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1Stomatology Division, Hebei General Hospital, Shijiazhuang, China
2Heart Center, Hebei General Hospital, Shijiazhuang, China
3The First Cardiology Division, The First Hospital of Hebei Medical University, Shijiazhuang, China
Submission: January 13, 2020; Published: February 07, 2020
*Corresponding author: Chao Liu, The First Cardiology Division, The First Hospital of Hebei Medical University, 89 Donggang Road, Shijiazhuang, Hebei Province, China, 050031
How to cite this article:Guan J, Zhai J, Zhao Q, Liu C. High Bioelectrical Impedance is Associated with High Blood Pressure Among US Adults - National Health
and Nutrition Examination Survey, 2001 And 2002. J Cardiol & Cardiovasc Ther. 2020; 15(5): 555923.
Background: Bioelectrical impedance analysis (BIA) is a simple method to estimate body composition. BIA measures the electrical impedance of body tissues that can be used to calculate an estimate of fluid volumes, total body water, body cell mass, and fat-free body mass. However, to our knowledge there are few studies that examine the relationship between BIA and blood pressure. Therefore, we designed the present study to test the relationship between blood pressure and BIA in US adults using data from the National Health and Nutrition Examination Survey (NHANES).
Methods: We reviewed data from 2328 subjects aged 18 years and older (maximum 49) who participated in the NHANES between 2001 and 2002. Blood pressure was indexed to the body mass index (BMI) to standardize the impact of fat tissue. The Pearson correlation coefficients were derived. We also conducted partial correlation using age and gender as co-variables to rule out the potential bias. A multiple linear regression was used to model the dependence of blood pressure on age, gender, and BIA.
Results: There was a significantly correlation between BIA (i.e. fluid volume) and systolic blood pressure (r = 0.35 to 0.39, P < 0.001) and diastolic blood pressure (r = 0.36 to 0.39, P < 0.001). All these correlations were further strengthened after adjusting for age and gender.
Conclusion: BIA (i.e. fluid volume) positively correlated to blood pressure in US adults; however, because this was an observational study, further investigation is needed to verify our results as well as identify the mechanisms.
Keywords: Bioelectrical impedance analysis; Body mass index; Systolic blood pressure; Diastolic blood pressure; Association; Adults
Abbrevations: BIA: Bioelectrical Impedance Analysis; BMI: Body Mass Index; BI: Bioelectrical Impedance; BP: Blood Pressure; MSNA: Muscle Sympathetic Nerve Activity; BCM: Body Cell Mass
In human tissue, bioelectrical impedance is high in fat tissue and low in lean tissue. Nonfat or lean tissue is highly conductive due to its richness in intracellular fluid and electrolytes. Whereas, fat tissue contains very little fluid, thus has high resistance to electrical current. Bioelectrical impedance analysis (BIA) is a simple method to estimate body composition. BIA measures the electrical impedance of body tissues that can be used to calculate an estimate of fluid volumes, total body water, body cell mass, and fat-free body mass.
Hypertension is the most common chronic condition and one of leading causes of morbidity and mortality in the world. The causes of primary hypertension are complex and not fully understood. Nevertheless, the links between environmental factors, such as excess intake of salt, obesity, and perhaps sedentary lifestyle, and hypertension have been well established in studies over the past several decades. The efficacy of the diuretic therapy to alter fluid volumes and lower blood pressure has been proven in the patients with hypertension. Additionally, age also play an important role in the progress of hypertension because the aorta is stiffening with increasing age. It is worthy of noting that the above factors, such
as obesity, body fluid volume, and age can affect the bioelectrical
impedance (BI) as well. However, to our knowledge there are
few studies that examine the relationship between BI and blood
pressure (BP). Therefore, we designed the present study to test
the relationship between BP and BI in US adults using data from
the National Health and Nutrition Examination Survey (NHANES).
This cross-sectional study used data from 2328 subjects aged
18 and older (maximum 49) who participated in the NHANES
between 2001 and 2002 . The survey provides information
on the demographics and health status of the US civilian, noninstitutionalized
population by using a complex, stratified,
multistage, probability-sampling design . Demographic
characteristics can be found in Table 1.
Data are expressed as mean ± standard deviation. BMI, body mass
The average systolic and diastolic pressures were used to
analyze the relationships between BP and BI. The average BPs
were calculated using the following protocol: If more than one BP
readings were obtained, the first BP reading was excluded from
the average. If there was only one BP reading, that reading was
the average. If there were only two BP readings, the second BP
reading was the average. If all diastolic BP were 0, the average
was 0. Exception: if one of diastolic BP reading was 0, the diastolic
BP reading with 0 was not used to calculate the average. If 2 of 3
diastolic BP reading are 0, then the reading that is not 0 was used
to calculate the average .
The protocol of BIA was described elsewhere . In brief,
the examinees were in a supine position. The arms should be
separated from 15 degrees from the trunk of the body and the
legs comfortably separated. Multi-frequency BIA, using different
frequencies, was passed between surface electrodes placed on
right hand and right foot. At frequencies below 5 kHz, and above
200 kHz, poor reproducibility has been noted. Therefore, we used
5, 50, 100, and 200 kHz to evaluated bioelectrical impedance.
Statistical analyses were carried out using SPSS 16.0 statistical
package. Blood pressure was indexed to the Body Mass Index (BMI)
to standardize the impact of fat tissue. The Pearson correlation
coefficients were derived. We also conducted partial correlation
using age and gender as co-variables to rule out the potential bias.
A multiple linear regression was used to model the dependence of
blood pressure on age, gender, and BI. Standardized coefficients
were calculated to reflect the relationship between BP and the
above variables. All statistical tests were two-sided and P-value <
0.05 was considered as significant.
The analysis using Pearson’s correlation coefficient between
BI and systolic BP are shown in Figure 1. There was a strong
correlation between BI and systolic BP (Figure 1A-D). The
correlations were consistent at variable frequency BIA, (5 kHz,
50 kHz, 100 kHz and 200 kHz). The correlation between BI
and systolic BP remained unchanged in partial correlation in
which age and gender were taken as co-variables (Table 2). In
multiple linear regression models, standardized coefficients were
calculated. Finally, the relationship between BI and systolic BP
was established, which was consistent with unadjusted results.
As showed in Figure 1 (Figure 1E-H), there was a strong
correlation between BI and systolic BP using Pearson’s correlation
coefficient. The correlations were consistent at variable frequency
BIA, (5 kHz, 50 kHz, 100 kHz and 200 kHz). The correlation
between BI and diastolic BP remained unchanged in partial
correlation in which age and gender were taken as co-variables
(Table 3). Similar to the above multiple linear regression model,
the relationship between BI and diastolic BP was established as
well (Table 3).
Our study showed that there is a moderate but statistically
significant positive correlation between BP and BI that is
independent of age, BMI, and gender, indicating fluid volume
overload contributes to the BP in adults.
A positive association of overweight and hypertension has
been consistently reported from numerous cross-sectional and
prospective studies over many decades. Over the past decades, a link between obesity and hypertension development has also
been well established [4,5]. More specifically, visceral adipose,
rather than total adiposity, play a more important role in this
relationship . It is well also well documented there is a positive
association between overweight and high BI as well. However,
the correlation between BP and BI remains unchanged after
standardizing BP with BMI (i.e. the body fat mass) in the present
study, indicating there must be some other mechanisms needing
to be clarified.
Gender has an important impact on blood pressure.
Premenopausal women tend to have lower arterial blood pressure
and less risk of hypertension than age-matched men. Sex hormones
such as estradiol and testosterone have direct impact on vascular,
renal and heart cells. Overall, evidence showed that estradiol is
anti-hypertensive, whereas testosterone is hypertensive .
Sex hormones also have direct role impact on body fat mass. To
eliminate the impact of gender, we controlled the gender at partial
correlation analysis. However, the association between BIA and
systolic pressure still exist after controlling the impact of gender.
As people age, blood pressure tends to increase, so does
the risk of hypertension [7,8]. The mechanisms of age-related
arterial blood pressure elevation are complex. Several underlying
mechanisms have been proposed . First, muscle sympathetic
nerve activity (MSNA) increases with age , which can
contribute to the increase in BP. Second, inflammation increases
with age. Increased inflammation response leads to infiltrations
of T cells and macrophages that could cause tissue injury and
arterial stiffening. Third, the prevalence of metabolic syndrome
also increased with age. In such subjects, vascular endothelial
dysfunction and oxidative stress activates extracellular matrix
metalloproteinases, resulting in vascular remodeling and arterial
stiffening. To eliminate the impact of age, we controlled the age at
partial correlation analysis. However, the association between BIA
and systolic pressure still exist after controlling the impact of age.
The strengths of this study include the nationwide populationbased
samples from national health surveys with largely identical
sampling and measurement methods, the standardization of BP,
weight and height measurements and the availability of highquality
BIA data. It is a limitation of our analysis that we could not
adjust for the intake of salt, fruit and vegetables that are related
to both BMI and BP. These parameters were either not measured
There are several limitations to the study. First, this is a crosssectional
observational study. Thus, we are unable to draw a
causal relationship between BI and hypertension. Second, we did
not have available measures of site-specific adiposity, so we were
unable to assess the relationship between adipose distributions
and BP. The trunk of the body with its large cross- sectional area
contributes as little as 10% to whole body impedance whereas it
represents as much as 50% of whole-body mass . Therefore,
changes of the impedance are closely related to changes muscle
mass or body cell mass (BCM) of the limbs，instead of the trunk.
Even large changes in the visceral adipose within the abdominal
cavity may have only minor influence on the measurement of fatfree
mass or BCM . Segmental-BIA may be helpful in providing
information on fat accumulation in the abdominal region of the
Bioelectrical impedance, i.e. fluid volume, positively correlates
to blood pressure in US adults; however, because this was an
observational study, further investigation is needed to verify our
results as well as identify the mechanisms.
Centers for Disease Control and Prevention, National Center for Health Statistics National Health and Nutrition Examination Survey Data US Department of Health and Human Services, Centers for Disease Control and Prevention, Hyattsville, MD (1999-2000).