2
.
5
. Statistical analysis The results are expressed as means 9 S.D. Serum
triglyceride concentrations were log-transformed for statistical analyses because of skewness of the data.
Differences between two groups were tested with a two-sample t-test. One- or two-way analysis of variance
was used in analyses of overall differences between the apo E phenotypes. In some analyses, subjects with apo
E34 and 44 phenotypes were analysed together as the apo E4
+
group. Similarly, in some analyses apo E23 and apo E33 children were combined to form the apo
E4
−
group. Pearson’s correlation coefficient r was calculated for serum triglyceride values at the two age
points and for correlation between concentrations of serum HDL cholesterol and triglycerides. P-values B
0.05 were considered significant. Statistical analyses were performed using SAS release 6.12 program pack-
age SAS Institute, Cary, NC.
3. Results
The apo E allele frequencies in the groups of infants at the age of 7 and 13 months were identical o2, 0.06;
o3, 0.74; and o4, 0.20 Table 1. Only four and six infants had apo E22 phenotype and only 18 and 22
infants had apo E24 phenotype at the ages of 7 and 13 months, respectively. The non-fasting serum triglyceride
concentration mean 9 S.D. in the apo E22 infants was 2.75 9 1.96 and 1.42 9 0.60 mmoll at the ages of 7
and 13 months, respectively. Similarly, the mean con- centration in the apo E24 infants was 1.87 9 0.63 and
1.69 9 0.74 mmoll, respectively. Because of the small number of infants with these apo E phenotypes, they
were excluded from further analyses. The mean time interval between infant’s previous
meal and drawing of the blood sample did not correlate with measured serum triglyceride concentrations at the
ages of 7 and 13 months r = − 0.002, P = 0.96 and r = − 0.01, P = 0.80, respectively. Further, the mean
time interval and serum triglyceride values showed no correlation in the apo E4
+
infants r = 0.02, P = 0.81 for infants aged 7 months and r = − 0.05, P = 0.43 for
infants aged 13 months and in the apo E4
−
infants r B 0.01, P = 0.94 for infants aged 7 months and r =
− 0.06, P = 0.17 for infants aged 13 months. Also, no
correlation was observed when infants with the four main apo E phenotypes were studied separately at these
age points data not shown. The mean non-fasting serum triglyceride concentra-
tion was higher at the age of 7 than at 13 months 1.72 9 0.92 vs 1.47 9 0.74 mmoll. In those 671 infants
whose samples were successfully measured at both age points, serum triglyceride concentration decreased by
0.27 9 1.05 mmoll P = 0.0001 during the 6-month follow-up. The serum triglyceride concentrations at 7
and 13 months of age correlated r = 0.21, P = 0.0001 in these 671 children despite the fact that the time
interval between the previous meal and drawing the blood sample varied randomly at both ages.
Girls had higher mean non-fasting serum triglyceride concentration than boys at the age of 7 months 1.79 9
0.95 vs 1.65 9 0.89 mmoll, P = 0.02 as well as at 13 months 1.55 9 0.78 vs 1.39 9 0.69 mmoll, P = 0.0002.
As serum triglyceride values and apo E phenotypes associated similarly in the girls and boys, the genders
were combined in further analyses.
The apo E4
+
infants had higher non-fasting serum triglyceride concentration than the apo E4
−
infants both at 7 and 13 months of age. Stratification of serum
triglyceride values according to apo E phenotypes
Table 1 Characteristics of the study subjects at the ages of 7 and 13 months
E4
−
E4
+
E44 E34
E33 E23
At
7
months 245
36 209
412 66
N 478
33.9 5.0
28.9 57.0
9.1 Proportion of study infants
a
66.1 18
115 188
Females, n 31
219 133
35 94
18 224
112 Male, n
259 3.17 9 8.30
5.58 9 8.06 2.98 9 8.74
1.98 9 8.30 Relative weight
b
2.52 9 8.35 3.01 9 8.67
At
13
months 276
555 477
228 N
48 78
66.8 33.2
5.8 27.4
Proportion of study infants
a
57.4 9.4
152 258
220 125
Females, n 27
38 40
257 103
Males, n 21
297 124
1.14 9 7.46 2.03 9 8.15
1.51 9 7.66 Relative weight
b
1.96 9 8.08 1.59 9 7.63
3.68 9 8.14
a
Infants with apo E22 or apo E24 phenotype are excluded.
b
Values are means 9 S.D. Relative weight is expressed as deviation in percentage from the mean weight of healthy Finnish children of same height and sex. For the overall differences in relative weight between the four different apo E phenotypes at the ages of 7 and 13 months P = 0.11
and 0.51, respectively one-way analysis of variance.
Table 2 Non-fasting serum triglyceride concentration mmoll in 7- and 13-month-old infants stratified according to apo E phenotype
a
E33 E34
E23 E44
E4
+
E4
−
At
7
months 1.63 9 0.90
Mean 9 S.D. 1.81 9 0.90
1.71 9 0.83 2.05 9 1.24
1.84 9 0.96 1.64 9 0.89
1.40 0.40–6.77 1.63 0.50–6.30
1.70 0.60–7.10 1.60 0.32–4.60
1.70 0.50–7.10 Median range
1.40 0.32–6.77 0.009
b
0.01
b
P-value 0.002
c
0.42
b
At
13
months Mean 9 S.D.
1.35 9 0.72 1.43 9 0.76
1.52 9 0.67 1.69 9 0.74
1.55 9 0.69 1.42 9 0.76
1.30 0.30–7.00 1.40 0.40–4.40
1.70 0.60–4.20 1.10 0.40–3.90
1.40 0.40–4.40 Median range
1.20 0.30–7.00 0.02
b
0.008
b
P-value 0.001
c
0.39
b a
E4
+
group is apo E34 and 44 infants combined, E4
−
group is E23 and E33 infants combined.
b
P-values refer to comparisons between the values of the apo E33 infants and infants with other phenotypes one-way analysis of variance.
c
P-values refer to comparisons between the values of the E4
+
infants and E4
−
infants two-sample t-test. Table 3
Non-fasting serum triglyceride concentration mmoll in E4
+
and E4
−
infants stratified according to milk type used at the age of 7 months and stratified according to randomised group in the STRIP project intervention or control at the age of 13 months
a
Breast milk+formula Breast milk only
Formula only E4
−
E4
+
E4
−
E4
+
E4
−
E4
+
At
7
months N
92 169
47 78
106 231
1.76 9 0.91 1.94 9 1.04
1.63 9 0.99 Mean 9 S.D.
1.77 9 0.83 1.53 9 0.79
1.68 9 0.84 0.40–6.77
0.60–4.70 0.50–4.60
0.60–6.30 0.50–7.10
0.32–5.60 range
Intervention Control
E4
−
E4
+
E4
−
E4
+
At
13
months 297
146 258
130 N
1.58 9 0.74 1.44 9 0.77
Mean 9 S.D. 1.40 9 0.75
1.52 9 0.64 0.40–7.00
range 0.50–4.20
0.40–4.40 0.30–6.70
a
At the age of 7 months, apo E4 phenotype associated with serum triglyceride values P = 0.01, whereas milk type showed no such association with triglyceride values P = 0.34. For the interaction term milk×phenotype, P = 0.95 two-way analysis of variance. At the age of 13 months,
apo E4 phenotype associated with serum triglyceride values P = 0.005, whereas the group intervention or control showed no such association with serum triglyceride values P = 0.29. For the interaction term intervention×phenotype, P = 0.40 two-way analysis of variance.
showed that the infants with apo E44 had the highest serum triglyceride concentration, and the triglyceride
values declined in the order E44 \ E34 \ E33 Table 2.
At 7 months of age, multivariate analysis with serum triglyceride concentration as the dependent variable
and apo E4 phenotype E4
+
or E4
−
and milk type breast milk or formula as the independent variable
showed that the apo E4 type independently associated with non-fasting serum triglyceride concentration,
whereas milk type showed no such association Table 3. Consequently, data on infants fed solely breast
milk, breast milk and formula, or solely formula were combined for further analyses.
Non-fasting serum triglyceride values in infants aged 13 months showed no association with the group to
which they were randomised intervention group or control group in a covariance analysis with triglyce-
ride values as a dependent variable and treatment group and apo E4 type as covariates. Meanwhile, the
apo E4 phenotype associated with serum triglyceride values Table 3. Consequently, data on the interven-
tion and the control infants were combined for further analyses.
The relative weights of infants with different apo E phenotypes were closely similar Table 1. When the
infants were divided according to relative weight ter- tiles, the E4
−
infants in the heaviest tertile had the highest mean serum triglyceride concentration at the
age of 7 months Table 4. Apo E4 phenotype influ- enced serum triglyceride values in a multivariate analy-
sis including apo E4 phenotype and relative weight tertile. The relative weight tertile also had an effect on
serum triglyceride values at the age of 7 months, but not at 13 months. The multivariate analysis showed no
weight × apo E phenotype interaction.
The o4 allele also had an effect on serum HDL cholesterol concentration in these infants. Serum HDL
cholesterol concentration was lower in the infants with o4 allele than in those without the allele at 7 months of
age 0.88 9 0.19 vs 0.92 9 0.19 mmoll, respectively; P = 0.03 and again at 13 months of age 0.86 9 0.18 vs
0.90 9 0.19 mmoll; P = 0.003. Concentrations of serum HDL cholesterol and triglycerides showed a
moderate correlation in the apo E4
+
infants r = − 0.34, P = 0.0001 and in the apo E4
−
infants r = − 0.37, P = 0.001 at the age of 7 months. Similar
correlations were found at the age of 13 months r = − 0.35, P = 0.0001 for the apo E4 infants and r = − 0.31,
P = 0.0001 for the apo E4
−
infants. We have earlier shown that in the whole STRIP
study material, the mean concentration of serum total cholesterol is higher in infants with apo E4
+
phenotype than in infants with apo E4
−
phenotype [8]. Similarly, in the present substudy in the infants from whom serum
triglyceride value was available, the concentration of serum total cholesterol was higher in the apo E4
+
infants than in the apo E4
−
infants 4.12 9 0.82 vs 3.90 9 0.73 mmoll, P = 0.0001 at 7 months of age and
at 13 months of age 4.26 9 0.73 vs 4.01 9 0.73 mmoll, P = 0.0001.
4. Discussion
