Journal of the American Society of Hypertension 8(4) (2014) 232–238
Research Article
High potassium intake blunts the effect of elevated sodium intake on blood pressure levels Sergio Lam^ego Rodrigues, MD, PhDa,*, Marcelo Perim Baldo, PhDa, Rebeca Caldeira Machado, MSca, Ludimila Forechi, MSca, Maria del Carmem Bisi Molina, PhDb, and Jose Geraldo Mill, MD, PhDa a
Department of Physiological Sciences, Federal University of Espırito Santo, 29042-755 Vit oria, Brazil; and b Department of Nutrition, Federal University of Espırito Santo, 29042-755 Vit oria, Brazil Manuscript received November 30, 2013 and accepted January 2, 2014
Abstract The purpose of this study was to investigate the influence of dietary potassium on the sodium effect on blood pressure (BP) in the general population and the adherence of current recommendations for sodium and potassium intake. An overnight (12-hour) urine sample was collected in a population-based study to investigate cardiovascular risk. A sub-sample of 1285 subjects (age range, 25–64 years) free from any medication interfering with BP or potassium excretion was studied. Of the participants, 86.0% consumed over 6 g of salt/day and 87.7% less than the recommended intake of potassium (4.7 g). Potassium excretion and the sodium to potassium ratio were significantly related to systolic and diastolic BP only in subjects consuming more than 6 g/day of salt. Subjects in the highest sodium to potassium ratio quartile (surrogate of unhealthy diet) presented 8 mm Hg and 7 mm Hg higher values of systolic and diastolic BP, respectively, when compared with the first quartile, while individuals in the fourth quartile of urinary potassium excretion (healthier diet) showed 6 mm Hg and 4 mm Hg lower systolic and diastolic BP, respectively, compared with the first quartile. Our data indicate that when people have an increased intake of potassium, high intake of sodium is not associated with higher BP. J Am Soc Hypertens 2014;8(4):232–238. Ó 2014 American Society of Hypertension. All rights reserved. Keywords: Blood pressure; potassium; sodium; hypertension.
Introduction Reduction of the intake of sodium has been established as a lifestyle change recommended to reduce cardiovascular diseases (CVD) mainly by decreasing blood pressure (BP) levels.1 Recently, the relationship between mortality and usual intake of sodium and potassium in American adults was reported. Higher intake of sodium was associated with increased overall mortality. Moreover, diets with
This study was supported with grants from CNPq (No. 302296/2008-5 and No. 561959/2010-2) and FINEP (No. 01 06 0300.00 ES). Disclosures: The authors declare no conflict of interest. *Corresponding author: Sergio Lam^ego Rodrigues, MD, PhD, Department of Physiological Sciences, Federal University of Espirito Santo, Av. Marechal Campos, 1468–29042-755, Vit oria, ES, Brazil. Tel.: þ55 27 33357335; fax: þ55 27 33357330. E-mail: [email protected]
higher sodium to potassium ratio (Na/K) were associated with increased risk of CVD and all-cause mortality.2 Diets with elevated content of sodium or increased Na/K ratio are related to increased BP and higher prevalence of hypertension.3,4 Hypertension is a major risk factor for several CVD including stroke, cardiac arrhythmias, heart failure, sudden cardiac death and chronic kidney disease.5 Therefore, it is not surprising that hypertension is present in around 69% of patients with the first myocardial infarction and around in 77% of patients with the first stroke.6 The association between the intake of sodium and hypertension is well established.2,3,7,8 However, the potential role of the intake of potassium to cardiovascular health has received less attention. It was reported that the intake of potassium estimated by food records was not independently associated with blood pressure.9 Conversely, two population-based studies showed that potassium intake— assessed by semi quantitative food frequency questionnaire10 or 24-hour recall dietary history11—was inversely
1933-1711/$ - see front matter Ó 2014 American Society of Hypertension. All rights reserved. http://dx.doi.org/10.1016/j.jash.2014.01.001
S.L. Rodrigues et al. / Journal of the American Society of Hypertension 8(4) (2014) 232–238
related to both diastolic BP (DBP) and systolic BP (SBP). Reports on interventional studies have also shown an inverse relation between potassium intake and BP. However, these studies were based on the use of potassium supplementation and/or controlled diets.12–17 It is worth mentioning that diet in interventional studies provides larger amounts of potassium, calcium, and magnesium than the typical diet, which can be a factor of confusion.18 Despite the elevated prevalence of hypertension associated with high salt consumption (around 12.8 g/day) in the Brazilian population,7 to date, there is scarce information regarding the influence of potassium intake on BP in the general population. Accordingly, a recent report on potassium intake and the estimated potential impact of increased potassium intake on population BP levels included 21 countries spread across North America, Europe, Asia, and Oceania, but South America in general and Brazil in particular.19 Therefore, the aim of this investigation was to estimate the influence of dietary potassium intake on the sodium effect on BP levels in the general population free from the influence of any medication interfering with blood pressure or potassium excretion and also to determine the adherence of the participants to the current recommendations for sodium and potassium intake.20
233
Anthropometric parameters were obtained by trained technicians. Body weight was taken on an electronic balance (Toledo, Brazil) and height in a wall-mounted stadiometer (Seca, Germany). Body mass index (BMI) was calculated as body weight (kg) to the squared height (m2). Waist circumference (WC) was measured at the mean point between the lowest rib margin and the iliac crest with the participant standing and at the maximum point of normal expiration. Smoking was considered present if the subject declared current use of tobacco cigarettes or pipe.
Sodium and Potassium Consumption
Data were collected to determine the prevalence and severity of cardiovascular risk factors in the urban population of Vitoria, Brazil. The design and sampling of this survey was described elsewhere.7,21 Briefly, a sample of 1661 individuals was selected by a procedure of household randomization. These individuals attended University Hospital to undergo clinical and laboratory exams to determine presence of cardiovascular risk factors. The project was approved by the Institutional Ethics Committee, and all participants gave informed written consent.
All participants received personal instructions at home about overnight urine collection. All urine produced during a 12-hour period (7:00 pm to 7:00 am) during the night preceding the clinic visit was collected in sterile plastic bottles. Participants were asked to record the time of the last void in the toilet before starting urine collection as well as the exact time of the last void in the bottle in the morning of clinic visit. At arriving on the clinic, the participants’ annotations were analyzed, and they were thoroughly questioned about the completeness. The validity of the urine as representative of a 12-hour period was accepted if the collect period ranged from 11 to 13 hours and if urine volume was 250 mL. From the original sample of 1661 subjects, 376 were excluded from the present analysis, because urine was not collected (n ¼ 10), urinary volume was 1.4 mg/dL (n ¼ 52), or there was use of antihypertensive drugs, including diuretics (n ¼ 270). Therefore, data are related to 1285 subjects (613 men and 672 women), free from the influence of any medication interfering with BP or potassium excretion. The daily sodium and potassium intake was estimated considering that 47% and 39%, respectively, of the 24hour total excretion on these substances in urine occurs during the night period (7:00 pm to 7:00 am)22 and that 77% of dietary potassium is excreted in urine.23 Salt consumption was estimated considering all sodium ingested as NaCl.22
Measurements
Statistical Analysis
Participants attended to the clinic at morning after 10 to 14 hours of fasting. BP was measured in the sitting position by using a standard mercury sphygmomanometer on the left arm after a 5 to 10 minute rest period. Mean values of SBP and DBP were calculated from two readings carried out by two independent trained staff members. Participants were considered hypertensive in presence of BP 140/ 90 mm Hg or when using antihypertensive drugs. A fasting venous blood sample was collected from each participant to determine glucose, creatinine, and lipids, by using validated commercial kits. Diabetes was defined in presence of fasting glucose >125 mg/dL or use of hypoglycemiants.
Statistical analysis was carried out using SPSS 18.0 (Chicago, IL, USA). Data were described as means standard deviation for continuous variables and proportions to categorical values. The goodness to fit to normal distribution was evaluated using the Kolmogorov–Smirnov test. Participants were divided by quartiles based on their 12-hour urinary potassium (urK) excretion and urinary sodium to potassium excretion ratio (urNa/K). Analysis of variance was used to compare means of continuous variables and the c2 test for categorical variables. Analysis of covariance was used to adjust for age, BMI, and urinary creatinine excretion (urCr). BMI, triglycerides, and urinary sodium
Methods Study Design and Sample Selection
234
S.L. Rodrigues et al. / Journal of the American Society of Hypertension 8(4) (2014) 232–238
Table 1 Baseline characteristics of the sample according to gender Variable
All Subjects (1285)
Age (years) SBP (mm Hg) DBP (mm Hg) BMI (kg/m2) Waist circumference (cm) Cholesterol (mg/dL) Triglycerides (mg/dL) HDL-c (mg/dL) Glucose (mg/dL) Creatinine (mg/dL) Salt intake (g/day) Potassium intake (g) Obesity (%) Arterial hypertension (%) Diabetes mellitus (%) Smoking (%)
43 124 82 25.7 85 212 134 45 102 0.97 12.9 2.9 15.5 31.0 5.3 25.2
Men (613)
10 (43) 192 (122) 13 (81) 5 (25) 12 (84) 47 (206) 133 (100) 13 (44) 27 (97) 0.2 (1.0) 7.4 (11.5) 1.8 (2.5)
44 128 86 25.6 88 213 160 42 104 1.0 14.0 3.2 13.8 41.1 6.2 29.1
P
Women (672)
11 (43) 18 (126) 13 (85) 4 (25) 11 (88) 51 (206) 169 (121) 12 (40) 27 (91) 0.2 (1.1) 7.0 (13) 1.9 (2.7)
43 120 79 25.8 81 211 109 49 100 0.87 12.0 2.7 17.0 21.7 4.5 22.3
10 (43) 20 (118) 12 (78) 5 (25) 12 (80) 43 (206) 81 (90) 12 (48) 26 (96) 0.2 (0.9) 6.0 (5) 1.8 (2.4)
.33
Research Article
High potassium intake blunts the effect of elevated sodium intake on blood pressure levels Sergio Lam^ego Rodrigues, MD, PhDa,*, Marcelo Perim Baldo, PhDa, Rebeca Caldeira Machado, MSca, Ludimila Forechi, MSca, Maria del Carmem Bisi Molina, PhDb, and Jose Geraldo Mill, MD, PhDa a
Department of Physiological Sciences, Federal University of Espırito Santo, 29042-755 Vit oria, Brazil; and b Department of Nutrition, Federal University of Espırito Santo, 29042-755 Vit oria, Brazil Manuscript received November 30, 2013 and accepted January 2, 2014
Abstract The purpose of this study was to investigate the influence of dietary potassium on the sodium effect on blood pressure (BP) in the general population and the adherence of current recommendations for sodium and potassium intake. An overnight (12-hour) urine sample was collected in a population-based study to investigate cardiovascular risk. A sub-sample of 1285 subjects (age range, 25–64 years) free from any medication interfering with BP or potassium excretion was studied. Of the participants, 86.0% consumed over 6 g of salt/day and 87.7% less than the recommended intake of potassium (4.7 g). Potassium excretion and the sodium to potassium ratio were significantly related to systolic and diastolic BP only in subjects consuming more than 6 g/day of salt. Subjects in the highest sodium to potassium ratio quartile (surrogate of unhealthy diet) presented 8 mm Hg and 7 mm Hg higher values of systolic and diastolic BP, respectively, when compared with the first quartile, while individuals in the fourth quartile of urinary potassium excretion (healthier diet) showed 6 mm Hg and 4 mm Hg lower systolic and diastolic BP, respectively, compared with the first quartile. Our data indicate that when people have an increased intake of potassium, high intake of sodium is not associated with higher BP. J Am Soc Hypertens 2014;8(4):232–238. Ó 2014 American Society of Hypertension. All rights reserved. Keywords: Blood pressure; potassium; sodium; hypertension.
Introduction Reduction of the intake of sodium has been established as a lifestyle change recommended to reduce cardiovascular diseases (CVD) mainly by decreasing blood pressure (BP) levels.1 Recently, the relationship between mortality and usual intake of sodium and potassium in American adults was reported. Higher intake of sodium was associated with increased overall mortality. Moreover, diets with
This study was supported with grants from CNPq (No. 302296/2008-5 and No. 561959/2010-2) and FINEP (No. 01 06 0300.00 ES). Disclosures: The authors declare no conflict of interest. *Corresponding author: Sergio Lam^ego Rodrigues, MD, PhD, Department of Physiological Sciences, Federal University of Espirito Santo, Av. Marechal Campos, 1468–29042-755, Vit oria, ES, Brazil. Tel.: þ55 27 33357335; fax: þ55 27 33357330. E-mail: [email protected]
higher sodium to potassium ratio (Na/K) were associated with increased risk of CVD and all-cause mortality.2 Diets with elevated content of sodium or increased Na/K ratio are related to increased BP and higher prevalence of hypertension.3,4 Hypertension is a major risk factor for several CVD including stroke, cardiac arrhythmias, heart failure, sudden cardiac death and chronic kidney disease.5 Therefore, it is not surprising that hypertension is present in around 69% of patients with the first myocardial infarction and around in 77% of patients with the first stroke.6 The association between the intake of sodium and hypertension is well established.2,3,7,8 However, the potential role of the intake of potassium to cardiovascular health has received less attention. It was reported that the intake of potassium estimated by food records was not independently associated with blood pressure.9 Conversely, two population-based studies showed that potassium intake— assessed by semi quantitative food frequency questionnaire10 or 24-hour recall dietary history11—was inversely
1933-1711/$ - see front matter Ó 2014 American Society of Hypertension. All rights reserved. http://dx.doi.org/10.1016/j.jash.2014.01.001
S.L. Rodrigues et al. / Journal of the American Society of Hypertension 8(4) (2014) 232–238
related to both diastolic BP (DBP) and systolic BP (SBP). Reports on interventional studies have also shown an inverse relation between potassium intake and BP. However, these studies were based on the use of potassium supplementation and/or controlled diets.12–17 It is worth mentioning that diet in interventional studies provides larger amounts of potassium, calcium, and magnesium than the typical diet, which can be a factor of confusion.18 Despite the elevated prevalence of hypertension associated with high salt consumption (around 12.8 g/day) in the Brazilian population,7 to date, there is scarce information regarding the influence of potassium intake on BP in the general population. Accordingly, a recent report on potassium intake and the estimated potential impact of increased potassium intake on population BP levels included 21 countries spread across North America, Europe, Asia, and Oceania, but South America in general and Brazil in particular.19 Therefore, the aim of this investigation was to estimate the influence of dietary potassium intake on the sodium effect on BP levels in the general population free from the influence of any medication interfering with blood pressure or potassium excretion and also to determine the adherence of the participants to the current recommendations for sodium and potassium intake.20
233
Anthropometric parameters were obtained by trained technicians. Body weight was taken on an electronic balance (Toledo, Brazil) and height in a wall-mounted stadiometer (Seca, Germany). Body mass index (BMI) was calculated as body weight (kg) to the squared height (m2). Waist circumference (WC) was measured at the mean point between the lowest rib margin and the iliac crest with the participant standing and at the maximum point of normal expiration. Smoking was considered present if the subject declared current use of tobacco cigarettes or pipe.
Sodium and Potassium Consumption
Data were collected to determine the prevalence and severity of cardiovascular risk factors in the urban population of Vitoria, Brazil. The design and sampling of this survey was described elsewhere.7,21 Briefly, a sample of 1661 individuals was selected by a procedure of household randomization. These individuals attended University Hospital to undergo clinical and laboratory exams to determine presence of cardiovascular risk factors. The project was approved by the Institutional Ethics Committee, and all participants gave informed written consent.
All participants received personal instructions at home about overnight urine collection. All urine produced during a 12-hour period (7:00 pm to 7:00 am) during the night preceding the clinic visit was collected in sterile plastic bottles. Participants were asked to record the time of the last void in the toilet before starting urine collection as well as the exact time of the last void in the bottle in the morning of clinic visit. At arriving on the clinic, the participants’ annotations were analyzed, and they were thoroughly questioned about the completeness. The validity of the urine as representative of a 12-hour period was accepted if the collect period ranged from 11 to 13 hours and if urine volume was 250 mL. From the original sample of 1661 subjects, 376 were excluded from the present analysis, because urine was not collected (n ¼ 10), urinary volume was 1.4 mg/dL (n ¼ 52), or there was use of antihypertensive drugs, including diuretics (n ¼ 270). Therefore, data are related to 1285 subjects (613 men and 672 women), free from the influence of any medication interfering with BP or potassium excretion. The daily sodium and potassium intake was estimated considering that 47% and 39%, respectively, of the 24hour total excretion on these substances in urine occurs during the night period (7:00 pm to 7:00 am)22 and that 77% of dietary potassium is excreted in urine.23 Salt consumption was estimated considering all sodium ingested as NaCl.22
Measurements
Statistical Analysis
Participants attended to the clinic at morning after 10 to 14 hours of fasting. BP was measured in the sitting position by using a standard mercury sphygmomanometer on the left arm after a 5 to 10 minute rest period. Mean values of SBP and DBP were calculated from two readings carried out by two independent trained staff members. Participants were considered hypertensive in presence of BP 140/ 90 mm Hg or when using antihypertensive drugs. A fasting venous blood sample was collected from each participant to determine glucose, creatinine, and lipids, by using validated commercial kits. Diabetes was defined in presence of fasting glucose >125 mg/dL or use of hypoglycemiants.
Statistical analysis was carried out using SPSS 18.0 (Chicago, IL, USA). Data were described as means standard deviation for continuous variables and proportions to categorical values. The goodness to fit to normal distribution was evaluated using the Kolmogorov–Smirnov test. Participants were divided by quartiles based on their 12-hour urinary potassium (urK) excretion and urinary sodium to potassium excretion ratio (urNa/K). Analysis of variance was used to compare means of continuous variables and the c2 test for categorical variables. Analysis of covariance was used to adjust for age, BMI, and urinary creatinine excretion (urCr). BMI, triglycerides, and urinary sodium
Methods Study Design and Sample Selection
234
S.L. Rodrigues et al. / Journal of the American Society of Hypertension 8(4) (2014) 232–238
Table 1 Baseline characteristics of the sample according to gender Variable
All Subjects (1285)
Age (years) SBP (mm Hg) DBP (mm Hg) BMI (kg/m2) Waist circumference (cm) Cholesterol (mg/dL) Triglycerides (mg/dL) HDL-c (mg/dL) Glucose (mg/dL) Creatinine (mg/dL) Salt intake (g/day) Potassium intake (g) Obesity (%) Arterial hypertension (%) Diabetes mellitus (%) Smoking (%)
43 124 82 25.7 85 212 134 45 102 0.97 12.9 2.9 15.5 31.0 5.3 25.2
Men (613)
10 (43) 192 (122) 13 (81) 5 (25) 12 (84) 47 (206) 133 (100) 13 (44) 27 (97) 0.2 (1.0) 7.4 (11.5) 1.8 (2.5)
44 128 86 25.6 88 213 160 42 104 1.0 14.0 3.2 13.8 41.1 6.2 29.1
P
Women (672)
11 (43) 18 (126) 13 (85) 4 (25) 11 (88) 51 (206) 169 (121) 12 (40) 27 (91) 0.2 (1.1) 7.0 (13) 1.9 (2.7)
43 120 79 25.8 81 211 109 49 100 0.87 12.0 2.7 17.0 21.7 4.5 22.3
10 (43) 20 (118) 12 (78) 5 (25) 12 (80) 43 (206) 81 (90) 12 (48) 26 (96) 0.2 (0.9) 6.0 (5) 1.8 (2.4)
.33
