13 / 67
CARDIOVASCULAR JOURNAL OF AFRICA • Volume 26, No 2, March/April 2015
AFRICA
59
Urinary sodium and potassium concentrations in the aliquots
were measured using the ion-selective electrode method on a
Medica Easylyte Plus Na/K/Cl analyser (Netherlands). Sodium
(Na) was converted from millimoles (mmol) to grams by dividing
by 17 and the conversion from sodium to salt (sodium chloride)
was made by multiplying by 2.542, as previously proposed.
26
Anthropometric and blood pressure measurement
Weight and height were measured using a digital electronic
balance equipped with a digital stadiometer (SECA, GmbH &
Co, Germany; range 0.1–250 kg, precision 50 g and range 110–200
cm, precision 0.1 cm, respectively). Body mass index (BMI) was
calculated as the weight divided by the square of the height (kg/
m
2
). According to BMI values, individuals were classified as
overweight (25.0–29.9 kg/m
2
) and obese (
≥
30.0 kg/m
2
).
27
The waist and hip circumferences were measured with
participants in a standing position using a non-extending
1-cm-wide measuring tape. The waist circumference was
measured at the end of normal expiration, at the midpoint
between the lower border of the rib cage and the top of the iliac
crest, and recorded to the nearest 0.1 cm.
Blood pressure and heart rate were measured in triplicate
after five minutes of resting in a seated position, using a
validated, automated digital oscillometric sphygmomanometer
(Omron 705CP, Tokyo, Japan). The readings were repeated at
three-minute intervals. The mean of the last two readings was
recorded. Hypertension was defined as systolic blood pressure
≥
140 mmHg, and/or diastolic blood pressure
≥
90 mmHg, and/or
the use of antihypertensive drugs.
A standard 12-lead electrocardiogram (ECG) recorded at
rest for each participant, using a computerised device (Schiller
AT-10 EKG, Baar, Switzerland). Each ECG was assessed by
an experienced observer who was blinded to other clinical
characteristics of the participants.
Statistical analysis
The normality of the data was checked using the Kolmogorov–
Smirnov test. Continuous variables are reported as mean
±
standard deviation or median and interquartile range (25th – 75th
percentile). These variables were compared by gender using the
independent samples
t-
test or Mann–Whitney test for normally
or non-normally distributed data, respectively. Categorical
variables were expressed as proportions and compared using the
chi-square test or Fisher’s exact test if appropriate. Data were
analysed using SPSS software, version 13.0 (SPSS Inc, Chicago,
IL). A two-tailed
p
<
0.05 was considered statistically significant.
Results
The response rate for the random sample was approximately 68%
(123/181) of the planned study sample after excluding subjects
with potentially confounding factors that could influence urinary
excretion of sodium and potassium. Of the 123 participants, the
mean age was 22.6
±
4.3 years (range 17–43), and more were
women (56.1%) with a similar age to the men. The characteristics
of the population are presented in Table 1.
When compared with women, men had significantly higher
mean values for weight, height and systolic blood pressure, and
higher levels of blood creatinine and uric acid. Women had
significantly higher heart rate values compared to men. The
proportion of subjects with obesity and a sedentary lifestyle was
significantly higher in women than men. There was no significant
difference between men and women regarding the prevalence of
hypertension, diabetes, obesity and alcohol consumption. None
of the participants reported current or past smoking.
Participant’s answers to the questionnaire regarding their
knowledge, attitude and behaviour on dietary salt are shown in
Table 2. The majority of participants stated that salt was always
added in preparing food at home, and rarely or sometimes
added to food at the table. It was also observed that almost
all participants knew that a high-salt diet could cause health
problems, and 91.1% of them recognised the importance
of reduced salt in the diet. However, less than half of the
participants (45.5%) were aware of their high dietary sodium
intake, and most reported a preventative measure was the
avoidance of adding salt at the table.
Less-reported measures were: avoidance or minimising salt
intake, use of low-sodium or low-salt alternatives, avoidance of
adding salt when cooking, and avoiding eating out. Unexpectedly,
none of the participants reported the habit of reading food labels
to see the sodium content before consumption. Similarly, our
participants were unaware of the possibility of using spices with
lower sodium content as a salt substitute in cooking.
When participants were asked their perception of the amount
of salt they were consuming, the majority of them classified their
own level of salt consumption as ‘just right’ or ‘too little’. Only
6.5% of participants recognised they consumed salt excessively.
Table 1. Characteristics of the participants by gender
Characteristics
All
(
n
=
123)
Men
(
n
=
54)
Women
(
n
=
69)
p
-value
Number (%)
123 (100)
54 (43.9)
69 (56.1)
0.245
Age (years)
22.6
±
4.3
22.9
±
4.4
22.5
±
4.3
0.595
Weight (kg)
60.6
±
13.1
64.5
±
13.6 57.6
±
11.8 0.003
Height (cm)
165.6
±
7.8
170.3
±
7.4 162.0
±
6.1
<
0.001
WC (cm)
72.4
±
9.9
74.1
±
10.6 71.0
±
9.2
0.088
HC (cm)
91.7
±
10.4
90.2
±
10.4 92.9
±
10.4 0.150
BMI (kg/m
2
)
22.0
±
3.9
22.1
±
3.5
21.9
±
4.2
0.819
SBP (mmHg)
113.8
±
11.4 119.9
±
11.6 109.6
±
9.4
<
0.001
DBP (mmHg)
68.1
±
7.5
67.6
±
7.4
68.5
±
7.6
0.501
Heart rate (bpm)
75.0
±
11.0
72.0
±
11.0 78.0
±
9.0
0.002
Glucose (mg/dl)
90.3
±
11.1
89.1
±
12.4 91.2
±
9.9
0.306
(mmol/l)
(5.01
±
0.62)
(4.95
±
0.69)
(5.06
±
0.55)
Creatinine (mg/dl)
0.96
±
0.13
1.07
±
0.10 0.88
±
0.09
<
0.001
(μmol/l)
(84.86
±
11.49) (94.59
±
8.84) (77.79
±
7.96)
Uric acid (mg/dl)
4.8
±
1.2
5.5
±
1.0
4.2
±
1.0
<
0.001
TC (mg/dl)
171.7
±
36.4 175.5
±
39.7 168.8
±
33.6 0.311
(mmol/l)
(4.45
±
0.94)
(4.55
±
1.03)
(4.37
±
0.87)
TG (mg/dl)
79.3
±
36.7
79.2
±
36.3 79.5
±
37.4 0.962
(mmol/l)
(0.9
±
0.41)
(0.89
±
0.41)
(0.9
±
0.42)
Hypertension,
n
(%)
4 (3.3)
3 (5.6)
1 (1.4)
0.203
Diabetes,
n
(%)
1 (0.8)
1 (1.9)
0 (0.0)
0.256
Overweight,
n
(%)
17 (13.8)
8 (14.8)
9 (13.0)
0.551
Obesity,
n
(%)
4 (3.3)
1 (1.9)
3 (4.3)
0.001
Sedentary,
n
(%)
97 (78.9)
35 (64.8)
62 (89.9)
0.001
Alcohol intake,
n
(%)
19 (15.4)
12 (22.2)
7 (10.1)
0.132
Values are means
±
standard deviation or percentages. WC, waist circumference;
HC, hip circumference; BMI, body mass index; SBP, systolic blood pressure;
DBP, diastolic blood pressure; TC, total cholesterol; TG, triglycerides.