The association between physical activity and hypertension among HIV positive and negative populations in rural South Africa


 Background Hypertension is a public health problem in sub-Saharan Africa, with considerable under- diagnosis, poor management, and lack of community-wide preventive strategies. Hypertension is a common condition in South Africa and is a risk factor for heart attacks, stroke, left ventricular hypertrophy, renal disease, and blindness. In this research study, we identify and examine the trend of physical activity within South Africa's HIV-positive and negative rural communities. Methods This was a secondary analysis of cross sectional survey data from the Agincourt Health and Socio-Demography Surveillance System Site (AHDSS) that were collected over a period of 10 months, from August 2010 to May 2011. All 4436 individuals participating in the AHDSS survey were included. The inclusion criteria for the survey were from aged 15 years or older, and a permanent resident according to the 2009 census. The participants were interview (approximately 45 minutes) on chronic disease risk factor [applying] a questionnaire; anthropometric measurement were taken, blood pressure (BP); point-of care analysis of lipids and glucose; and dried blood spot collections for HIV and ELISA testing were conducted. ResultsThe research findings showed a significant/strong association between hypertension and HIV in both univariate and multivariate analysis. In many developed countries, the prevalence of hypertension among HIV-positive individuals varies between 8% and 39%. A study in Kenya reported a lower prevalence of 7.4%–11.2%, compared with 22.1%– 32.2% in study. ConclusionHypertension is common in HIV-infected adults and is likely because of a combination of known risk factors, levels of physical activities/sedentary way of life, HIV-specific factors, and ART. There is a need for broad, global cohort studies to improve our knowledge and understanding of the above named subject matter, interventional studies are needed to discover new approaches in hypertension and HIV-infected individuals in South Africa and sub-Saharan Africa to avoid and manage hypertension and hypertension-related cardiovascular diseases among HIV infected persons especially in this era of epidemiologic and demographic transition in LMICs.

hypertension and hypertension-related cardiovascular diseases among HIV infected persons especially in this era of epidemiologic and demographic transition in LMICs.

Background
Hypertension, also known as high or raised blood pressure, is a condition in which the blood vessels have persistently raised pressure. Hypertension is a public health problem in sub-Saharan Africa, with considerable under diagnosis, poor management, and lack of community-wide preventive strategies [1]. Hypertension is a common condition in South Africa and is a risk factor for heart attacks, stroke, left ventricular hypertrophy, renal disease, and blindness [2]. People who have hypertension are usually unaware that they have the condition, unless their blood pressure (BP) has been measured at a health-care facility. It is therefore frequently referred to as a silent epidemic. Consequently, hypertension is universally inadequately treated, resulting in extensive target-organ damage and premature death(1). Hypertension frequently co-exists with other risk factors for chronic diseases of lifestyle (CDL), such as diabetes, obesity and physical inactivity. These interrelationships of hypertension with other CDL risk factors and the various possible targets organs that can be influenced by uncontrolled hypertension result in a diverse picture that has an impact on the South Africa population [2]. Physical inactivity in particular, has been related to increased risk of hypertension.
Over the past few decades, the physical activity patterns in the developing regions of the world have been changing from labour-intensive lifestyles to more sedentary and less physically demanding activities facilitating the development of CDL such as hypertension [3]. Physical activity has been shown to be an effective intervention to decrease BP the more one exercises, the greater the reduction in the risk of hypertension. This is because increase effective cardiovascular circulation of Therefore, studying the association between physical activity and hypertension is important, since these can help to inform policies and educate people and improve health service delivery and further research into drug and diagnostic development.

Study Design
This was a secondary analysis of cross-sectional survey data from the Agincourt Health and Socio-Demography Surveillance System Site that were collected over a period of 10 months, from August 2010 to May 2011.

Study setting
The Agincourt Health and Socio-Demography Surveillance Site (AHDSS) monitors 90,000 people in 15,500 households living in 27 villages and is operated by the Medical Research Council (MRC)/Wits

Rural Public Health and Health Transitions Research Unit. The site is situated in Northeast South
Africa in the Bushbuckridge sub district of Ehlanzeni in Mpumalanga province. The site has annually recorded information on death, births, migration, marital status, education attainment, employment and socio-economic in this population since 1992 [24].

Study Population
All individuals participating in the AHDSS survey that was conducted from August 2010 to May 2011.

Method used in primary study
The survey included 7662 individuals from a population of 34,413 using the 2009 HDSS census round sampling frame.
All sampled persons were visited by interviewers trained in the field research protocol, HIV counseling, and collection of dried blood spots (DBS) up to three times in their homes. The home interview (approximately 45 minutes) included a chronic disease risk factor questionnaire; anthropometric measurements including height, weight, hip circumference and blood pressure (BP); point-of care analysis of lipids and glucose and dried blood spot collections for HIV [25].

Physical activity assessment
Physical activity was assessed by questionnaire asking, in detail, frequency and duration of physical activity for work, transportation and leisure during a typical week (see appendix 1). Weekly physical activities were subsequently categorized into six groups: vigorous activities, moderate activities, travel to and from places, recreational activities, sedentary behavior and work.

Blood pressure measurement
Blood Pressure was measured three times on the right arm of the seated respondent using an automated recording instrument OMRON R6 Wrist Blood Pressure Monitor. The averages of the second and third systolic Blood Pressure (sBP) and diastolic Blood Pressure (dBP) measurements readings were used to estimate dBP and sBP Height was measured in centimeters (cm), weight was measured in kilograms (kg), waist circumference was measured in centimeters (cm) and the hip circumference was measured in centimeters (cm) [26]. And used to calculate body mass index (weight divided by squared height) and waist-to-hip ratio.
Blood pressure was classified following standards recommend by WHO, Normal Blood pressure was defined respectively for Systolic BP 120 mmHg and Diastolic BP 80 mmHg. For Pre Hypertension was also defined for Systolic BP >120 mmHg and < 139 mmHg and Diastolic BP >80 mmHg and <89 mmHg. For Hypertension Systolic BP >140 mmHg and Diastolic BP >90 mmHg or use of antihypertensive medication [27].

Ascertainment of HIV Status
Informed consent was obtained prior to study enrolment. A confidential interview was conducted where participants were asked about contraceptive history for females and circumcision history for males. For HIV testing, blood spots were tested by using screening assay Vironostika Uniform 11 (Biomerieux, France), and positive results were confirmed by the SD Bio line HIV ELISA test as it is the standard diagnostics test for HIV. A third assay was done in cases where the screening and confirmatory tests did not match, and this was used to determine the final result of the test following WHO criteria [25].

Assessment of Potential Confounders
Anthropometric measurement assessed BMI, categories of WHR, were measured at all visits while the participant wore light clothing and no shoes. Elevated blood glucose, elevated lipids were also measured at each visit. Gender, age, union status, education, smoking status, alcohol intake and History of chronic diseases were assessed by using questionnaire during interview the participants that were asked about smoking status and alcohol intake.

Exposure variables:
Vigorous work activity, vigorous activities, moderate activities, travel to and from places and sedentary behavior.

Outcome variables:
Hypertension and HIV status Potential confounders' variables: Gender, age , union status, education, BMI, elevated blood glucose, categories of WHR, elevated lipids, smoking status, alcohol intake and History of chronic diseases

Data cleaning
Data cleaning and all data analysis were done using STATA 13. Standard data cleaning procedures to identify values on variables were carried out by conducting checks on all extracted variables to determine the extent of missing values and duplicated variables. (A 20% cut off point was used to delete observations with missing values and above 20% was retained).

Generating new variables in the data and coding
We generated three categories of smoking status and alcohol consumption: as never, past and current. History of chronic diseases were generated with two categories; Yes and No, every participant who had diabetes and who was diagnosed with stroke were included under the category yes. We generate a new variables called blood pressure that included systolic BP and diastolic BP, and were coded with three categories: low, normal and high. We generate a new variable called Hypertension with two categories: yes and no. categories of BMI (body mass index) Weight/height2 were coded into four categories: underweight, normal weight, overweight and obese, the participants with the BMI; less than 18.5 were considered as underweight, 18.5 -24.9 were considered as normal weight, 25 -29.9 were consider as overweight and the BMI of 30+ were considered as Obese.
Education was categorized into four categories: none, primary, secondary and tertiary. Union status was categorized into three categories: single, in a relationship, and unknown.

Analysis
Description of the levels of physical activity among HIV positive and HIV negative individuals: Descriptive frequency tabulation was conducted to know and understand the distribution of physical activity according to HIV status. Prevalence of hypertension was described using proportion and percentages. A chi square test was used to check an association between the two categorical variables. For continuous variables, summary statistics were used; two sample t-tests were used to compare the means of two continuous variables (e.g BMI and hypertension) after the normality assumption was conducted using graphical and shapiro-wilk test.
Bivariate and multivariable logistic regression analysis were used to test the study hypotheses and the factors influencing the associations of PA and Hypertension to HIV negative and HIV positive. In the multivariate analysis we adjusted for the covariates gender, age, union status, education, BMI, Smoking status, alcohol consumption, HIV status, and history of chronic diseases, categories of WHR, elevated lipids, blood glucose and physical activities. All these covariates were included based on a pvalue of < 0.20 in the bivariate analysis.

Ethical Statement
The primary study was approved by the University of the Witwatersrand Human Research Ethics   40.02% had no hypertension. The relationship between these two variables was found to be significant (with a p value of 0.0001).  In summary, the association between the outcome variable ( Hypertension) and the explanatory variables namely ,gender, age group, marital status (HIV negative), education (HIV negative), BMI, alcohol, smoking status and history of chronic disease (HIV negative) all had a statistically significant p-value of less than 0.05 at 95% confidence interval. It showed that there was a relationship/association existing between these individual variables and hypertension. However     1.05; 1.11] for a unit increase in blood glucose level. After adjustment, blood glucose showed a relatively protective factor with a 2% less chances of hypertension; however it was not statistically significant.

Table 3. Description of physical activity pattern among HIV positive and HIV negative
P trend was adopted from metabolic physical activity, p-value as a combined value to understand statistical significances relationship if any, for all the physical activity types with hypertension. A statistically significance relationship was attained in univariate analysis with a p-value of 0.001 meaning, there was an association between physical activity types and hypertension. After adjusting for possible confounders, a non-statistical significance p-value of 0.137 was achieved, indicating there was no association found between physical activity and hypertension.

Discussion
This study employed a cross sectional survey data from the Agincourt Health and Socio-Demography Surveillance System, it looked at the association between physical activity and hypertension among HIV positive subjects compared to HIV individuals in rural South Africa setting.

Physical Activity association with Hypertension
The results in the study showed that physical activity is associated with hypertension in rural South Africa communities and this is in consonance with similar different studies that were conducted in other parts of the world including other Africa nations [2].
There are some experimental evidence from interventional studies that further support this assertion/relationship between physical activity and hypertension.
It is an established fact that effects of exercise on blood pressure helps in preventing hypertension. It is also a well-documented and characterized element by various studies in recent years [2,4]. Some other studies have shown that physical inactivity is a risk factor for hypertension, this is also an accepted view by many other researchers who worked across the globe, numerous consensus statements and recommendations have also been published [3,4,5].
Most of the studies on hypertension risk and physical activity relied on questionnaire data to stratify participants by activity patterns, example, as sedentary, active or inactive. This categorization allows for comparison between the extremes of activity levels, results of such surveys showed higher rates of elevated BP in sedentary versus active individuals [7,8,9,10,11,12]. A few surveys however, showed that there is no difference in hypertension risk factors and levels of activity [13,14,15].

Hypertension in rural South Africa /sub-Saharan
Hypertension have been shown to be associated with physical inactivity [6]. In population-based surveys, high rates of hypertension were found among older adults in rural and urban South Africa communities, 44.0%-52.0% among men and 51.6-60.4% among women in 1998 [7].
These assertion agrees with our research study/outcome. Older adults are more affected by hypertension, which is an established risk factor for cardiovascular disease [8].
Our results in the present study further support the above statement and other previous study findings on hypertension in rural South Africa and sub-Saharan Africa.
Our research study also revealed that women [56.8%] had higher rate of hypertension in contrast to men [43.2%] the reason [in the present study] could be that men are more physically active than women, the study also revealed that the risk of hypertension was more in older adults compared to younger ones, especially those between the age group 40 -70 years above. The reason for such an anomaly could be that young adults are more physically active than older adults, and as a result offers a protective factor to younger adults to have nether risk of contracting hypertension in comparison to older adult subjects.
In the present study it was observed that education plays a critical role in suffering hypertension.
Individuals with primary or no education had higher risks of developing hypertension compared to educated subjects (those who had acquired secondary and tertiary levels of education). Similar findings were elucidated by a study conducted by Martins Mpe [23]. BMI in the current study was found to play a major role among South African population who developed hypertension. It was observed that people with high BMI 25 -29.9 -30 and above (overweight and Obese) had higher rates of hypertension compare to those with normal BMI <24.9. This is in contrast to the findings of George et a l [24] where subpopulation groups among Chinese population was assessed for BMI and hypertension, where it was revealed that increased BMI had a positive correlation with hypertension.
This could be attributed to environmental factors and life style as well as ethnicity and other sociodemographic indices.
Alcohol consumption and smoking socio-demographic factors impact and give rise to hypertension as revealed in our study. It was perceived that people with previous and current history of smoking or drinking showed a high rate of hypertension compare to those who never smoke. This result is in consonance with other previous studies conducted in South Africa and other part of the world [24].
The current study demonstrated that participants with chronic diseases have very high rates of hypertension compare to those without chronic diseases. This result is in agreement with other various documented research literature across Africa and other parts of Asia [24]. This could be attributed to many social determinants among the study population.

Hypertension and HIV Status in South Africa/Sub-Saharan
The research findings showed a significant/strong association between hypertension and HIV in both univariate and multivariate analysis, our study further revealed a total dissonance with other similar studies carried out in sub-Saharan countries where some results showed lack of association between hypertension and HIV. In many developed countries, the prevalence of hypertension among HIVpositive individuals varies between 8% and 39%. [19,20]. This is similar to our findings. A study in Kenya reported a lower prevalence of 7.4%-11.2%, [21] compared with 22.1%-32.2% in our study.
These could be ascribed to vigorous nature and athletic exuberance of the East Africans in carrying out physical activities/exercises which results in lower prevalence of hypertension in Kenya [22].

Limitation of the study
The limitations of this research study is associated with the design of the primary project, the

Consent for publication
Not applicable

Availability of data and materials
Data is not restricted, data are contained in the manuscript.

Competing interests
The authors declare that they have no competing interests