Prevalence of hypertension and prehypertension among children and adolescents in a semi-urban area of Uyo Metropolis, Nigeria

Introduction In the past, Hypertension in childhood was not considered a problem but in the last few decades, it has gradually become a source of concern especially as children are known to maintain their blood pressures into adulthood. Therefore, hypertensive children are at risk of developing cardiovascular complications earlier in adulthood. In our own environment, the prevalence of hypertension in children is undocumented, hence the purpose of this study. Methods Two hundred children aged between 3-17 years were recruited into this study from two public schools-one primary, one secondary in a semi urban community in Uyo metropolis. The blood pressure of respondents was measured in accordance with the technique described by the 4th Task Force on Blood Pressure Control in Children. The height and weight of all eligible subjects was measured using a stadiometer and a calibrated scale respectively. Body Mass Index (BMI) was assessed for each subject and World Health Organization (WHO) charts of BMI for age and sex were used as reference standards. Waist circumference was measured according to the technique described in the National Health and Nutrition Examination Survey. Results The prevalence of hypertension and prehypertension was found to be 3.5% and 2.5% respectively in this study. Only age (OR = 1.74, p = 0.005, 95%CI = 1.186-2.566), BMI (OR = 1.54, p = <0.001, 95% CI = 1.249-1.913) and waist circumference (OR = 1.16, p = 0.002, 95%CI = 1.056-1.271) were found to significantly predict the development of high blood pressure. Conclusion The prevalence of hypertension and prehypertension in this study was found to be low. Hypertension/prehypertension was more likely to develop with increasing age, BMI and waist circumference.


Introduction
Hypertension is fast becoming a source of growing concern in children in developing countries [1]. Children with elevated blood pressures (BP) tend to maintain those same levels of blood pressure into adulthood, therefore, early detection is essential to minimize complications later in life [2]. In children, hypertension is said to be present when the systolic and diastolic blood pressure is greater than the 95 th percentile for the child's age, sex and height on three or more occasions [3]. The Fourth Report of the Task Force on Blood Pressure Control in Children commissioned by the National Heart, Lung and Blood Institute (NHLBI) has also introduced a new category of elevated blood pressure called prehypertension. This condition is diagnosed when a child´s average BP exceeds the 90 th percentile but is less than the 95 th percentile for age, sex and height. Any adolescent whose BP is greater than 120/80 mm Hg is also given this diagnosis, even if their reading is less than the with none in Uyo, Akwa Ibom state [7,8]. Since hypertension is a major risk factor for cardiovascular disease and there is evidence that childhood hypertension can predispose to hypertension in adulthood [9], this study is timely as it will help to add to the body of evidence on childhood hypertension and help bring about interventions to limit this non-communicable disease in our environment. This study was therefore undertaken to assess the prevalence of hypertension and prehypertension among children in Uyo and to determine the relationship, if any, between childhood hypertension and certain factors such as age, gender, socioeconomic status and family history of hypertension.

Methods
This cross-sectional study was conducted in Etoi which is located to the north of Uyo metropolis, Akwa Ibom State, Nigeria. Etoi is one of the four clans that make up Uyo local government area and consists of twenty-two villages. Mbiabong is one of the villages in Etoi and consists of four communities. The population is predominantly Ibibio/Annang speaking. However, other ethnic groups such as Igbos, Yorubas and Hausas also reside there. A simple random sampling method was used to select Mbiabong community. Mbiabong has three primary schools and one secondary school. Consequently, one primary school was selected by random sampling from the three primary schools while the only secondary school was selected. Two hundred children aged between three and seventeen years irrespective of their ethnic group were recruited into the study, one hundred from each school. In each school, a total of seventeen students were selected randomly by a simple random sampling (balloting) technique from each class arm i.e. classes 1-6 for the primary school and junior (JS 1-3) and senior secondary school classes (SS1-SS3) for the secondary school.
Sample size was calculated using the formula for calculating sample size for a cross sectional study [10] where z is the standard score Details of the study objectives, procedures and potential benefits were explained to the study respondents during the initial visits and consent was sought and obtained from both respondents and their parents. Personal data such as age, gender and health condition (both previous and current) of the respondents was obtained using a structured questionnaire. Subjects were also classified into five social classes based on the Oyedeji socioeconomic classification scale [11]. This scale takes into cognizance both parents'/guardian's occupation and educational levels on a score of 1-5. The mean of the total of the four scores i.e. father's occupation + father's educational level + mother's occupation + mother's educational level divided by 4 to the nearest whole number gives the social class. Social class 1 is the highest class while social class 5 is the lowest but for the purposes of this study, social classes 1, 2 and 3 are classified as high socioeconomic class while classes 4 and 5 are classified as low socioeconomic class. This is as outlined below: Table 1. Family history of hypertension was also sought and obtained with a subject being classified as having a positive family history of hypertension only if the disease is present in a first-degree relative. The height and weight of all eligible subjects was measured using a stadiometer and a calibrated scale respectively recorded to one decimal place. Body Mass Index (BMI) was assessed for each subject and World Health Organization (WHO) charts of BMI for age and sex were used as reference standards.
Respondents with BMI above the 95 th percentile were considered obese while those with BMI between the 85 th and 95 th percentile were considered overweight. Waist circumference was measured according to the technique described in the National Health and Nutrition Examination Survey (Anthropometry procedures manual) [12]. The Blood pressure was measured using the mercury gravity sphygmomanometer with an appropriate sized cuff for age being used. The subject was placed in a sitting position with the right upper arm placed on a table after the subject had been allowed to rest for at least 15 minutes before the procedure. The technique of BP measurement adopted was as described by the 4 th Task Force on Blood Pressure Control in Children [3].
The first Korotkoff sound was taken as the systolic pressure while the fifth Korotkoff sound was taken as the diastolic pressure. The blood pressure measurement was carried out by the three coinvestigators separately on each subject with the average of the three readings taken as the blood pressure of the subject.
Hypertension was diagnosed if blood pressure either systolic, diastolic or both was more than the 95 th percentile for age, sex and height while pre-hypertension was diagnosed if blood pressure ranged between the 90 th and 95 th percentiles. Those with a diagnosis of pre-hypertension and hypertension had two subsequent consecutive blood pressure measurements at two weekly intervals.
Data was analysed using the STATA statistical software version 10.  Table 2 shows the sociodemographic and clinical characteristics of the study subjects. More than half (56%) of the respondents are between 13-17 years. The majority (64%) are females. Almost half (44%) belonged to social class 3. A greater proportion (81.5%) had a negative family history of hypertension with a normal BMI (95%). Table 3 shows the frequency of occurrence of hypertension and prehypertension with the prevalence of pre-hypertension and hypertension being 2.5% and 3.5% respectively.

Conclusion
In conclusion, the prevalence of hypertension and prehypertension in our study populace appears to be low. Amongst the factors investigated in this study, only age, BMI and waist circumference were significantly associated with the development of hypertension and prehypertension. The low prevalence of hypertension and prehypertension in this study notwithstanding, with the increasing rate of urbanization prevalent in many Nigerian cities and the attendant changes in lifestyle, early health education is a prerequisite as an intervention to help in forestalling the morbidity/mortality from cardiovascular disease that has been observed in other environments.
What is known about this topic  Prevalence of hypertension in childhood varies from place to place;  Hypertension in childhood can act as a precursor to hypertension in adulthood.

What this study adds
 Prevalence of hypertension in the study populace is still low;  Age, BMI and waist circumference were significantly associated with the development of hypertension and prehypertension in childhood.

Competing interests
The authors declare no competing interests.

Authors' contributions
Frances Okpokowuruk participated in blood pressure measurements and collection of other data via the questionnaire. She also wrote the introduction and discussion. Mkpouto Akpan wrote the methodology and also participated in collection of data while Enobong Ikpeme also was involved in data collection and critiqued the entire manuscript.

Acknowledgments
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