Association between salt taste sensitivity threshold and blood pressure in healthy individuals: a cross-sectional study

ABSTRACT BACKGROUND: Hypertension is an important public health problem. Overweight and high salt intake are risk factors for its development. OBJECTIVE: To evaluate the association between salt taste sensitivity threshold (STST) and blood pressure (BP) in healthy adults. DESIGN AND SETTING: Cross-sectional study conducted in a private institution. METHODS: 104 healthy adults (aged 18-59 years) were evaluated. Sociodemographic, clinical and dietary data were collected. Nutritional status and BP were assessed using body mass index (BMI), waist circumference (WC), systolic blood pressure (SBP) and diastolic blood pressure (DBP). STST was assessed using graded saline solutions with sodium chloride concentrations ranging from 0.228 to 58.44 g/l. Identification of salty taste in solutions ≥ 3.652 g/l was used as the cutoff point for high STST. RESULTS: Participants with high STST presented higher daily average intakes for energy (2017.4 ± 641.5 versus 1650.5 ± 357.7 kcal/day; P = 0.01) and sodium (3070.2 ± 1195.1 versus 2435.2 ± 963.6 mg/day; P = 0.01) and higher BMI (P = 0.008) and WC (P = 0.002). After adjustment for age, sex, sodium and potassium intake, WC and family history of hypertension, the averages for SBP and DBP in subjects with high STST were higher than in those with normal STST (SBP: 138.2 ± 1.7 versus 119.7 ± 0.9 mmHg; P < 0.001; DBP: 81.2 ± 1.9 versus 75.1 ± 1.0 mmHg; P = 0.008). CONCLUSION: High STST was associated with elevated blood pressure in healthy adults, regardless of other risk factors for hypertension.


INTRODUCTION
Hypertension is a multifactorial clinical condition in which the prevalence differs according to the ethnicity and age group of the population evaluated. 1 The genesis of hypertension involves a number of well-described factors, such as inadequate diet (high amounts of dietary sodium and low potassium intake) and excess adiposity. 2,3 However, the organic response to sodium overload is a mechanism that deserves attention. 4 Epidemiological studies have suggested that susceptible individuals present elevated blood pressure (BP) through high sodium intake. 5,6 Salt sensitivity is influenced by genetic factors, and not all the population seems to benefit from severe sodium restriction. 7 Meta-analyses and longitudinal studies have suggested that, in comparison with adequate salt intake (4 to 5 g/day), very low sodium intake is associated with increased mortality and cardiovascular events. 8,9 In addition to age and ethnicity, the status of BP levels (normal or elevated/hypertension) seems to be a determinant of the organic response to saline intake. 10 The salt taste sensitivity threshold (STST) consists of the individual's ability to recognize the taste of sodium. Taste sensitivity decreases according to age and it has been observed that this decrease begins when individuals are around 20 years old. 11 A high STST suggests that the individual is more likely to have excessive salt intake; on the contrary, a normal STST defines that the individual is more likely to have low salt intake. It has been speculated that hypertensive individuals have greater STST than normotensive individuals, which would contribute towards higher sodium intake and, consequently, elevation of BP. 12 Although the evidence suggests that very low salt intake may contribute negatively to cardiovascular outcomes, reducing sodium intake is still an important public health recommendation as a preventive measure against the incidence of hypertension and as therapy for those who and clinical information, including known previous diseases and family history of hypertension (father, mother and grandparents).
To verify the frequency of consumption of food rich in sodium, a specific food frequency questionnaire (FFQ) was used. The instrument asked about 15 foods, and the participants reported the frequency of consumption of each of them, on linear scales marked out as follows: 1 -I never eat this; 2 -I eat this less than once a month; 3 -I eat this one to three times a month; 4 -I eat this once a week; 5 -I eat this two to four times a week; 6 -I eat this once a day; or 7 -I eat this twice or more per day. This questionnaire was developed among low-income Brazilian hypertensive patients and its reliability and validity were tested in the same population. 15 In addition to the FFQ, a 24-hour food recall (R24h) was used.
In this method, the participants reported all types and quantities of  ily history of hypertension, sodium intake and potassium intake.
The significance level was taken to be 5%.

RESULTS
The average age of the participants was 28.6 ± 7.4 years; 80.8% were female and 98% were self-reportedly of white ethnicity.   = 0.01) than that of the subjects with normal STST. There was no significant difference in relation to potassium consumption. The BMI of the individuals with high STST was significantly higher than that of the individuals with normal STST (P = 0.008), and this was also found in relation to WC (P = 0.002).
In evaluating the consumption of foods with high sodium content in the entire sample, ham, sausage, pizza and snacks had the highest frequencies, as shown in Figure 1. However, no differences were observed in the averages for SBP and DBP in relation to the frequency of consumption of foods with high sodium content. There was also no difference regarding the classification of salt taste sensitivity (normal or high) in relation to the frequency of consumption of these foods (data not shown).

DISCUSSION
In our study, we observed an association between STST and BP levels among young adults of primarily Caucasian origin, regardless of other factors relating to BP elevation, such as age, sex, sodium and potassium intake, WC and family history of hypertension. We also, as expected, identified positive correlations between BP and obesity indicators. Moreover, we observed higher energy and sodium intake among participants with high STST, as well as higher BMI and higher WC. We did not identify any difference in relation to the presence of a family history of hypertension, according to STST status. In addition, there was no difference in SBP and DBP values in relation to the presence or absence of a family history of hypertension.
In Indian adolescents, higher STST and higher BP levels were observed in individuals with a family history of hypertension. 19 It is known that there is a genetic predisposition associated with salt taste perception and that certain populations are genetically more susceptible to development of hypertension. 20,21 Thus, these conditions may be genetically connected, but this association needs to be better explored. 22 The relationship between excess adiposity and sodium intake has been explored. In our study, we identified that both the BMI and the WC of participants with high STST were significantly higher than in those with normal STST, as also was dietary sodium Table 3. Adjusted means for arterial blood pressure according to the salt taste sensitivity threshold classification (mean ± standard error; n = 104)   intake. Some authors have identified a positive association between high sodium intake (detected through 24-hour urinary excretion) and changes in body composition in Caucasian populations, with increased body fat and decreased lean mass, regardless of energy intake. 23 Other authors have shown that, for each additional 1 g of ingested salt, the chance of developing obesity is about 26%, regardless of energy intake and ethnicity. 24 Obese individuals have lower STST than do non-obese individuals. 25 However, salt intake appears to be higher among overweight children and adults than among those with normal body mass. 24 High sodium intake can lead to increased food and energy intake, and it may replace the satiety effect promoted by dietary fats. 26 In our study, we identified higher energy intake among par- contributing towards reduction of appetite and food intake). 28 In animal models, high sodium intake increases endogenous production of fructose, thereby triggering the processes of leptin resistance and hyperphagia, which result in obesity, insulin resistance and hepatic steatosis among mice. 29 Differently from Antonello et al., who also evaluated a population in southern Brazil, 30 we observed in our study that there was a significant association between STST and BP levels. Our results are in agreement with other studies conducted among different populations. [31][32][33] However, there are some controversies regarding the relationship between the salt taste threshold and BP status: in some studies, patients with hypertension have shown a higher recognition threshold for salt, 30,34 while in others it was concluded that there was no difference in STST between people with and without hypertension. 35,36 Studies evaluating potential associations between STST and health outcomes are still scarce and quite heterogeneous regarding the type of design used, the methods used to identify BP levels and sodium intake, the type of population and the number of participants evaluated, which makes it difficult to compare the results.
Among the limitations of this study, we can mention the crosssectional design, which may have presented the bias of reverse causality; the lack of quantification of urinary sodium and nonperformance of 24-hour ambulatory blood pressure monitoring (ABPM); the application of a one-day 24-hour recall, which might not have accurately reflected the dietary habits of the sample (it may underestimate or overestimate food intake, or may characterize flat-slope syndrome); no information about the participants' levels of physical activity was obtained (this is an important factor associated with BP levels); and most of the participants in the study were Caucasians and showed high education levels.
Conversely, we can highlight that our study represented "real life", since ABPM and urinary analysis are not always widely available in clinical practice. Furthermore, we tried to perform analyses that were adjusted for a range of confounding factors that have been correlated with BP changes.

CONCLUSION
An association between STST and BP was observed among the healthy adults participating in this study, regardless of other risk factors for elevation of BP levels, such as age, nutritional status and micronutrient intake. In addition, we identified that the energy and sodium intakes were higher among participants with high STST, and these individuals' BMI and WC were also higher.
This result emphasizes the importance of preventive interventions for lifestyle changes, in order to avoid the development of hypertension and other chronic non-communicable diseases.