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J G Eriksson a National Public Health Institute,
Department of Epidemiology and Health Promotion, Diabetes and Genetic
Epidemiology Unit, Mannerheimintie 166, FIN-00300 Helsinki, Finland, b Medical Research Council Environmental Epidemiology Unit,
University of Southampton, Southampton General Hospital, Southampton
S016 6YD
Correspondence to: Professor Barker
david.barker{at}mrc.soton.ac.uk
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Abstract |
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Objective:
To examine whether catch-up growth during childhood modifies the increased risk of death from coronary heart disease that is associated with reduced intrauterine growth.
Design:
Follow up study of men whose body size at birth was recorded and who had an average of 10 measurements taken of
their height and weight through childhood.
Setting:
Helsinki, Finland.
Subjects:
3641 men who were born in Helsinki
University Central Hospital during 1924-33 and who went to school in Helsinki.
Main outcome measures:
Hazard ratios for death from
coronary heart disease.
Results:
Death from coronary heart disease was
associated with low birth weight and, more strongly, with a low
ponderal index at birth. Men who died from coronary heart disease had
an above average body mass index at all ages from 7 to 15 years. In a
simultaneous regression the hazard ratio for death from the disease
increased by 14% (95% confidence interval 8% to 19%; P<0.0001) for
each unit (kg/m3) decrease in ponderal index at birth and
by 22% (10% to 36%; P=0.0001) for each unit (kg/m2)
increase in body mass index at 11 years of age. Body mass index in
childhood was strongly related to maternal body mass index, which in
turn was related to coronary heart disease. The extent of crowding in
the home during childhood, although related to body mass index in
childhood, was not related to later coronary heart disease.
Conclusion:
The highest death rates from coronary
heart disease occurred in boys who were thin at birth but whose weight caught up so that they had an average or above average body mass from
the age of 7 years. Death from coronary heart disease may be a
consequence of poor prenatal nutrition followed by improved postnatal nutrition.
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Key messages
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Introduction |
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People who had low birth weight, or who were thin or short at
birth as a result of reduced intrauterine growth, have increased rates
of coronary heart disease.
1 2
They also have an increased prevalence of biological risk factors for the disease
namely, hypertension, non-insulin dependent diabetes, and abnormalities in
lipid metabolism and blood coagulation.
3 4
These
associations have been replicated in studies in a number of
countries.5-8 They have led to the hypothesis that
coronary heart disease originates in utero through the persistence of
endocrine, physiological, and metabolic adaptations that the fetus
makes when it is undernourished.4
We do not yet know whether the increased risk of coronary heart
disease associated with reduced prenatal growth is modified by
growth during childhood. This may be important because optimising childhood growth through improved nutrition and living conditions might
reduce the risk of the disease. We have previously described associations between size at birth and death from coronary heart disease in a cohort of men born in Helsinki, Finland, during 1924 to
1933.9 The growth of these men through childhood, and
their living conditions, were recorded. The men had an average of 10 serial measurements taken of height and weight between the ages of 7 and 15 years. This allowed us to examine, for the first time, the
association between childhood growth and death from coronary heart
disease, taking into account size at birth.
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Subjects and methods |
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We studied a sample of men who were born at the
Helsinki University Central Hospital and who went to school in
Helsinki. Details of the birth records kept in the hospital have been
described.9 Data on the mothers consisted of age, parity,
height, date of the last menstrual period, and age at menarche,
together with body weight measured on admission in labour. Data on
their newborn babies consisted of birth weight, placental weight, and
length and head circumference. We studied men who were born at the
hospital during 1924 to 1933, who went to school in Helsinki, and who
were still resident in Finland in 1971. School health records for all
children attending schools in Helsinki are stored in the city archives.
We identified 3975 men from the birth and school health records, and we
used the population register that covers the whole Finnish
population to trace 3641 (92%) of them. The mean birth size of men who
were traced and not traced was similar. This cohort comprised 339 more
men than were included in our first report because further information
has allowed linkage of additional birth and school records.
Protocol
For each of the 3641 men there was an average of
10 (SD 4) measurements of height and weight between the ages of 6 and
16 years, giving a total of 37 939 measurements. These were recorded
during periodic school medical examinations. At the first examination,
most commonly at the age of 7 years, school nurses recorded the number
of other people living in the child's house, and the number of rooms.
Since 1971 all residents of Finland have been assigned a unique
personal identification number. By using this number we identified all
deaths among the men during 1971-95. Deaths in Finland are recorded in
the national mortality register. The register was computerised in 1971, and causes of death were recorded according to ICD-8 (international
classification of diseases, eighth revision) until 1986; thereafter
ICD-9 was used until the end of 1995. The first three digits from the
primary cause of death in ICD-8 and ICD-9 were used for identifying
deaths from coronary heart disease (410-414). Using the father's
occupation, which was on 3375 of the birth records, we grouped the men
according to a social classification used by the Central Statistical
Office. Overall, 84% (2836) of the fathers were labourers and 11.5%
(387) were classified as lower middle class. Together these constitute the lower social class as opposed to the upper social class, which is
subdivided into upper middle class (2.6%, 86) and self employed (1.6%, 55).
Statistical analysis
The number of deaths from coronary
heart disease was compared with that expected from Finnish national
rates for men of corresponding age and year of birth. Death rates were
expressed as standardised mortality ratios, the national average being
100. We examined the trends in standardised mortality ratios with
neonatal measurements. Tests for trend were based on the corresponding log linear model and on Cox's proportional hazards model, using either
continuous or categorical variables and their interactions. We
converted each measurement for height, weight, and body mass index for
each boy to a Z score, using the method of Royston.10 We
interpolated between successive Z scores with a piecewise linear function and so obtained a Z score at each birthday from 7 to 15 years
of age. We back transformed these Z scores to obtain the corresponding
height, weight, and body mass index at these ages.
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Results |
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Table 1 shows the maternal, neonatal, and childhood characteristics of the 3641 men. Overall, 1084 (30%) of the men had died, 310 (8.5%) from coronary heart disease. The mean age at death from coronary heart disease was 58 years (range 38 to 71 years), and the standardised mortality ratio was 83 (95% confidence interval 74 to 93).
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Table 2 shows hazard ratios for coronary heart disease according to size at birth. The ratios decreased with
increasing birth weight, although this was not statistically significant. As we have previously described,9 ratios
decreased more steeply with increasing ponderal index (birth
weight/length3). The ratios also decreased with increasing
placental weight. There were no trends with head circumference or
length at birth. Hazard ratios were not related to the length of
gestation, although the highest ratios were in men born after 41 weeks.
After adjustment for the length of gestation, the associations with
birth weight and ponderal index strengthened (table 2), and there was a
significant association with placental weight
(P=0.03).
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Growth in childhood
From 7 to 15 years of age the average height of men who died from
coronary heart disease was similar to that of the other men in the
cohort. Figure 1 shows, however, that at every age the men who died
from coronary heart disease had a higher body mass index than the
other men in the cohort. The association was stronger in older
children, many of whom would have experienced puberty. The association
was strengthened by adjustment for ponderal index at birth, because
babies born with a low ponderal index tended to have a low body mass
index throughout childhood. The correlation between ponderal index at
birth and body mass index at age 11 years, for example, was 0.18 (P<0.0001). The adjusted hazard ratio for death from coronary heart
disease associated with a 1 SD increase in body mass index was 1.15 (1.03 to 1.29) at 7 years of age and 1.18 (1.07 to 1.31) at 15 years of
age.
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The mothers' body mass indices
were strongly and inversely related to their age at menarche and
strongly positively related to the height and body mass index of their
sons (P<0.0001 for body mass indices at all ages). As described in our
previous report, high maternal body mass was also strongly related to
increased hazard ratios for coronary heart disease among the men, an
effect which was confined, however, to mothers of below average stature (<1.58 m).9 The effect of maternal body mass index on
coronary heart disease was only partly dependent on its effect on body mass in childhood. In a simultaneous regression the hazard ratios for
coronary heart disease increased by 15% (3% to 28%; P=0.02) for
every SD increase in maternal body mass index, and by 13% (1% to
26%; P=0.03) for every SD increase in body mass index at 11 years of age.
Crowding in the home and social class during
childhood
Table 1 shows the average number of inhabitants and
rooms in the homes where the men grew up; 46% (1435) lived in homes
with only one room. We used the ratio of the number of inhabitants to
the number of rooms as an index of crowding. Table 4 shows that
families living in less crowded homes were of higher social class, and
the sons were taller and had a higher body mass index at 11 years of
age. The results at ages other than 11 years were similar. We used
multiple linear regression to examine the simultaneous effects of the
mother's body mass index and crowding on the boy's body mass index at
11 years of age. The effect of the mother's body mass was much
stronger (P<0.0001) than that of crowding (P=0.01). Death from
coronary heart disease was unrelated to the number of inhabitants or
rooms or to crowding; in a simultaneous analysis it remained unrelated
whereas the association with increased mothers' body mass was
significant (P=0.003).
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Discussion |
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In Finland, men who had low birth weight and were thin at birth, but had an above average body mass in childhood, had high death rates from coronary heart disease. The association between coronary heart disease and size at birth in these men was consistent with findings in two cohorts in the United Kingdom, totalling 13 249 men,2 and in a cohort of 7012 men in Sweden.5 The association was strengthened by adjustment for length of gestation.
We were able to trace 92% of the men in the cohort. Our study was restricted to men who were born in Helsinki University Central Hospital and who went to school in Helsinki. The fathers of 84% of the men were classed as labourers. The men may be unrepresentative of all men living in Helsinki, although we know that early this century around 60% of men in the city were labourers.11 Likewise, the exceptionally overcrowded conditions in which the men grew up (46% having only one room in their homes) may not be typical of the city at that time. This would introduce a bias, however, only if the association between size at birth, childhood growth, and coronary heart disease differed between those born in the hospital and those born outside the hospital. We did not find an association between coronary heart disease and short stature, as has been found in studies of adults and in a cross sectional study of children.12-14 This may reflect the short average stature and poor living conditions of all the men in our cohort, whose average height at 11 years was 1 SD below the mean for current growth charts in Finland.
Catch-up growth
Our study gives a unique picture of the fetal and childhood
growth of men who were born in the early years of this century in poor
socioeconomic conditions and who died from coronary heart disease. Men
with the highest rates of the disease were thin at birth, but by
the age of 7 years their weight had "caught up" and their body
mass index was above average. Thereafter, up to 15 years of age,
their body mass index tended to diverge further from the average. The
association between a high body mass index in childhood and death
from coronary heart disease is consistent with the known adverse
effects of a high body mass index in adults.
15 16
It is
also consistent with previous studies showing that high body mass
index in childhood is related to increased death rates from all causes
combined and from coronary heart disease.17-19
Childhood nutrition and living conditions
Whatever the mechanisms, our findings show that the
combination of retarded fetal growth and accelerated weight gain
between birth and 7 years of age is associated with a large increase in
risk of death from coronary heart disease in men. The data suggest that
accelerated weight gain among the men in our study resulted from good
nutrition rather than from good living conditions with relative freedom
from recurrent infection. The body mass indices of the boys were
related to their mothers' body mass indices, as has been found in
other studies.
27 28
We found that the mother's body mass
index, which was measured in pregnancy, was inversely associated with
age at menarche. Since menarcheal age is determined mainly by
prepubertal body weight,29 this association shows that
body mass in pregnancy reflected the mother's prepubertal growth and
nutrition as well as her nutrition as an adult and her pregnancy weight
gain. We conclude that death from coronary heart disease among the men
in our study reflected the combination of poor prenatal nutrition with
improved postnatal nutrition which was linked to their mothers having a
high body mass. We do not know whether mothers with a high body mass
influenced the postnatal catch-up growth of their children through
direct effects during lactation or through better availability of food after weaning. Neither do we know the age before 7 years when catch-up
in weight occurred. A child's body mass index decreases from infancy
until around 6 years, and then increases.30 This increase
is called the adiposity rebound, and later obesity may be related more
to the timing of the rebound than to the subsequent energy intake.
In a previous report on
this cohort, we described high death rates from coronary heart disease
in men who were thin at birth but whose mothers were overweight in
pregnancy. We concluded that overweight mothers afforded an adverse in
utero environment, especially for fetuses whose development was
constrained by poor placental growth. We have now identified that thin
neonates are further disadvantaged if they have accelerated
postnatal weight gain as a result of good nutrition. This may give
further insight into the circumstances that lead to coronary heart
disease epidemics in previously malnourished communities. The immediate
consequence of improved nutrition is that not only mothers' body mass
indices but also children's body mass indices increase, whereas fetal nutrition remains limited by intergenerational constraints on placental
growth. These changes are associated with a steep increase in coronary
heart disease. Programmes to reduce obesity among boys may therefore
usefully focus on those who had low birth weights or were thin at
birth, and who therefore increase their risk of death from coronary
heart disease by becoming even slightly overweight in childhood.
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Acknowledgments |
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We thank Terttu Nopanen, Tiina Saarinen, Hillevi Öfverström-Anttila, Liisa Toivanen, Arja Purtonen, Tiina Valle, Hanna Pehkonen, and Ulla Tarvainen for abstracting the data from the records. Sigrid Rosten was responsible for data management.
Contributors: All the authors took part in the design and analysis of the study and jointly wrote the paper. The data abstraction and linkage were supervised by JGE and TF. JGE, CO, and DJPB will act as guarantors for the paper.
Funding: British Heart Foundation, Jahnsson Foundation, Finska Läkaresällskapet, Orion Corporation Research Foundation, and Finnish Foundation for Cardiovascular Research.
Competing interests: None declared.
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References |
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specific explanations of a general pattern?
Lancet
1984;
i:
1003-1006.
follow-up of the Carnegie survey of diet and growth in pre-war Britain.
J Epidemiol Community Health
1996;
50:
580-581(Accepted 5 December 1998)
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