Study Population
Among the 1779 subjects aged 25 years and older who were approached, data for hypertension were missing for 2 participants, resulting in a total sample size of 1777 participants, mean age 42.5+16.5 years. Subjects who were 25– 34 years old comprised the largest group (41.0%). Females accounted for more than 60% of this population (Table 1).
The global prevalence of hypertension was 32.9% (584 subjects), with the prevalence of hypertension being similar in men and women (32.8% (228) and 33.0% (356) respectively). General characteristics of our study population are detailed in Table 1. The prevalence of hypertension increased significantly with age (OR: 1.04, p<0.001) (Table 2).
The univariate analysis indicated that increased age, the past or current use of tobacco, increased BMI, sedentary lifestyle, widowed or divorced status, previous occupation other than employee, lower education, animist religion, and increased salt consumption were associated with an increased likelihood of hypertension (Table 2). In the full model (model 3), increased age and BMI, homemade and retired status as well as animist religion remained significantly associated with an increased likelihood of hypertension, whereas the moderate alcohol consumption remained associated with a lower ratio of HTN (Table 2).
Further analyses suggested a higher likelihood of hypertension in the case of high to very high salt consumption and sedentary lifestyle in women as compared to men who seemed less exposed to HTN by a moderate alcohol intake (Table 3). Age, increasing BMI and animist religion remain significant associated HTN factors in both men and women.
Awareness, Treatment, and Control ratios of hypertension
Among hypertensive participants, less than one-half (41.8%) were aware of their condition (Figure 1). Awareness ratios differed between men and women (32.9% vs. 47.5%; p= 0.0039) (Figure 2) and was not influenced by age, education, profession, marital status or income. Female sex was the only associated factor with controlled HTN, independently of the education, occupation, income or marital status (Table 4).
Only 46.3% (113) of hypertensive participants declared receiving antihypertensive treatment at the time of the study (Figure 1). No difference in the prevalence of treatment was observed between men and women (37.3% vs. 50.3%, p= 0.0610), nor in uncontrolled hypertensive (34.1% vs. 35.7%, p= 0.1520). Treatment was not influenced by the socio-economic status.
Discussion
To our knowledge, this population-based study conducted following the STEPS method recommended by the WHO for screening and monitoring risk factors of noncommunicable diseases is the one of the large investigations in the past five years of the prevalence and associated factors of HTN in rural population in West Africa. The study on hypertension conducted in general population in Benin, conducted in 2008, showed an alarming prevalence of 27.9%(8). This condition was highly undiagnosed, as 78% of the subjects were unaware of their high blood pressure. As hypothesized, using the same methodology, our study underlines the highly increased HTN prevalence (32.9%) since 2008 (8). Also, previous data suggested a higher prevalence in urban areas compared to rural zones, explained by the fact that rural African populations were characterized by a traditional lifestyle associating cultural and dietary habits more in favour of HTN prevention (27.1% in rural areas vs 29.5% in urban zones in 2011) (17). Almost twenty years later, our study points out the sociocultural transition in rural areas with a prevalence of HNTN even higher than the prevalence described previously in urban areas. The prevalence of HTN observed in the present study is at the same level as that reported recently in other countries in sub-Saharan Africa: Ghana, Nigeria, South Africa, Sudan and Tanzania (18-20).
The factors generally found to be associated with hypertension include age, BMI, sedentary lifestyle, tobacco use, alcohol consumption. Most of these have previously been identified as important risk factors for hypertension by the different studies conducted in different parts of SSA(21-26). Our results also confirm some of these observed associations such as increasing age, sedentary lifestyle and BMI. The progressive aging of the population with the increase in life expectancy may partially explain the progression of HTN prevalence in Benin.
Our study observed that tobacco users, generally considered at higher risk of CVD were not at higher risk to be hypertensive. This result is probably due to the very low ratio of tobacco use in Benin. Also, alcohol consumption, a well-known risk factor of HTN (14) was not significantly reported in our analyses. In other sub-Saharan African studies results are also controversial, showing either association, or no significant association of HTN and moderate to heavy alcohol consumption(27, 28). Our study suggests a slightly protective effect of the light alcohol consumption in men, probably as the reflect of a healthy lifestyle. All these studies are hardly comparable as they used different settings, and assessments of alcohol consumption.
Recent data show that salt consumption around the world is much higher than is physiologically necessary(29), even more in males than females at any age(30, 31). In a systematic review and meta-regression in 2016 no gender difference was reported in African studies(32). In our study, high salt intake, was independently associated with a higher likelihood of prevalent hypertension. Dietary estimates of sodium intake might not be accurate due to recall bias, reporting errors, erroneous food composition tables (especially if not country-specific or outdated), and/or difficulty in quantifying added salt (e.g. salt added during cooking but discarded in cooking water, etc). However, the fact that there might be a difference between men and women, suggests that context-specific research is needed to establish whether patterns of sodium intake in the SSA settings differ from high-income countries or other low- or middle-income countries.
Our finding regarding higher ratios of HTN in subjects of animist religion are intriguing and we do not find any rational. Further confirmatory and exploratory studies are needed.
In our study, less than 42% of hypertensive participants were aware of their pathology and less than one-half of them took antihypertensive treatments. Among treated subjects, only one-third had controlled hypertension. Few studies have analysed awareness and treatment ratios of hypertension, as well as the fraction with controlled hypertension in Africa(8, 26).
The ratios of awareness and controlled hypertension were higher than other studies on the continent. These differences might be related to variances in socioeconomic levels, healthcare access and preventive measures to reduce HTN. The findings of our study also suggest that independently of the socio-cultural status, women could be more receptive to treatment and more regular during the follow up. This could be explained by a better medical survey for women during and after pregnancy.
Our study has several limitations. Although the definition of hypertension respects the current guidelines, no ambulatory pressures were available. Furthermore, the cross-sectional design of the study, do not allow the assessment of the temporal nature of the associations and survival bias cannot be totally excluded. We also cannot exclude Recall bias cannot be excluded, especially for nutritional factors, but this it is limited since informants were interviewed alongside participants. Also, data on dyslipidaemia were not available and thus were not adjusted for in this study.