Chronic noncommunicable diseases, particularly Cardiovascular Diseases (CVD), are responsible for 63% of deaths worldwide and 72% of deaths in Brazil [1]. Arterial Hypertension (AH) is the main risk factor for global CVD mortality; thus, efforts to reduce cardiovascular morbidity and mortality have focused on the control of Blood Pressure (BP) in patients with hypertension. The prevalence of AH in Brazil is 32.3%, but there are important differences among regions and age groups [2]. Studies in specific populations, such as civil servants of the Longitudinal Study of Adult Health (ELSA-Brazil), have also shown differences in prevalence by education and race/color, with higher values in individuals with lower educational levels and in blacks than in white and brown individuals [3]. However, few studies on this topic have involved indigenous people. A review of local studies, most of which focused on the Amazon region, revealed a highly variable prevalence, mainly because of the degree of acculturation and exchange with the nonindigenous population [4]. Consequently, information on the behavior of BP and its determinants among Brazilian indigenous people is scarce.

Espírito Santo has only one indigenous group living in a demarcated reserve, located in the municipality of Aracruz, on the northern coast of the state. The reserve occupies an area of approximately 18,000 hectares and is home to two indigenous populations with approximately 5,000 people each. Approximately 10% of this population consists of nonindigenous people, and among the indigenous people, 90% are of the Tupiniquim ethnic group, while the other 10% are of the Guarani–Mbyá ethnic group. A study conducted in adults of this population in 2003 through 2004 revealed a prevalence of AH of 20.8% [5], while that specifically in the Guarani population was very low (<5%).

AH is a complex disease whose onset depends on nonmodifiable (family inheritance, sex, age) and modifiable risk factors, especially those related to diet, including salt intake [6,7]. Diets high in sodium and low in potassium increase BP and thus facilitate the development of hypertension [6]. High sodium intake is associated with diets rich in highly processed foods, including ready-to-eat seasonings [8,9]. The current recommendation of the World Health Organization is that salt intake should be limited to 5g/day maximum [10]. The consumption pattern of this nutrient in Brazil is almost double that recommendation, reaching an average value of 9.3g/day, according to the National Health Survey [11].

In a study conducted with the indigenous population of Aracruz (ES) in 2003 through 2004, an average salt intake of 13.7g/day was reported on the basis of sodium measurements in the urine of 12 nocturnal collections [5], a result of the long-standing incorporation of the traditional eating habits of urban populations. The impact of the adoption of Western diets high in sodium by indigenous people has rarely been studied in Brazil. The objective of this study was to determine the profile of sodium and potassium intake in the population of the villages of Aracruz and to verify its impact on the BP of this population.

Of the 1,084 study participants, 36 were excluded because their urine was not collected, and 248 reported being on antihypertensive medication. The data presented correspond to a sample of 800 individuals, among whom 55.4% were women, with a mean age of 37.9±13.4 years. Table 1 shows the sociodemographic and clinical data of the sample, which consisted mostly of young adults (up to 40 years old) and nonsmokers and those who consumed alcohol. In the sample, there was a predominance of Tupiniquins (79.8%) and a lower proportion of Guarani (10.5%) and nonindigenous (10.9%) individuals.

Table 2 shows the clinical characteristics of the sample according to sex. Men had higher mean values of weight, height, SBP and DBP and a higher prevalence of AH and overweight (<0.01), whereas women had higher mean values for BMI, heart rate and prevalence of obesity.

Table 3 shows the urine characteristics of the participants. The concentration of creatinine was higher in males, as were the concentrations of Na and K. The predicted creatinine excretion over 24 hrs, calculated by the Tanaka formula [14], was approximately 18% greater in men (p<0.01). The relationship between the molar concentrations of Na and K in the urine was greater than 3 and similar between the sexes (p>0.05). Only 20 men (5.2%) and 23 women (5.2%) had a Na/K ratio <1, indicating a balanced diet between these two minerals. The estimated salt intake was on average 10.0±2.7g/day and was slightly greater for men than for women (p<0.01). Only 6 women and 2 men reported an estimated daily salt intake within the current recommendation (<5g/day).

Table 4 shows the characteristics of salt intake as a function of sociodemographic and health variables. Consumption was similar across age groups and for different levels of education. It was lower, however, among the Guarani. There was a progressive increase in salt intake as BMI increased. When the eutrophic group was used as a reference (average intake of 9.4g/day), the estimated salt intake was greater in both overweight and obese patients. We detected no difference in salt intake in relation to the presence or absence of AH.

The results of the multivariable regression analysis between salt intake and BP are shown in Figure 1. In the simple correlation analysis, SBP was significantly associated (p<0.05) with age (r=0.468) (r=0.47), BMI (r=0.104) (r=0.07) and salt intake (r=0.100) (r=0.11), whereas DBP was only significantly associated with age (r=0.285) (r=0.28) and BMI (r=0.278). The model including age, BMI and salt intake explained 24% of the total variability in SBP; 22% of the total variability was due to age, while BMI and salt intake each contributed approximately 1% of the total variability. For DBP, the multivariable model that included age and BMI explained 16% of the total variability; specifically, 8% was explained by age and the other 8% by BMI. The same analytical model was used to assess the correlations for SBP and DBP among only the 248 individuals who were using antihypertensive drugs. From a qualitative point of view, the values are the same, but the models lost strength, as age, BMI and salt intake explained 23% of the variability in SBP but only 9% of the variability in DBP.

The main findings of this study are that salt intake by villagers is high, at 10g/day − approximately 2 times higher than the current recommendation − and has a positive effect on SBP values. This impact, however, is small, corresponding to 0.11mmHg/gram of salt in the diet. For DBP, the impact of salt intake was not statistically significant. Considering that salt intake is normally distributed in the population, it can be estimated that almost half of the exposed population has a salt intake above the limit of 10g/day and that only a tiny portion has an intake within the current recommendation of up to 5g/day. The high consumption of salt, combined with the low consumption of fruits and vegetables, which are the main food sources of potassium, resulted in high Na+/K+ ratios in the urine of this population (>3), suggesting a low-quality diet, which contributes to high levels of AH in the community, as well as to other comorbidities, such as overweight, obesity and diabetes, which also contribute to increased blood pressure.

The high values of salt intake observed in this study were also found in the Brazilian adult population in the National Health Survey (2013–2015), where a mean value of 9.7g/day was found using the same technique, i.e., casual urine and calculation of salt intake using the Tanaka formula [16]. The values suggest, therefore, that the mean salt intake in the indigenous population is approximately 10% higher than that in the Brazilian population in general. A previous study conducted in this same indigenous community approximately 20 years ago indicated even higher salt intake (13.7g/day) than that currently reported [5]. However, in the evaluation conducted in 2003/2004, salt consumption was estimated from a 12-hour urine collection at night. Considering that the Tanaka formula underestimates salt intake by approximately 1g/day [15], it can be considered that salt intake in this community is declining slightly, which likely reflects the actions implemented by the government to reduce the salt content in processed foods, the consumption of which is apparently high in the studied population.

This hypothesis is supported by the fact that the mean urine sodium concentration decreased from 154.0±59.7mEq/L in 2003–2004 to 135.7± 58.8mEq/L in 2020–2022 (p<0.001). If we consider water consumption and urine production similar in the two periods, it can be estimated that in the interval between the two studies, there was a reduction of between 1 and 2g in daily salt intake. Notably, a high Na+/K+ ratio is a stronger predictor of cerebral ischemic events than high salt intake is [17]. High levels of salt intake and a high Na+/K+ ratio in casual urine have also been reported in other studies using the same methods of assessment of salt intake used in this study (casual urine [18, 19].

A possible confounding factor in the analysis of the association between salt intake and BP is the fact that overweight and obese individuals consume relatively high amounts of salt, as shown in this and other studies [20]. That is, part of the effect of BMI on blood pressure may be secondary to a diet with higher salt content in these individuals. In the multivariable analysis, however, BMI and salt intake contributed independently to SBP but not to DBP, where excess fat plays an important role in determining higher blood pressure levels, as already demonstrated in several population-based studies [21, 22]. Studies that relate salt intake and blood pressure in populations are well established, such as the one published by Mente et al. [23], in which, in individuals over 55 years, salt intake above 5 g/day was associated with a systolic pressure 2.5mmHg higher than that in individuals whose consumption was lower than 5g/day. A study in the Japanese population indicated that after adjusting for age, sex, BMI and smoking status, each 2.5g/day increase in salt in the diet increased the systolic blood pressure by 0.9mmHg [24], which is greater than that reported in our study, where adjustment for age or BMI showed an increase of 0.11mmHg/g of salt, which was identical to that following adjustment for both age and BMI. The impact of salt intake on blood pressure, however, does not seem to be uniform, because this association was not found in the Vietnamese population after adjustment for age, smoking status and alcohol consumption [25]. A possible reason for these apparently nonuniform results could be that the blood pressure in different populations could have different degrees of sensitivity to salt. If this is the case, the indigenous population could present a lower blood pressure response to salt than other populations for whom sensitivity to salt would be greater. Notably, our sample includes a small portion (approximately 10%) of nonindigenous people. However, the exclusion of this group from the analyses did not affect the results (data not shown). Alternatively, the greater or lesser impact of salt intake on blood pressure may be due to the intake of other nutrients, such as K+, and the efficiency of pressure diuresis, whereby a higher sodium intake would lead, at first, to greater water intake and increased extracellular volume, followed by stimulation of diuresis, causing the body to eliminate the excess sodium ingested [26,27]. In such cases, increased salt intake would not contribute to increased extracellular volumes or, consequently, to increased blood pressure. The lack of association between salt intake and diastolic pressure is because fat accumulation, and not extracellular volume, is the most important factor in its determination [28,29].

The high salt intake observed in this study is due to the adoption of westernized eating habits by indigenous populations. The community that inhabits the Aracruz reserve does not function as a closed community but is open and has a high degree of interaction with the rural and urban surroundings of the municipality of Aracruz. Approximately 20% of adults are regularly employed in the public or private sector, and food is purchased in regular commercial establishments, such as bakeries and supermarkets, some of which exist within the reserve itself. Although they live in a rural area, the cultivation of food for their own consumption (including vegetables and fruits) is very rare, resulting in a low-quality diet profile that results in a high Na+/K+ ratio in the urine due to the consumption of processed and ultra-processed foods, which currently account for 30% of the diet of the Brazilian population [30].

Excess body fat is closely related to increased blood pressure. In this study, we clearly showed that overweight and obese individuals have higher salt intake. Multivariable analysis revealed that both factors contribute to increased systolic blood pressure. Thus, high salt intake contributes, albeit indirectly, to the onset of metabolic syndrome and insulin resistance and, consequently, type 2 diabetes [28,31], which was also highly prevalent in this population. It should be noted, however, that the prevalence of hypertension and diabetes described in this study are underestimated with respect to the actual prevalence of these conditions in the study population because, in order to relate pressure to salt intake, all individuals who were using antihypertensive drugs, many of whom also have diabetes, were excluded from the analysis.

Our study has several limitations, including the lack of evaluation of sodium excretion by the method considered the gold standard, 24-hrs urinary excretion. However, estimation of salt intake from the Na+/creatinine ratio in casual urine is easier to perform in large population groups, as previously reported in population-based studies in Brazil, including the National Health Survey [16]. The Tanaka formula, in turn, is adequate for estimating the average consumption in a group of individuals but is inadequate for accurately estimating individual consumption [14,15]. The validity of the application of this formula was tested in an urban population in the same age group as the sample in the current study, and it showed adequate performance with respect to 24-hour urine collection [15]. Given the cross-sectional nature of the current study, it is not possible to establish a cause and effect relationship. Another point to be considered is that the study was conducted on volunteers and not on a random sample of the population. However, the project covered approximately 37% of the entire population eligible for the study, and the demographic data of the sample are similar to those of the population as a whole in terms of age groups. There was a predominance of women, as is common in studies with volunteer samples. The adjustment for sex in the regression analyses did not affect the quality of the analytical model or the conclusions. Therefore, it can be inferred that the study data are representative of the population of the villages and should reflect, to a large extent, the characteristics of the indigenous population in view of the large predominance of this segment in the sample studied.

Salt intake in the indigenous population of Aracruz is high, with an average of 10g/day, double the recommended value established by the World Health Organization (5g/day). Although the association between salt intake and SBP was statistically significant, the observed impact was modest, with an increase of 0.11mmHg for each gram of salt consumed. This effect was more strongly observed in overweight and obese individuals, suggesting a complex interaction among diet and risk factors for hypertension. Additionally, the high Na/K ratio observed indicates a low-quality diet characterized by excessive consumption of processed and ultraprocessed foods, which contributes to the high prevalence of hypertension and other comorbidities, such as type 2 diabetes.

Nutritional education programs that address the importance of a balanced diet and a reduction in salt intake, as well as the continuous monitoring of blood pressure and eating habits of the indigenous population, should be implemented. In addition, public health policies should be promoted to encourage the production and consumption of fresh and healthy foods to reduce dependence on industrialized products. This integrated approach could contribute to mitigating the risks associated with excessive salt intake and promoting cardiovascular health in the indigenous population of Aracruz.