The aim of this study was to investigate whether intake of dietary sodium or potassium is related to changes in left ventricular (LV) diastolic functioning and LV mass index in young subjects with normal or elevated blood pressure. We prospectively analyzed echocardiographic data in 1,065 young adults (18 to 39 years) enrolled in the Strong Heart Family Study who were free from cardiovascular disease at baseline: 501 (47%) participants were normotensive and 564 (53%) were prehypertensive or hypertensive. Dietary sodium and potassium intakes were ascertained using a block food frequency questionnaire at baseline. Cardiac geometry and functioning were assessed at baseline and 4 years later. Marginal models were used to assess the associations of average intakes of sodium and potassium with echocardiographic measures. Participants with prehypertension or hypertension were older, had higher body mass index, and reported higher intakes of sodium than normotensive subjects at baseline. In prospective analyses, potassium intake was found to be negatively related to mitral E velocity (p = 0.029) in normotensive subjects, whereas sodium/potassium ratio was positively associated with atrial filling fraction (p = 0.017). In prehypertensive or hypertensive participants, sodium consumption was positively associated with atrial filling fraction (p = 0.034) and an increase in sodium/potassium ratio was related to higher LV mass index (p = 0.046). In conclusion, an increase in dietary sodium/potassium ratio was related to an accentuation of atrial phase LV diastolic filling in normotensive young subjects, whereas in prehypertensive or hypertensive subjects it was associated with higher LV mass index.
Sodium restriction and potassium supplementation are recommended dietary measures to prevent cardiovascular disease. Previous studies have linked dietary sodium intake with changes in cardiac structure, notably increased left ventricular (LV) mass. Already before cardiac remodeling, measures of cardiac functioning deteriorate. In otherwise healthy patients at high risk or at an early stage for hypertensive disease, subtle changes in cardiac diastolic functioning can be detected by echocardiography as a consequence of dietary sodium loading that may indicate an early stage of LV remodeling. To this point, surprisingly little is known about the relation between dietary sodium and potassium intakes and LV structure and function in young subjects in large population-based samples as comprehensive prospective analyses are largely missing. Early identification of echocardiographic alterations in LV function in young populations could help to screen for those subjects at high risk for LV structural changes. The aim of this study was to investigate whether dietary sodium or potassium intake is related to changes in LV diastolic function and LV mass in young subjects with normal or elevated blood pressure (BP).
Methods
The Strong Heart Study (SHS) is a longitudinal population-based survey of cardiovascular risk factors and disease in American Indians from 13 communities in Arizona, Oklahoma, and South and North Dakota that was initiated in 1988. The SHS design and methods have been described previously. In brief, the Strong Heart Family Study (SHFS) was conducted between 2001 and 2003 (SHS examination IV) with a follow-up visit in 2007 to 2009 (SHS examination V). It enrolled 1,468 men and 2,197 women from 96 large families of SHS participants. All participants of the SHFS received extensive examinations including a transthoracic echocardiogram at both visits. For this analysis, we included only SHFS participants aged 14 to 39 years. Participants with a history of any cardiovascular disease (i.e., myocardial infarction, angina pectoris, heart failure, coronary bypass surgery, angioplasty, carotid endarterectomy, valve replacement and significant valve disease [aortic or mitral stenosis or more than mild regurgitation], or history of stroke at SHS examination IV) were excluded. Subjects with missing or incomplete dietary information or with extreme calorie intake (i.e., <500 or >3,500 kcal/d) were also excluded from this analysis. Our final study population consisted of 1,065 study participants. Participants were followed up for an average of 4 years. The institutional review boards (Cornell University, MedStar Health, and University of Oklahoma), Indian Health Service IRB (Phoenix, Oklahoma, and Aberdeen), and each participating tribe approved the study. Written informed consent was obtained from all participants at enrollment.
BP status was assessed by the average of 2 BP readings at baseline examination. Prehypertension was defined as systolic BP between 120 and 139 mm Hg and diastolic BP between 80 and 89 mm Hg with no hypertension treatment. Hypertension was defined as systolic BP ≥140 or diastolic BP ≥90 or taking hypertension medication. Diabetes was diagnosed if fasting plasma glucose was ≥126 mg/dl or if the participant was on diabetes medications. Body mass index was calculated as body weight divided by height squared (kg/m 2 ).
An interviewer-administered block 119-item food frequency questionnaire was applied to all participants at baseline. To compute measures of average daily sodium and potassium intakes, the frequency response for each food on the FFQ was multiplied by the nutrient content of the documented portion size of the food and then summed for all foods.
Echocardiographic measures of cardiac geometry and function were collected in all participants by expert sonographers and reviewed offline by a highly experienced investigator. Cardiac geometry was assessed by the following parameters: LV internal diameter was measured at end-diastole and adjusted for height, whereas left atrial diameter was measured in end-systole. LV mass was calculated by a necropsy-validated formula and was normalized to height in meters 2.7 (LV mass index). Left ventricular systolic function was assessed by calculating ejection fraction as the ratio of stroke volume/end-diastolic volume. Stroke volume was calculated as the difference between end diastolic and end systolic volumes by the z-derived method and was normalized to height 2.04 . LV diastolic function was evaluated by Doppler interrogation. Transmitral early (E) and late (A) LV filling velocity were measured at the annular level and used to compute the early peak rapid filling velocity to peak atrial filling velocity ratio (E/A ratio). Similarly, deceleration time (DT) of early diastolic LV filling and the atrial filling fraction were calculated. Isovolumic relaxation time (IVRT), a raw index of active LV relaxation, was measured between aortic valve closure and mitral valve opening.
The baseline characteristics and echocardiographic measures by hypertension status at baseline (SHS examination IV) were compared using t test and/or logistic or marginal models. Marginal models were also used to assess the association of average intakes of sodium and potassium and also sodium/potassium ratio in SHS examination IV with echocardiographic measures in SHS examination V separately for normotensive and prehypertension/hypertension groups. Models were adjusted for age, gender, field center, relatedness among family members, and the respective baseline echocardiographic measures. Similar to previous analyses from the SHFS, the impact of relatedness among family members was considered using standard kinship coefficients (i.e., 0.25 for parent/offspring, 0.25 for full siblings, 0.125 for half-siblings, and 0 for no consanguinity). All p-values were 2 tailed. A p-value <0.05 was considered significant. Data were analyzed with SAS 9.3 (SAS Corp., Cary, North Carolina).
Results
Characteristics of study participants by BP status at baseline (SHS examination IV) are presented in Table 1 . Participants with prehypertension/hypertension were significantly older, predominantly female, more likely to be diabetic, had higher body mass index, and consumed higher amounts of sodium. Echocardiographic measures of prehypertensive/hypertensive and normotensive subjects at baseline and the follow-up examinations are presented in Table 2 . Left atrium diameter, LV diameter, and LV mass index were significantly higher in prehypertensives/hypertensives. Among parameters of cardiac functioning, prehypertensives/hypertensives had a significantly higher heart rate and stroke work but lower systolic output reflected by lower ejection fraction. In diastole, mitral E velocity was similar, whereas mitral A velocity was significantly higher resulting in a lower E to A ratio in prehypertensives/hypertensives. Last, DT and IVRT were significantly longer, and atrial filling fraction was higher in prehypertensives/hypertensives. All changes of those cardiac geometry and functioning measures between the follow-up and baseline examinations in Table 2 were significant except heart rate and DT in both prehypertensives/hypertensives and normotensives, A-velocity in normotensives and stroke work in prehypertensives/hypertensives. Associations of changes in cardiac geometry are presented in Table 3 and Table 4 . In normotensive participants ( Table 3 ), sodium or potassium intake was not associated with changes in left atrium diameter, LV diameter, or LV mass. Among parameters of cardiac diastolic functioning, potassium intake at baseline was found to be negatively related to change in mitral E-velocity (p = 0.0294, p = 0.0231 after further adjustment for baseline diabetes status), whereas sodium/potassium ratio was positively associated with change in the atrial filling fraction (p = 0.0171, p = 0.018 after further adjustment for baseline diabetes status). Sodium or potassium intake did not alter LV systolic functioning or other LV diastolic parameters such as DT, IVRT, or E to A ratio. In prehypertensives/hypertensives ( Table 4 ), sodium/potassium ratio was found to be positively associated with LV mass index (p = 0.0459, p = 0.0486 after further adjustment for baseline diabetes status). Atrial filling fraction was observed to be positively related to sodium consumption (p = 0.0338, p = 0.0335 after further adjustment for baseline diabetes status), whereas other cardiac functioning parameters were not associated with either sodium or potassium intake.
| Variable | Pre-HTN or HTN (n=564) | Normal Blood Pressure (n=501) | p -value † | ||
|---|---|---|---|---|---|
| Mean | STD | Mean | STD | ||
| Age (years) | 29.29 | 6.51 | 27.4 | 6.79 | <0.0001 |
| Women (%) | 53.19 | 21.96 | <0.0001 | ||
| Systolic Blood Pressure (mmHg) ∗ | 126 | 11 | 108 | 7 | <0.0001 |
| Diastolic Blood Pressure (mmHg) ∗ | 82 | 9 | 69 | 7 | <0.0001 |
| Diabetes Mellitus (FPG) (%) | 16.37 | 5.41 | <0.0001 | ||
| Body Mass Index (kg/m 2 ) | 34.58 | 8.12 | 30.87 | 8.27 | <0.0001 |
| Sodium Intake (mg/d) | 2717 | 1158 | 2554 | 1099 | 0.0192 |
| Potassium Intake (mg/d) | 2500 | 1043 | 2442 | 1070 | 0.3675 |
| Sodium / Potassium Ratio | 1.11 | 0.27 | 1.09 | 0.31 | 0.3140 |
| Total Energy Intake (kcal/d) | 2088 | 765 | 2003 | 749 | 0.0686 |
| Field Center | |||||
| Arizona (%) | 38.48 | 32.73 | |||
| Oklahoma (%) | 34.40 | 29.34 | |||
| South Dakota (%) | 27.13 | 37.92 | |||
∗ From those without hypertension medications.
† p-value from testing difference of means/rates between Pre-HTN/HTN and Normal Blood Pressure groups.
| Variable | Baseline exam (Examination IV) | Follow-up exam (Examination V) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Pre-HTN or HTN | Normal Blood Pressure | Pre-HTN or HTN | Normal Blood Pressure | ||||||||
| Mean | STD | Mean | STD | p ∗ | Mean | STD | p † | Mean | STD | p † | |
| Cardiac Geometry | |||||||||||
| Left atrium diameter (cm) | 3.74 | 0.44 | 3.48 | 0.43 | <0.0001 | 3.85 | 0.47 | <0.0001 | 3.61 | 0.48 | <0.0001 |
| Left ventricular diameter (cm) at diastole/height(m) | 3.17 | 0.23 | 3.12 | 0.21 | 0.0047 | 3.27 | 0.25 | <0.0001 | 3.21 | 0.24 | <0.0001 |
| Left ventricular mass index | 78.60 | 14.23 | 71.54 | 13.46 | <0.0001 | 79.67 | 15.84 | 0.0345 | 69.97 | 12.81 | 0.0007 |
| Cardiac Functioning | |||||||||||
| Heart Rate (beats/min) | 69 | 12 | 65 | 10 | <0.0001 | 69 | 12 | 0.5264 | 65 | 15 | 0.9677 |
| EF (%) | 59.65 | 4.96 | 60.59 | 4.94 | 0.0008 | 58.06 | 4.68 | <0.0001 | 59.19 | 4.13 | <0.0001 |
| Stroke work (ml) | 149.34 | 34.32 | 122.18 | 24.20 | <0.0001 | 150.11 | 38.90 | 0.4984 | 126.72 | 30.65 | 0.0017 |
| E-velocity (cm/s) | 89.53 | 17.02 | 90.46 | 15.14 | 0.2116 | 83.32 | 17.36 | <0.0001 | 83.20 | 14.98 | <0.0001 |
| A-velocity (cm/s) | 59.36 | 15.39 | 54.81 | 13.43 | <0.0001 | 61.42 | 16.31 | 0.0072 | 56.23 | 13.45 | 0.1437 |
| E to A ratio | 1.59 | 0.44 | 1.74 | 0.50 | <0.0001 | 1.42 | 0.39 | <0.0001 | 1.54 | 0.39 | <0.0001 |
| Deceleration time (ms) | 172.43 | 36.11 | 166.07 | 37.15 | 0.0082 | 173.73 | 43.14 | 0.6330 | 165.60 | 41.09 | 0.8530 |
| IVRT (ms) | 78.80 | 10.44 | 76.01 | 10.53 | 0.0005 | 74.65 | 10.88 | <0.0001 | 73.92 | 10.45 | 0.0006 |
| Atrial filling fraction | 0.27 | 0.08 | 0.24 | 0.07 | <0.0001 | 0.35 | 0.34 | <0.0001 | 0.33 | 0.29 | <0.0001 |
∗ p-value from testing difference of means between Pre-HTN/HTN and Normal Blood Pressure groups.
† p-value from testing measure difference between follow-up and baseline exams.
| Variable | Sodium | Potassium | Sodium/Potassium Ratio | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Estimated Coeff. | StdErr | P | Estimated Coeff. | StdErr | P | Estimated Coeff. | StdErr | P | |
| Cardiac Geometry | |||||||||
| Left atrium diameter (cm) | -0.000015 | 0.000012 | 0.1996 | -0.000022 | 0.000012 | 0.0693 | 0.0215 | 0.0421 | 0.6104 |
| Left ventricular diameter (cm) at diastole/height(m) | -0.000006 | 0.000007 | 0.3484 | -0.000002 | 0.000007 | 0.7535 | -0.0197 | 0.0242 | 0.4156 |
| Left ventricular mass index | -0.000103 | 0.000376 | 0.7835 | 0.000189 | 0.000379 | 0.6178 | -1.8375 | 1.3430 | 0.1720 |
| Cardiac Functioning | |||||||||
| Heart Rate (beats/min) | -0.000225 | 0.000660 | 0.7332 | -0.000035 | 0.000670 | 0.9587 | -0.6536 | 2.3437 | 0.7805 |
| Ejection Fraction (%) | -0.000072 | 0.000152 | 0.6348 | -0.000180 | 0.000155 | 0.2462 | 0.6311 | 0.5451 | 0.2476 |
| Stroke work (ml) | -0.000702 | 0.001186 | 0.5543 | -0.000833 | 0.001207 | 0.4904 | -2.0224 | 4.3474 | 0.6420 |
| E-velocity (cm/s) | -0.000687 | 0.000619 | 0.2677 | -0.001363 | 0.000624 | 0.0294 | 2.4487 | 2.2276 | 0.2723 |
| A-velocity (cm/s) | 0.000259 | 0.000526 | 0.6226 | 0.000148 | 0.000532 | 0.7815 | 0.1488 | 1.9013 | 0.9376 |
| E to A ratio | -0.000018 | 0.000016 | 0.2513 | -0.000026 | 0.000016 | 0.1055 | 0.0141 | 0.0571 | 0.8054 |
| Deceleration time (ms) | -0.000715 | 0.001839 | 0.6977 | -0.000443 | 0.001863 | 0.8119 | -5.5109 | 6.6320 | 0.4065 |
| Isovolumic relaxation time (ms) | 0.000126 | 0.000467 | 0.7877 | -0.000221 | 0.000475 | 0.6425 | 1.3776 | 1.6658 | 0.4087 |
| Atrial filling fraction | 0.000006 | 0.000013 | 0.6216 | -0.000010 | 0.000013 | 0.4408 | 0.1147 | 0.0479 | 0.0171 |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
