effectiveness of treatment on the control of blood pressure. Blood pressure was measured with the use of digital monitors (Omron MS - 2 Basic Model). Awareness of the diagnosis of hypertension was ascertained by self-reports. We explored social, economic, demographic and clinical correlates of the presence of hypertension, its awareness and control using multiple logistic regression analyses. Results The sample was composed of 809 (55.1%) females and 666 (44.9%) males. The mean age of the participants was 76.9 ± 8.4 years. Hypertension (defined as previous diagnosis by a health provider or a measured blood pressure higher than or equal to 140/90 mm Hg) was recorded in 973 (62.2%) participants, with females having a prevalence of 61.4% and males that of 70.1%. Other than female gender, residing in urban/semi urban areas and being overweight or obesity were associated with the occurrence of hypertension. Among those assessed to have hypertension, 78% were not previously aware of its presence. Factors independently associated with lack of awareness of hypertension included low socioeconomic class (OR 8.21, 95% CI 3.72-18.11, P < 0.001), and BMI >25kg/m2 (OR 3.11, 95% CI 1.36-7.09, P < 0.009). Among those who were aware of the presence of hypertension and were on treatment, 77.3% still had uncontrolled hypertension. Only obesity or overweight (OR 5.56, 95% CI 1.35 - 22.83, P < 0.016) was independently associated with poor blood pressure control. Conclusion The prevalence of hypertension among elderly Nigerians is high and those affected are often not aware of having the condition. Only a minority of those who receive treatment for the condition have adequate blood pressure control. The findings highlight the need for improved healthcare for the growing population of elderly persons, with particular attention to early detection and effective control of the condition.


Introduction
Systemic hypertension is a disease of public health importance. As the single most important risk factor for cardiovascular death and disability, it accounted for 7.5 million and 9.4 million deaths worldwide in 2004 and 2010 respectively [1]. In the year 2000, about 26.4% of the world adult population were living with hypertension and it is projected that this figure will increase to about 29.2% by 2025 [2]. Low and middle-income countries (LMIC) bear the majority of the burden associated with hypertension.
Estimated total number of adults with hypertension in high income countries in 2000 was 333 Million while it was 654 Million in LMIC [3]. With an expected 60% increase by 2025, it is estimated that the total number of affected persons will rise to 1.56 Billion adults globally [3,4]. Among the sequelae of uncontrolled hypertension are stroke, multi infarct dementia, heart failure, myocardial infarction and renal failure [5]. The burden of hypertension is more among the elderly population in view of its higher prevalence and associated morbidity and mortality in this age group [6]. Agedependent positive association exists between systolic blood pressure and diastolic blood pressure (SBP/DBP) on the one hand and stroke and ischaemic heart disease on the other hand [7].
Increasing age is associated with a progressive rise in risk of vascular mortality with a 20 mmHg rise in SBP above 125 mmHg or 10 mmHg above DBP of 75 mmHg, and this observed risk is common among the elderly population [6,8].
Despite the high burden of hypertension, most affected persons are not aware of its presence, thus increasing the occurrence of associated complications, particularly among elderly populations [9,10] Nigeria only about 30% of persons with the condition was aware of it at the time of diagnosis [1,11]. Optimal control of hypertension has been shown to reduce the risk of cardiovascular complications, particularly that of SBP which is more prevalent among the elderly population [5,12]. The knowledge and awareness of the diagnosis as well as of the risk associated with uncontrolled hypertension tend to enhance patients' adherence to lifestyle modifications and to medications [13,14]. With a growing elderly population in sub-Saharan Africa, adequate knowledge about the awareness, control and treatment of hypertension will be required to guide the development of policies designed to reduce the burden of hypertension in the population. We carried out a secondary analysis of data from the Ibadan Study of Ageing with the aim of determining the prevalence, awareness, treatment and control of hypertension among the study population.

Sampling
The Ibadan Study of Ageing is a longitudinal community based cohort study of the mental and physical health status as well as the functioning of elderly persons (aged ≥ 60 years) residing in the Yoruba-speaking areas of Nigeria, which consists of eight contiguous states in the Southwestern and North central regions (Lagos, Ogun, Osun, Oyo, Ondo, Ekiti, Kogi and Kwara). The population of these states at the time of study was approximately 25 million people, which was about 22% of the Nigerian population.
The baseline characteristics and methodology have been fully described in earlier reports [15,16], thus only a brief summary is reported here. Respondents were selected using a multistage stratified area probability sampling of households. In households with more than one eligible person available (aged ≥ 60 years and fluent in Yoruba, the language of the study), the Kish table was used to select one respondent. All the eligible respondents were approached after ethical approval was sought and obtained from the institutional review board. A total of 2,152 respondents were recruited for the study with a response of 79% while 3 respondent records were excluded for incomplete data. This baseline assessment was carried out between August 2003 and November 2004. The non-response rate was due to change in address or not found at home after repeated visits rather than refusal. The cohort was followed up in 2007 in the first of 3-wave annual assessments.

Data collection
Assessment was carried out on the participants through face-to face interviews. The interviews were conducted by 24 trained interviewers all of whom had at least a high school education. Many of the interviewers had previously been involved in field surveys and had experience of face-to-face interviews. Interviewers undertook two weeks of training, consisting of an initial 6-day training delivered by one of the authors (OG) (which included item-by-item description of questionnaires, measurement of blood pressure, role plays, as well as other assessments), followed by a further two days of debriefing and review after every interviewer had done two practice assessments in the field. Six supervisors, all of whom were university graduates and had survey experience, underwent the same level of training and monitored the day-to-day implementation of the survey.

Measures
Along with several other assessments, a checklist of chronic physical and pain conditions was included in the Ibadan Study of Ageing [16]. At the 2007 follow-up, respondents were asked if they had been told by a physician that they had diabetes mellitus or hypertension. Questions were asked about the use of antihypertensive medications and adherence, the presence or past history of complications of hypertension. Also included were selfreported histories of other chronic illnesses. Blood pressure was measured using a validated digital monitor (Omron MS -2 Basic Model). The measurements were taken in sitting position after at least 5 minutes rest. Three measurements were recorded approximately 5 minutes apart and the average determined.
Hypertension was defined using World Health Organization (WHO) definition which defined hypertension as previous diagnosis of hypertension by a physician, use of antihypertensive medications or systolic blood pressure (SBP) of 140 mmHg and above or diastolic blood pressure (DBP) of 90 mmHg or greater (18). Hypertension was adjudged to be controlled if SBP was less than 140 mmHg and DBP was less than 90mmHg in those who reported having been previously told that they had hypertension and were on medication [17]. Diabetes mellitus was based on self-reported previous diagnosis of the condition or use of antidiabetic agents. Transient Ischaemic Attack (TIA) was defined as occurrence of sudden onset of focal or global neurological deficit that resolved within 24 hours of onset [18]. Depression was assessed using the World Health Organization (WHO) Composite International Diagnostic Interview, version 3 (CIDI.3), a fully structured diagnostic interview [19]. As previously described, diagnosis of dementia was made using validated protocols previously used in our setting [20].

Data analysis
Data was analyzed with the STATA statistical package, version 14.
Weights were derived and applied to adjust for the clustering associated with the stratified multistage sampling method. Post Multivariate analyses were then employed to identify factors that were independently associated with hypertension, its awareness and blood pressure control. We classified the economic status of participants using an inventory of 21 household and personal items such as chairs, radio, television sets, cookers, and iron (wealth index). Each respondent's status was determined relative to the median number of possessions in the total sample. Thus, economic status was then classified as low (≤ 0.5 of the median); lowaverage (> 0.5-1.0); high-average (> 1.0-2.0) or high (> 2).

Results
The records of one thousand four hundred and sixty nine elderly persons with complete data were analyzed for the study. Of these,  Table 2). Seven hundred and fifty nine participants (78%) with high blood pressure were not aware of having hypertension. On univariate analysis, individuals who were not aware of their hypertension were more likely to be older than 69 years, currently unmarried, of low socioeconomic class, overweight or obese (BMI > 25kg/m 2 ) and were less likely to report having diabetes mellitus and dementia (Table 3).

Discussion
The result of this study showed that hypertension is highly prevalent among elderly Nigerians and that the majority of affected individuals are females. Approximately 78% of persons with hypertension were not aware of the condition while among the few who were aware, the hypertension was uncontrolled in 77.1% despite reporting that they were on treatment. Factors independently associated with lack of awareness of hypertension included age less than 69 years, individuals with no self-reported history of diabetes mellitus and BMI ≥ 25kg/m 2 . Majority of the patients who were previously aware of their hypertension had poor blood pressure control. Having depression in the last 12 months and a BMI ≥ 25kg/m 2 were independently associated with poor blood pressure control. The prevalence of hypertension in this population is much higher than in the general population, however the finding is similar to those of other studies among elderly populations [3]. The high prevalence of hypertension among elderly women when compared to men can be explained by the loss of the estrogen cardiovascular protecting effects after menopause. The high prevalence of hypertension has policy implications towards planning appropriate intervention for the growing health needs of the rising elderly population in the country.
Hypertension was high among the urban and semi urban dwellers in this population and this is in agreement with reports from other previous studies [11][12][13]. The reasons for the high prevalence of hypertension in the urban settings could be attributed to constant exposure to stress, lack of or inadequate exercise and consumption of unhealthy diets, such as fast foods, which are high in salt and fat. Individuals in the low socioeconomic class were less likely to be aware of their hypertension in this study and the relationship between hypertension awareness and socioeconomic status has been well documented by several studies [14,28,29]. The Page number not for citation purposes 5 prevalence of hypertension and its awareness was higher in urban sub -population of the study compared to the rural population. This finding is similar to report from other studies [24,29]. Among subjects with hypertension who were on treatment, only 22.7% were controlled. This is at variance with reports from high income countries [9-13, 27, 29]. The finding in our study is similar to the report by Akinkugbe et al who observed that only a third of persons with hypertension and on medications had optimal blood pressure control [30]. The low rate of hypertension control may be due to

Competing interests
The authors declare no competing interest.

Authors' contributions
YRR, was involved in the data analysis and interpretation, manuscript writing and editing. TA was involved in data analysis, interpretation and manuscript editing. While OG was involved in the study conceptualization, designing, data collection, data analysis and interpretation and manuscript editing. All authors have read and agreed to the final version of this manuscript.

Acknowledgments
The Wellcome Trust provided funding for the Ibadan Study of Aging. The Wellcome Trust had no part in the design, methods, subject recruitment, data collection or analysis, or preparation of the manuscript.
Page number not for citation purposes 6 Tables   Table 1: Demographic and clinical characteristics of all subjects