CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 5, September/October 2011
AFRICA
253
Table 5 compares the mean (geometric) iron indices among
four BMI categories. In men, mean (geometric) serum TIBC
was significantly higher in the normal-weight group compared to
the underweight group before (
p
=
0.016) and after (
p
=
0.018)
adjusting for age and smoking. Additionally, mean (geometric)
serum TIBC was significantly higher in the overweight than the
underweight (
p
=
0.047) groups after controlling for age and
smoking. No significant differences were observed in ferritin,
serum iron and haemoglobin concentrations and percentage
transferrin saturation among men in the different BMI categories
before and after adjusting for age and smoking.
For women, mean (geometric) serum ferritin concentration
was significantly higher in the underweight group than the
normal-weight, overweight and obese groups before (
p
=
0.001,
p
=
0.020,
p
=
0.014, respectively) and after (
p
=
0.017,
p
=
0.037,
p
=
0.007, respectively) controlling for age and smoking.
A significantly higher mean (geometric) haemoglobin concen-
tration was observed in the underweight compared to the over-
weight (
p
=
0.036) and obese (
p
=
0.013) groups, although only
the difference between the underweight and obese was retained
(
p
=
0.022) after adjusting for age and smoking.
Percentage transferrin saturation was higher in the overweight
than obese women before (
p
=
0.014) and after (
p
=
0.016)
adjusting for age and smoking. Obese women had a lower mean
(geometric) serum iron than the normal-weight (
p
=
0.047) and
overweight (
p
=
0.006) women but only the difference between
the overweight and obese remained significant (
p
=
0.013) after
adjusting for age and smoking. No significant differences in
TIBC were observed for the different BMI categories before and
after adjusting for age and smoking.
Discussion
This is the first study to our knowledge that assessed the rela-
tionship between iron indices and anthropometric CVD markers
in an African population. This study employed anthropometric
measures, which have been reported to be associated with CVD
risk. These factors include WC, WHR, triceps and subscapular
skinfold thicknesses (TSF and SSF), percentage body fat and
BMI.
15,24
The results showed that both men and women in the
high-WHR category had higher ferritin concentrations than those
in the normal-WHR category. A positive association between
ferritin concentrations and BMI, WC, WHR, percentage body fat
and SSF was demonstrated for both men and women; although
this disappeared after adjusting for age, BMI and smoking. WC
and WHR increased with increasing ferritin concentrations in
both men and women. Serum iron concentrations decreased with
increasing BMI in women only.
The results obtained in this study are similar to the work of
Gillum
25
who reported that serum ferritin concentrations associ-
ated positively with WHR and BMI in Mexican-American men.
Norwegian men aged 20–49 years were also reported to have
a mean serum ferritin concentration that related positively to
their mean BMI.
26
Additionally, a study conducted on diabetic
patients reported that serum ferritin concentrations correlated
positively with visceral fat and subcutaneous fat area. This study
excluded patients with high C-reactive protein concentrations in
order to exclude elevation of ferritin that may have been caused
by inflammation. The authors therefore concluded that ferritin
concentrations might be a useful indicator of systemic percent-
age fat.
27
Conversely, Eftekhari
et al
.
28
reported a negative correlation
between serum ferritin concentrations and BMI in adolescent
Iranian girls. This is in contrast to the results of this study that
showed a positive correlation between serum ferritin concentra-
tions and BMI. The authors attributed the result to the age group
of the study population. Adolescence, being a peculiar stage of
growth, is characterised by a growth spurt and increased iron
requirements. The onset of menstruation in girls makes their
TABLE 5. COMPARISON OF IRON INDICESACCORDINGTO BMI CATEGORIES
Underweight
(BMI
<
18.50 kg/m
2
)
Normal weight
(BMI 18.50–24.90 kg/m
2
)
Overweight
(BMI 25.00–29.90 kg/m
2
)
Obese
(BMI
3
≥
30.00 kg/m
2
)
Variable
G-Mean (SE)
Min, max G-Mean (SE)
Min, max G-Mean (SE)
Min, max G-Mean (SE)
Min, max
Men
(
n
=
165, 23.21%)
(
n
=
451, 63.43%)
(
n
=
69, 9.70%)
(
n
=
26, 3.66%)
Serum Fe (
µ
mol/l)
16.05 (0.77) 0.74, 73.42 16.75 (0.40)
1.02, 63.94 16.46 (0.91)
3.25, 38.04 15.67 (1.40)
3.62, 36.57
Serum TIBC (
µ
mol/l)
61.62 (0.94) 28.77, 97.77 64.49*
#
(0.65) 36.54, 197.22 64.84
$
(1.55) 41.64, 109.50 64.89 (15.67) 46.26, 84.48
Transferrin saturation (%) 26.05 (1.28) 2.20, 97.36 25.97 (0.65) 1.34, 102.22 25.38 (1.37)
5.02, 63.14 24.15 (2.12)
4.57, 54.91
Serum ferritin (
µ
g/l)
92.26 (20.90) 2.50, 2387.60 101.59 (16.95) 1.00, 2877.17 134.52 (16.81) 1.54, 807.22 174.02 (46.58) 5.86, 956.88
Hb (g/dl)
13.43 (0.18) 7.40, 22.90 13.22 (0.09)
4.70, 21.10 13.25 (0.21)
8.90, 17.70 13.90 (0.47) 11.00, 21.10
Women
(
n
=
56, 5.90%)
(
n
=
380, 40.049%)
(
n
=
242, 25.50%)
(
n
=
271, 28.56%)
Serum Fe (
µ
mol/l)
11.75 (1.36) 1.85, 51.55 13.12 (0.39)
1.18, 40.96 14.33 (0.46)
2.30, 56.30 12.42
µ
♀
σ
(0.42) 0.26, 59.85
Serum TIBC (
µ
mol/l)
68.95 (2.83) 29.13, 171.12 68.49 (0.69) 32.97, 120.96 68.46 (0.81) 39.33, 122.82 67.51 (0.82) 36.93, 157.26
Transferrin saturation (%) 17.04 (2.19) 1.30, 83.96 19.03 (0.60)
0.74, 64.79 20.92 (0.77)
2.35, 85.46 18.35
µ
σ
(0.69) 0.35, 97.03
Serum ferritin (
µ
g/l)
46.69 (39.16) 1.24, 1951.17 31.60*
#
(6.45) 0.28, 1470.70 43.24
+$
(12.66) 0.83, 2678.53 47.16
®@
(6.60) 0.50, 775.58
Hb (g/dl)
12.43 (0.46) 6.67, 31.10 12.05* (0.98) 6.10, 20.90 12.00
+
(0.12) 4.70, 19.80 11.87
®@
(0.12) 5.70, 19.60
*Significant difference between underweight and normal weight before adjusting for age and smoking (
p
<
0.05).
+
Significant difference between underweight and pre-obese before adjusting for age and smoking (
p
<
0.05).
®
Significant difference between underweight and obese before adjusting for age and smoking (
p
<
0.05).
♀
Significant difference between normal weight and obese before adjusting for age and smoking (
p
<
0.05).
µ
Significant difference between pre-obese and obese before adjusting for age and smoking (
p
<
0.05).
#
Significant difference between underweight and normal weight after adjusting for age and smoking (
p
<
0.05).
$
Significant difference between underweight and pre-obese after adjusting for age and smoking (
p
<
0.05).
@
Significant difference between underweight and obese after adjusting for age and smoking (
p
<
0.05).
σ
Significant difference between pre-obese and obese after adjusting for age and smoking (
p
<
0.05). BMI: body mass index, G-Mean: geometric mean,
Hb: haemoglobin, SE: standard error, TIBC: total iron-binding capacity.
