Design

Primary research articles published between 2011 to 2021 were reviewed and reported using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) framework [16–18]. The time frame of 2011 to 2021 was chosen to critically examine the health promotion interventions that are adopted for the prevention of the risk of hypertension in Africa. This review was conducted from April to August 2021.

Search strategy

We searched six (PubMed, CINAHL, EMBASE, Cochrane library, web of science, google scholar) electronic databases for eligible studies after making scoping searches through manual search guided by the reference list of the selected studies. The key words were first searched in Pubmed, and the corresponding medical subject heading of indexed keywords were identified. The medical subject headings (MeSH) for index words and free text search for non-indexed words were searched by combining the appropriate Boolean operators in the various electronic databases using the advanced search option. In google scholar the first three pages comprising 150 titles were searched manually and appropriate manuscripts were selected. The population, intervention, comparison, and outcome (PICO) framework was integrated in PRISMA in searching, screening, and selecting eligible studies. The population were adolescents and young adults, the intervention was any health promotion intervention, comparisons were not clearly defined, and the outcome was hypertension control [16–18]. The MeSH terms and the free text words and phrases that were searched with the appropriate Boolean operators were (hypertension OR high blood pressure OR elevated blood pressure OR HTN or hypertensive) AND (health promotion OR health education OR patient education) AND (adolescents OR teenagers OR young adults OR teen OR youth). The articles were screened for only African, English-based articles from 2011 through to April 2021.

Search results

In searching from the six electronic databases, 646 titles were identified from using the keywords and 615 titles after duplicates removal. After filtering for only English, published in Africa and within 2011 to 2021, only 615 titles were eligible for abstract and full-text screening. The titles for all these 615 titles were read and screened independently by two of the researchers. Titles that did not focus on health promotion intervention were excluded for full-text screening. The total number of articles selected from this round of screening was 112. abstracts. The full-text of these selected abstracts was screened, and ten articles were deemed to be eligible for this study.

Inclusion and exclusions criteria

The selection of each study depended on predefined inclusion and exclusion criteria. The inclusion criteria took into consideration the following: article focused on a health promotion intervention, study conducted in Africa, published in English and between 2011 through to 2021. The exclusion criteria included articles that measured prevalence and incidence of hypertension, identified comorbidities, and focused on other variables than health promotion intervention.

Data collection and extraction

To extract data, a matrix was first developed, discussed, and agreed on by all the researchers. The matrix guided the way the data was extracted. All the researchers independently extracted data using the matrix. The extracted data were compared and where there was a discrepancy, it was resolved through discussion and consensus. The major variables that were contained in the matrix included. Authors and year of publication, study design, setting, population and sample, data analysis and measurement tool for outcome variables. Other variables extracted were the intervention provider, duration of intervention, name of health promotion intervention and the key findings.

Quality appraisal

The tool used for quality appraisal is the Mixed Methods Appraisal Tool (MMAT) version 2018. Two researchers independently appraised the quality of each study as suggested by Hong et al., 2018 [19]. The appraised data were then compared and where there were discrepancies, it was resolved by consensus. Where a consensus could not be reached, the two researchers consulted a third person, and the majority decision prevailed. The MMAT tool contains methodological criteria for the appraisal of quantitative, qualitative, and mixed methods studies as well as for interventional and experimental studies. The section that was appropriate for the appraisal of the studies was the part that pertains to randomised control trials, non-randomised control trials and mixed methods study. The MMAT tool allowed for screening of each research work by confirming a response of affirmation or disagreement. If there were clear research questions and if the data collection method allowed for the addressing of the research questions. All the studies were affirmative to these screening questions.

The appraisal questions for the section that entailed in randomised control trials section were five and include the appropriateness of randomisation, comparability of groups at baseline, completeness of outcome data, the blindness of assessors and participants adhered to assigned interventions. Only one study was evaluated in this category and had a negative response in respect of the questions that pertained to the blinding of the assessors in respect to the intervention [20]. Five questions were related to the non-randomised control section. These criteria include representativeness of the sample to the population, appropriateness of measurement of both the outcome and the intervention, completeness of outcome data, accounting for confounders in the design and analysis, and whether the interventions were administered as expected. The appraisal showed that some studies did not meet the criteria pertaining to the representativeness of study participants to the population [21–24], presence of complete outcome data [25], accounting for confounders in the design and analysis [22,24,25] and whether an intervention was administered [24]. One of the studies used a mixed-method study design and met all the criteria that include the adequacy of rationale for mixed-method study, appropriate integration of quantitative and qualitative data, divergence, and inconsistencies between quantitative and qualitative results, and that the different levels of the study adhered to the quality criteria of each tradition of the methods used. It did not however meet the criteria for different components of the study effectively integrated to answer the research question [26]. One of the studies was a quantitative study [25] and met all the criteria questions that are stipulated for this section.

Data analysis

The data analysis method that was adopted is convergent synthesis. The convergent synthesis method was used because of the diversity of study designs that were adopted by the primary studies [27,28]. Prior to the synthesis, there was identification and description of the various health promotion interventions that were used for the prevention of hypertension. To use a convergent synthesis analysis method, the study findings were translated into descriptive qualitative sentences [28]. There was then a purposeful collation and integration of the findings [29] into themes from subthemes that were developed from the codes generated. In the views of Pluye and Hong, while conducting this type of synthesis, the various items identified must be integrated into subthemes and similar or related sub-themes collated to form broad umbrella themes [29]. The integration of quantitative and qualitative findings mainly occurred in the coding and development of sub-themes stage [27]. These themes were then described to have meanings that are beyond the originally identified items and hence allow for interpretation and critical analysis. No subgroup analysis and test of the robustness of study finding was conducted as this study was mainly aimed to be a narrative synthesis.

Study characteristics

The study designs adopted were survey [21,25], quasi-experimental [30–32], Cohort [22,24,25], mixed methods [26], randomised control [20], and exploratory uncontrolled pre–post intervention [23] as shown in Table 1. The studies were conducted in the Faculty of Pharmacy at Rhodes University [21], the Gugulethu township of Cape Town [26], Khayelitsha [24] all in South Africa [22,25], Sousse in Tunisia [30], Afon and Ajasse Ipo districts in Kwara State in Nigeria [31], three community pharmacies in the Ashanti Region of Ghana [23], and the slums of Korogocho and Viwandani in Nairobi [30]. The target participants for the health promotion interventions had a minimum age of eleven [21] and a maximum of sixty-five years [30] and included both sexes. The sampling methods adopted were the convenience [21,23,24,26,30], stratified convenience [25], random [30], stratified 2-degree random probability by geographic areas [31], and the Markov model used as a tool for sampling with the focus on age variability of cardiovascular diseases [22]. The study duration for each intervention study ranged from a minimum of a day health education programme [21] to a maximum of 36 months health promotion for behaviour change [30]. The other studies were 3months [25], 4 months [20,26], 5 months [23], 9 to 10 months [25], 12 months [22], 18months [32] and 24 months [24,31] health promotion interventions.

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Table 1. Distributing of study characteristics.

https://doi.org/10.1371/journal.pone.0260411.t001

Reduction in prevalence of hypertension after health promotion interventions

Health promotion interventions were noted to have a positive impact on the prevalence of hypertension [30–32] as shown in key findings in Table 2. The health promotion interventions led to a remarkable decrease in the prevalence of hypertension in the intervention compared to the control groups [30,31]. It was reported that the prevalence of hypertension decreased in the treatment group globally from 37.3% to 33.7% [30]. After stratification for age, for participants younger than 40 years old, a significant decrease in the prevalence of hypertension from 22.8% to 16.2% in the intervention group and 14% to 15.4% in the control group was also noted [30]. A significant decrease in the prevalence of hypertension from 31.4% to 26% was observed among nonobese participants in the intervention group [30].

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Table 2. Distribution of key findings.

https://doi.org/10.1371/journal.pone.0260411.t002

It was also shown that health promotion interventions were noted to improve the intervention group’s ability to control blood pressure [30–32]. The number of respondents with controlled blood pressure increased from 3.0% to 38.8% in the program area, and a lower increase (4.0% to 26.1%) rate was noted in the control group [31]. In instances where there were improvements for hypertension prevalence in both the intervention and the control groups, the changes in the intervention groups were noted to be remarkable [30,32]. Mean blood pressure was said to reduce remarkably in intervention groups than in the control groups [31,32]. There was a significant reduction in mean SBP between baseline and end-line measurements in the intervention (2.75 mmHg) than the control (1.67 mmHg) groups [32]. It was statistically significant that systolic blood pressure decreased by 10.41 mmHg in the intervention, representing a 5.24 mm Hg greater reduction compared with in the control, which showed a decrease of 5.17 mmHg only. Diastolic blood pressure decreased by 4.27 mmHg in the intervention, a 2.16 mmHg greater reduction compared with the control, where blood pressure decreased by 2.11 mmHg [31].

Knowledge increase after health promotion intervention

Health promotion interventions that sought to increase community knowledge on hypertension yielded positive outcomes as knowledge levels were noted to increase [21,23,25]. In a post-intervention quiz, there was a significant increase in the scores from 78.2 to 85.6% in hypertension knowledge among those that received a health promotion intervention [21]. During a post-intervention survey, it was also noted that 40% of the participants reported having heard, read, or seen any food and/or health-related advertisement campaign in the last few months, compared to less than 20% at baseline, across all age and LSM groups [25]. Participants’ awareness of having hypertension in the intervention group was noted to be higher than in the control group [32]. In Ghana, people among the intervention group who were referred to the hospital because they had higher blood pressure (>140/90) did not need to be put on medication [23]. Most of the respondents with hypertension were unaware of their status during the baseline survey but showed significant awareness upon implementation of the intervention [31]. In another health promotion intervention, it was observed that overall knowledge about blood pressure and hypertension increased among those who received treatment [20,26]. It was noted that 40.0% from the intervention group and 17.9% in the control group showed improved knowledge on hypertension [20]. Health promotion on text messaging to hypertension participants on medication adherence was also noted to have a remarkable impact as the treatment arm demonstrated a significantly higher knowledge for an extended duration [26]. In instances where the intervention group was given diaries to use, 97.7% showed it benefited them to remember their medication and clinic appointment [20]. After a media campaign, participants were identified to adopt positive lifestyle modifications (weight loss and no salt or alcohol intake) that reduced their risk of hypertension [25]. After a media campaign for the reduction in salt intake, 77.8% reported that they had seen or heard the specific SaltWatch media campaign that included salt-related health information on TV and radio [25].

Feasibility of health promotion interventions and impact

Community-led health promotion interventions were noted to have a positive impact on people’s adoption of measures to reduce risk or identify early the symptoms of hypertension [22,23,31,32]. It was noted that the community pharmacy is a feasible setting for screening and detection of hypertension if the right structures are put in place [23]. The use of this intervention strategy is also appropriate due to easy accessibility for providing information on lifestyle practices to prevent hypertension [23]. During community intervention programs, newly identified people who have hypertension are referred to the health facility to seek and use professional care [31]. The use of these intervention strategies has led to an increase in the antihypertensive drug treatment from 4.6% to 13.1% among those that were screened- the intervention group [31].

Health promotion interventions reduced hypertension risk factors

Most of the indicators of knowledge, attitudes, and behaviour change showed a statistically significant relationship for the reduction in salt consumption, smoking, alcohol use, and increased physical activity after the administration of an intervention [23,25]. Significantly more participants reported that they were taking steps to control salt intake especially adding salt while cooking and at the table [25]. Given the message that was communicated during the health promotion intervention, the participants could readily remember the key messages that are likely to improve the chance of behaviour change. The most frequently recalled messages were that “too much salt is bad for your health” followed by “you should eat less salt”, these made participants who thought they had consumed the right amount of salt-reduced salt intake [25]. Among patients with hypertension in the control group, smoking and alcohol use were also reduced significantly [32]. It was also noted in Ghana that physical activity levels increase significantly among intervention than in the control groups [23]. It was also noted that there was a significant decrease in the numbers of those reporting inadequate physical activity among the intervention compared with the control group at the population level and among hypertension people at baseline [32].

Cost of health promotion interventions

Community health worker intervention was noted to be cost-effective as it led to a remarkable reduction in the cost of care for hypertension patients [22]. Once the annual cost per patient was below $6.50, the community health worker intervention became “cost-saving” because it saved costs and increased life expectancy, especially when the blood pressure reduction was above 4.98 mmHg [22]. After text messaging, the intervention group had positive increases in self-reported behaviour changes [26]. Health promotion interventions were also noted to produce an improvement in health insurance coverage as the intervention group had a 40.1% increase and the control had less than a percentage point [31]. Self-reported general use of health care resources increased in the program area and decreased in the control area [31].

Strengths and limitations

This study provides a comprehensive overview of the health promotions interventions that are used for the control of hypertension in Africa. It is important to note that all the researchers worked as a team in all the phases of this study, and where there was a disagreement, a consensus was built. This reduced the likelihood of subjectivity that is usually associated with study selection, data extraction, and analysis in systematic reviews. The study is not without limitations as only English-based articles were included in the study, creating the possibility of some salient articles in other languages left out. The protocol for this study did not receive prior registration. Also, the quality assessment of the included studies was minimal as it was largely limited to assessment for only the risk of bias.