ABC | Volume 114, Nº3, March 2020

Original Article Arantes et al. Added salt and blood pressure Arq Bras Cardiol. 2020; 114(3):554-561 CBPmeasurements were obtained by applanation tonometry, using a calibrated and validated device (Sphygmocor®). 12 Each patient refrained from alcohol, coffee and tobacco use for some hours before the exam, which was performed with empty bladder, after a five-minute rest. The variables analyzed from CBP were central systolic blood pressure (cSBP), central diastolic blood pressure (cDBP), central pulse pressure (cPP) and augmentation index (AIx). Collection of the 24-hour urine sample was conducted following the information contained in an explanatory leaflet. The 24-hour urine test was performed at the laboratory of the Federal University of Goias, and an ion-selective membrane was used to quantify urinary sodium at baseline, before the intervention and in the intervals between the visits (total of four collections). During V1B, the NG, PHG and HG received the same instructions regarding the amount of salt intake (6g/day). In visits 2 (V2) and 3 (V3), 5 g/day and 4 g/day of salt, respectively, were given to each participant. Interval between the visits was of 30 ± 7 days. The amount of salt given to each participant was estimated based on the number of people living in the residence and the meals (lunch and dinner) prepared. The salt was delivered properly packed, without weight identification. Also, an additional 10% of salt was given to each participant, to be used in exceptional cases (e.g. visitors at home). In the return visits (V2, V3 and visit 4, V4), all packages of salt were collected and other packages containing the amount of salt planned for the subsequent period were given. In all visits, it was emphasized to participants the importance of cardiovascular health and of a low-sodium diet, and that the amount of added salt consumed by participants should be limited to that established in the study protocol. The salt packages (empty or full) returned were weighed and used for assessment of adherence to the protocol, which was also evaluated by 24-hour urinary excretion. Statistical analysis Statistical analysis was performed using Stata, version 12. An intention-to-treat analysis was used, and for those who dropped out the study before V4, the data of the last visit were considered for analysis. Continuous variables with normal distribution were presented as mean and standard deviation, and those with a non-normal distribution were presented as median and interquartile range. Categorical variables were presented as absolute and relative frequency. Normal distribution of data was tested using the Shapiro-Wilk test. Between-group comparisons in V1A were made using the Kruskal-Wallis test and the Fisher’s exact test. Within-group comparisons before (V1B) and after (V4) intervention were performed by Wilcoxon test or the paired Student’s t-test. Comparison of delta sodium excretion was made by ANOVA followed by Bonferroni post hoc test. Delta sodium excretion was calculated by subtracting sodium excretion at V4 from that obtained in V1B. Correlation between BP (ABPM, and casual and central BP) and the levels of urinary sodium was performed by Spearman’s test. A p < 0.05 was considered statistically significant. Results Fifty-five individuals participated in the study, 32 (58.2%) weremale, median age of 48 years (IQ:39-54). Eighteen (32.7%), 15 (27.3%) and 22 (40.0%) individuals were included in the NG, PHG and HG, respectively. There was no difference in age and sex between the groups, but a significant difference was observed in BMI (p = 0.03) (Table 1). No difference was observed in CBP and AS between V1 and V4 in any of the groups. However, there was a trend of reduction in both cSBP and cDBP from V1 to V4 in all groups (Table 2). There was no difference in delta sodium excretion between the groups (Figure 2). In addition, no differences were found in ABPM, casual BP or urinary sodium from V1B to V4 in NG and PHG (Table 3). Urinary sodium correlated with CPB and peripheral BP in the HG (Table 4). Discussion Based on the methods used for SBP and DBP assessment in the study, the progressive reduction of salt intake was not associated with significant changes in SBP. Also, the authors expected to find a higher sensitivity of CBP in detecting small changes in tension, since this parameter reflects the behavior of more elastic arteries, which did not occur. Data from the literature have associated the reduction in salt intake with a reduction in BP in hypertensive, normotensive and prehypertensive individuals and have shown a higher sensitivity of CBP to detect these changes. However, a large part of these studies was based on interventions or evaluated reductions in the consumption of salt in packaged food and total intake. 18,19 In a systematic review, a mean reduction of 4.4 g/day was associated with a reduction by 2.4mmHg in SBP and 1.0mmHg in DBP in normotensive subjects, and by 5.4 mmHg in SBP and 2.8 mmHg in DBP in hypertensive subjects. These findings indicated a reduction of 0.72 mmHg ad 1.8 mmHg in BP levels in normotensive and hypertensive individuals, respectively, for each gram of salt reduction daily. 18 Improvements in BP levels lead to lower cardiovascular events, including cardiovascular mortality, which reinforces the importance of adopting effective measures to reduce salt consumption. A study conducted in England between 2003 and 2011 evaluated the relationship of reductions in total salt intake with BP and mortality for stroke and acute myocardial infarction and showed a reduction by 2.7 mmHg in SBP and 1.1 mmHg in DBP. Therefore, a fall of BP of 2.7 mmHg led to a decrease in mortality for stroke by 42% and acute myocardial infarction by 40%. 19 In our study, the variables cPP and AIx75% did not show statistically significant reductions, which is in contrast to what the authors expected, since these variables are also related to vascular resistance and arterial stiffness. Again, in our opinion, this may be achieved by an intervention aimed at reducing total salt intake, as previous studies have already demonstrated. 20 In a study conducted with South African hypertensive individuals, the authors evaluated the relationship between salt 556