Hypertension is the leading cause of cardiovascular diseases (CVDs) morbidity and mortality worldwide [1] and it has an increasing prevalence in most of sub-Saharan Africa (SSA) countries [2, 3]. However, in SSA, there is marked regional variation in the prevalence of hypertension with rates between 15 and 70% [3‐6]. In Cameroon, as in several African countries, the prevalence of hypertension is higher in urban than rural regions [7, 8]. This is attributed to the effects of globalization and urbanization which stimulate unhealthy behavioral changes [4, 7‐10]. Causal factors for high blood pressure (BP) associated with the rural to urban migration are: reduced physical activity, stress, and modified diets with increased consumption of salt [7‐11]. High dietary salt increases BP and is a leading cause of hypertension [12‐16]. Conversely, an increase in dietary potassium reduces BP and attenuates the hypertensive effect of high dietary salt [13].

Few studies have been published on salt consumption in SSA with most available data suggesting a lower intake of salt than in other continents [13‐17]. However, some research support a greater impact of high dietary salt on BP in SSA, as the black African ancestry populations are more salt sensitive [16, 18]. Globally, a lack of high quality studies creates uncertainty about the overall impact of dietary salt on the health of African peoples [16].

In most of African countries, much of the dietary salt comes from commercial sources [19]. Therefore, some rural hunter–gatherer populations such as Pygmies, who primarily eat foods from natural sources with their staple diet including mainly complex carbohydrates, fruits, vegetables and bushmeat, would be expected to have low levels of salt intake since they would not be exposed to salt widely and inexpensively available from commercial sources as is the case for bantus living in urban environment.

Pygmies are nomadic and are the largest group of mobile hunter-gatherers of Africa [20]. Limited data indicate that Pygmy hunter-gatherer populations are relatively free of CVDs [21] and of their risk factors as well [21‐23]. This study aimed to examine association of urinary sodium with BP and factors associated with hypertension among Cameroonian pygmies under hunter-gatherer subsistence mode and Bantus, living separately in urban area under modern unhealthy behavioral habits.

About 21 Bantu participants in Douala and 16 pygmy participants in Lolodorf refused to participate to survey. A total of 150 hunter-gatherer rural pygmies and 150 urban Bantus were finally included in the present survey (Table1). The survey participation rates in Douala and lolodorf were 87.7% and 90.4%, respectively.

The pygmies were older and shorter than the Bantus (all p <  0.001). Overall, there were more men than women participants, however the sex ratio did not differ significantly between pygmy and Bantu dwellers (p > 0.05) (Tables 1 and 2). Educational level, overweight/obesity and abdominal obesity rates, SBP and DBP, MAP and PP were lower in pygmies than in Bantus (all p <  0.01). Tobacco use rate in Bantus was 5.4% and was not significantly different from that of pygmies (6.7%). The age-adjusted prevalence of hypertension was markedly lower in pygmy than in Bantu participants: 3.3% vs 28% respectively; p <  0.0001 (Table 1). Pygmy hypertensive participants were newly diagnosed for high BP and were not under antihypertensive medication. Only 18% of all Bantu hypertensive patients of the current study were under antihypertensive medication, of whom 95% reported taking regularly calcium antagonists, while 5% of them were under alpha-methyldopa. Neither calcium channel blockers, nor alpha-methyldopa influence urinary sodium excretion when taken chronically. According to WHO recommendations on physical activity, only 23% of Bantu dwellers were physically active. Heavy alcohol consumption rate was high in the both two study groups, however, it magnitude was more pronounced in Bantu than in pygmy participants (66.7% vs 52%, p = 0.014). Urinary sodium excretion was more than twice lower in Pygmies than in Bantus (p <  0.0001). By contrast, potassium urinary excretion was similar between the two groups (p = 0.3). The sodium to potassium excretion ratio was lower in the pygmies than in the Bantus (p <  0.0001) (Tables 1 and 2).

In this cross-sectional study, we have found marked differences in blood pressure and prevalence of hypertension between Cameroonian pygmies and Bantus. In keeping with the mean high BP and higher prevalence of hypertension in Bantus relative to Pygmies, we found that urinary sodium excretion, alcohol consumption, overweight/obesity, physical inactivity and visceral obesity were also elevated in Bantus, while urinary potassium excretion was similar. Furthermore, we found that sodium excretion was significantly greater in hypertensive than normotensive participants in the Bantus group. This was not the case in pygmies where hypertension was uncommon, urinary sodium much lower and blood pressure increased little with age. Importantly, multivariate logistic regression analysis revealed urinary sodium excretion as an independent determinant of hypertension in the whole study group.

High sodium intakes are related to salt added to commercial foods or that added during food preparation [32, 33]. Pygmies have retained a hunter-gatherer existence. Their diet consists of about 50% meat and 50% plant and fruits and therefore, their main source of sodium is meat [34]. As in our study, Kesteloot et al. [23] has previously demonstrated that sodium excretion was higher in Bantus than pygmies of southern Cameroon. Conversely, urban dwellers consume more salty foods depending on the level of urbanization and the type of population. Indeed, in a study conducted by Tayo et al. [35], among three different black populations, sodium excretion increased across the east-west gradient (e.g., 123 ± 54.6, 134.1 ± 48.8, 176.6 ± 71.0 mmol/L, Nigeria, Jamaica and US, respectively). This east-west gradient is related to the gradient of development between those three countries. This is consistent with the relation between urbanization, nutritional habits and CVDs [11, 35, 36].

We found that sodium excretion was higher in hypertensive than in normotensive participants in the whole study population. When separated into pygmies and Bantus, sodium excretion remained higher in hypertensive than in normotensive Bantus, while the difference was not significant in pygmies. Our observations are consistent with a greater frequency of salt sensitivity previously reported in black hypertensive patients [16, 37, 38]. Furthermore, when adjusted for age, BMI and WC, sodium concentration was significantly and positively correlated with systolic BP, diastolic BP and MBP in the whole study population and in the Bantus group, but not in the Pygmies. These findings are consistent with the known impact of high dietary salt on blood pressure and hypertension [13, 14]. The lack of correlation between blood pressure and sodium excretion could be explained by the low sodium excretion observed in Pygmies. In the international study of electrolyte excretion and blood pressure (INTERSALT), populations with very low sodium consumption (0.2–51.3 mmol/24 h) had a low blood pressure compared to other populations and a slow increase in blood pressure with age [15]. It has been hypothesized that low sodium intakes may reduce the rise in blood pressure upon aging [15, 16].

In our study, we confirm that nearly all the cardiovascular risk factors (hypertension, abdominal obesity, overweight and obesity), as well as their indicative parameters (BP, BMI, WC) were higher in Bantus than in pygmies [21, 23, 28, 39]. Pygmies are nomadic, moving periodically inside the African forest. They have legendary good aerobic fitness, with low body fat and low prevalence of obesity, and low blood cholesterol levels [21, 22, 40]. Moreover, the hunter-gatherer subsistence living of pygmies is hypothesized as one of the key factors involved in their lesser rise in arterial stiffness with aging [21]. Another consequence of the hunter-gatherer lifestyle is a slower increase in blood pressure with aging, as we have observed. A change in the lifestyle can lead to the development of cardiovascular risk factors, as previously observed on Kalahari Bushmen community by Tichelaar et al. [41], as well as in the Kenyan Luo community by Poulter et al. [9]. Otherwise, not all aboriginal communities express a good cardiovascular health. In the indigenous Maori community in New Zealand, CVD is more prevalent in rural Maori in comparison to urban Maori and to non-Maories [42]. These opposite results emphasize the impact of genetic characteristics in the involvement of CVDs [42] and may play an important role in the populations which we investigated. This will require further studies.

Globally, the observed low rate of cardiovascular risk factors among pygmies, contrasting with their high burden in Bantus, suggests the influence of living environments rather than genetic determinants in the development of the increasing burden of hypertension and CVDs in Cameroon. A major factor underlying the increase in CVDs in Bantus, and globally in other Cameroonian populations is rapid and uncontrolled urbanization, which is a driving force for most of the modifiable risk factors such as obesity, hypertension, reduced physical activity, high salt diet, sarcopenia, and increased tobacco and alcohol consumption [4, 7‐10, 43, 44]. This survey findings outline the essence of our hunter-gatherer lifestyle and suggest the need to re-align our modern milieu with our traditional lifestyle to improve cardiovascular health. This includes intense lifestyle education, with emphasis on reduced dietary salt intake, more balanced and diversified diets and regular cardiovascular risk factors screening. Our findings also increase knowledge of the health status of pygmies in a country lacking health data and provide strong arguments to policy-decision maker to implement strategies and solutions that combine ecosystem management and adequate health-sector interventions to improve human health and well-being while maintaining a healthy ecosystem.

There are some limitations to our study. First, because cultural, traditional and economic constraints, it was not considered feasible to collect 24 h urine samples to assess sodium and potassium excretion. Other rather recommend instead using a series of 24 h-urine sodium samples since, in general, 6–10 samples of 24 h urine are required to accurately estimate usual salt intake in an individual. Casual urine samples to assess usual dietary sodium is a frail method given most dietary sodium is excreted within 6 h of ingestion and that in many populations; sodium intake varies markedly between meals and days. In Pygmies, diets are relatively constant without large variation in salt contents of foods. Hence a casual urine sample for sodium might be more accurate in Pygmies than in Bantus with highly varied food intake. In mitigation, averaging sodium excretion based on a casual morning overnight urinary sodium excretion samples from a representative large sample of the diverse worldwide population, appeared a reasonable reflection of the population’s average dietary sodium. The second limitation of the present study is the lack of assessing and comparing the CVDs risk factors in hunter-gatherer rural Bantus and hunter-gatherer rural pygmies. This may have helped to better understand CVDs risk factors beyond environmental, behavioral and dietary risk factors such as genetics differences between Bantu and pygmies. Moreover, our survey sample size was small and may not be representative of all Cameroonian pygmy and Bantu communities living in both rural and urban regions of Cameroon. Thus, we cannot rule out the possibility that participants in the study, as well the association with urinary sodium with BP and hypertension, could differ from a broader and more heterogeneous Cameroonian population. Therefore, caution should be exercised when extrapolating our estimates to a broader population in the same and other settings in Cameroon. The third limitation of the survey is that we could not assess the level of physical activity in pygmies using the same criteria as in Bantus. Thus, it could have not been possible to determine the real impact of physical activity on blood pressure and hypertension risk in the whole study population. In mitigation however, we used a multilevel cluster sampling methodology which we believe is an important methodological strength of our study. Importantly, we have further used standardized measurement procedures to collect data in an accurate and reproducible way and used robust analytic methods to generate estimates that will facilitate comparisons with evidence from elsewhere.

The present study demonstrates that hunter-gatherer living is associated with low level of urinary sodium excretion, which is associated with a low rate of hypertension and a slower increase of blood pressure with age in traditional pygmies. Importantly, high salt diet was an independent driver of high blood pressure in our study population. Our findings underscore the need of public health efforts to implement cost-effective community-based prevention programs to promote risk factors screening campaigns and healthier lifestyles including strategies for reduction of dietary sodium intake to curb the development of hypertension and other non-communicable diseases in Cameroonian.