a Medical Research Council Environmental Epidemiology Unit, Southampton SO16 6YD, UK.
b National Public Health Institute, Department of Epidemiology and Health Promotion, Diabetes and Genetic Epidemiology Unit, Mannerheimintie 166, Helsinki, Finland.
c University of Helsinki, Department of Public Health, 00014 Helsinki, Finland.
Correspondence: Professor DJP Barker, MRC Environmental Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, UK. E-mail: djpb{at}mrc.soton.ac.uk
Abstract
Background Low birthweight has been consistently shown to be associated with coronary heart disease (CHD) and its biological risk factors. The effects of low birthweight are increased by slow infant growth and rapid weight gain in childhood. To quantify the importance of developmental processes in the genesis of CHD it is necessary to establish the impact of fetal, infant and childhood growth on major pathological events in later lifedeath, hospital treatment and the need for medication.
Methods Longitudinal study of 13 517 men and women who were born in Helsinki University Hospital during 19241944, whose body sizes at birth and during childhood were recorded, and in whom deaths, hospital admissions, and prescription of medication for chronic disease are documented.
Results The combination of small size at birth and during infancy, followed by accelerated weight gain from age 3 to 11 years, predicts large differences in the cumulative incidence of CHD, type 2 diabetes and hypertension.
Conclusions Coronary heart disease and type 2 diabetes may originate through two widespread biological phenomenadevelopmental plasticity and compensatory growth.
Keywords Fetal growth, childhood growth, type 2 diabetes, hypertension, coronary heart disease
Accepted 11 June 2002
Associations between small body size at birth and during infancy and later cardiovascular disease and its biological risk factors have been found consistently.14 For different risk factors the magnitude of the effects varies. For example, while birthweight is associated with large variations in indices of insulin resistance,5,6 it is associated with small variations in blood pressure.7 A possible explanation for this is that, following an intra-uterine lesion regulatory mechanisms may maintain homeostasis for many years until further damage, due to age, obesity or other influences, initiates a self-perpetuating cycle of progressive functional loss.8 Brenner has proposed such a model for the development of hypertension following reduced nephron numbers at birth, a known correlate of low birthweight.8 In order to quantify the importance of developmental processes in the genesis of cardiovascular disease and type 2 diabetes we need to establish the impact of fetal and infant growth on major pathological events in later life rather than risk factors.
Recent studies have shown that the effect of small body size at birth on later cardiovascular disease and type 2 diabetes is modified by the path of childhood growth.912 In particular, rapid childhood weight gain increases the risk of disease associated with small body size at birth and during infancy. Examination of the risk of disease attributable to early development therefore requires data on fetal, infant and childhood growth. The Hertfordshire studies showed, for the first time, that people who had low birthweight and low weight at age one year were at increased risk of developing coronary heart disease (CHD) and type 2 diabetes;1,13 but the data did not include measurements of height or weight beyond 1 year of age. We have examined the combined effects of fetal, infant and childhood growth in the Helsinki cohort and present data on the magnitude of the effects together with their possible biological interpretation.
Methods
The Helsinki cohort comprises a group of men and women, born 19241933, for whom there are data on size at birth and serial measurements of height and weight through school years; together with another, younger group of men and women born 19341944, for whom there are serial measurements of height and weight from birth.12 The total cohort comprises 15 846 individuals: we present here data for 13 517 men and women, for whom there are measurements of body size both at birth and at age 11 years. In Finland there are national registers of hospital discharges by cause, and registers of people receiving medication for chronic illness, including type 2 diabetes and hypertension, in addition to registers of deaths by cause.912 The registers of people receiving medication are maintained because the costs of medication are reimbursed to the patients. This is subject to the approval of a physician who reviews each case history. The diagnosis of type 2 diabetes is based on World Health Organization criteria.14 Of the estimated 150 000 patients with diagnosed diabetes in Finland 113 000 (75%) are treated with medication.15 It is therefore possible to relate fetal and childhood growth to type 2 diabetes and hypertension defined by prescription of medication,11,12 and to CHD defined by hospital admission or death.9 We identified all people receiving medication for type 2 diabetes and hypertension at any time from 1964 to 1997 and all hospital discharges or deaths from CHD during 1971 to 1997.
We calculated odds ratios for type 2 diabetes and hypertension in the cohort according to birthweight and body mass index (BMI) (weight/height2) at age 11 years. We selected 11 years for comparability with previous studies,11 but the results for adjacent years are similar. In the past boys and girls of these ages in Finland would not yet have reached puberty. The average age of menarche at that time was around 14 years.16 We calculated the odds ratios for men and women combined and adjusted them for year of birth and sex.
We used the cumulative incidence of type 2 diabetes and hypertension to examine the proportion of cases attributable to low birthweight and rapid childhood gain in BMI. We examined change in BMI between age 3 years and age 11 years because type 2 diabetes is associated with low rates of growth up to age 2 years. Age 311 years broadly corresponds to the juvenile phase of growth.16 Use of age 2 or 4 years as the starting point has little effect on the results. The analysis of cumulative incidence was restricted to the people who were born 19341944, for whom growth data were available from birth, through infancy and early childhood and into school years. As described previously,912 we used standard deviation scores to describe growth and divided the subjects into those whose standard deviation score for BMI increased or decreased between the ages of 3 and 11 years.
To correspond with our analyses of type 2 diabetes and hypertension we calculated hazard ratios, adjusted for sex and year of birth, for death and for hospital discharge or death from CHD. We examined the associations with birthweight and BMI at age 11 years in the total cohort of 13 517 men and women. We again used cumulative incidence to examine the associations with birth size and change in BMI between age 3 and 11 years in younger subjects, born 19341944. Among men in the total cohort, ponderal index at birth (birthweight/birth length3) predicted CHD more strongly than birthweight,9 while among women birth length was the strongest predictor.10 We therefore analysed men and women separately using these two different measures of body size at birth.
Results
Type 2 diabetes and hypertension
Table 1 is based on 698 patients being treated for type 2 diabetes and 2997 patients being treated for hypertension in people born 19241944. It shows odds ratios according to birthweight and fourths of BMI at age 11 years. The risks for each disease fell with increasing birthweight and rose with increasing BMI. The odds ratio for type 2 diabetes was 0.67 (95% CI: 0.580.79) for each kilogram increase in birthweight and 1.18 (95% CI: 1.131.23) for each kg/m2 increase in BMI at age 11 years. The corresponding figures for hypertension were 0.77 (95% CI: 0.710.84) and 1.07 (95% CI: 1.041.09).
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Size of effects
Men and women who had birthweights above 4 kg and whose pre-pubertal BMI was in the lowest fourth had around half the risk of type 2 diabetes and hypertension when compared with people who had birthweights below 3 kg but whose BMI was in the highest fourth (Table 1). Disease risk was related to the rate of increase in childhood BMI as well as to the BMI attained at any particular age.11,12 If each individual in the cohort had been in the highest third of birthweight and had lowered their standard deviation score for BMI between age 3 and 11 years (Table 2
) the incidence of type 2 diabetes would have been reduced by 57% and the incidence of hypertension by 25%.
There were similarly strong gradients in risk of CHD, whether defined by death or by hospital admission or death, across groupings of birthweight and BMI at age 11 years (Table 3). Again men and women who had birthweights above 4 kg and whose pre-pubertal BMI was in the lowest fourth had around half the risk of CHD when compared with people who had birthweights below 3 kg but whose BMI was in the highest fourth (Table 3
). If each man in the cohort had been in the highest third of ponderal index at birth, and each woman in the highest third of birth length, and if each man or woman had lowered their BMI score between age 3 and 11 years the incidence of CHD would have been reduced by 25% in men and 63% in women (Table 4
). The number of cases among women is, however, small. Consistent with findings in Hertfordshire1 low weight and BMI at age 1 year were more strongly associated with CHD among men than low birthweight or ponderal index at birth.9 If each man had been in the highest third of BMI at age 1 year, and had lowered his standard deviation score for BMI between age 3 and 11 years the incidence of CHD would have been reduced by 40% (Table 5
).
The large reductions in disease incidence that we have shown to be associated with modest alterations in fetal, infant and childhood growth may be underestimates. As Robinson17 wrote, birthweight and ponderal index (as well as body mass index) are crude measures of how fetal nutrition has affected body composition, so the true size of the effect of fetal growth on later disease is hard to measure.
Biological basis
Since McCance and Widdowsons pioneering observations in Cambridge,18,19 experimentalists have repeatedly demonstrated that minor alterations to the diets of pregnant animals can produce lasting changes in the offsprings physiology and metabolism.20,21 That this should be so is unsurprising. So-called phenotypic plasticity enables one genotype to give rise to a range of different physiological or morphological states in response to different environmental conditions during development.22,23 Such gene-environment interactions are ubiquitous in the development of all living things. The benefit of developmental plasticity is that, in a changing environment, it enables the production of phenotypes that are better matched to their environment than would be possible by the production of the same phenotype in all environments.23
The different size of newborn human babies exemplifies plasticity. The growth of babies has to be constrained by the size of the mother, otherwise normal birth could not occur. Small women have small babies:24 in pregnancies after ovum donation they have small babies even if the woman donating the egg is large.25 Babies may be small because their growth is constrained in this way or because they lack the nutrients for growth. As McCance wrote long ago, The size attained in utero depends on the services which the mother is able to supply. These are mainly food and accommodation.26 Since mothers height or pelvic dimensions are generally not found to be important predictors of chronic disease in later life,27,28 research into the fetal origins of disease has focussed on the nutrient supply to the baby. The central concept is that despite current levels of nutrition in Western countries the nutrition of many fetuses and infants remains sub-optimal because the nutrients available are unbalanced or because their delivery is constrained by the long and vulnerable fetal supply line.29 Size at birth for gestational age serves as a marker of fetal nutrition.30
When undernutrition during early development is followed by improved nutrition many animals and plants stage accelerated or compensatory growth.31 Compensatory growth has costs, however, which in animals include reduced life-span.31 One suggestion is that a higher rate of cell division causes more rapid shortening of the protective ends of the chromosomes (telomeres) and hastens cell death and organ degradation.32 There are a number of other possible processes by which, in humans, undernutrition and small size at birth followed by rapid childhood growth could lead to cardiovascular disease and type 2 diabetes in later life.9,11,12 The Helsinki cohort has shown that people who were small at birth and had rapid growth thereafter are not only physiologically and morphologically different, but also have altered responses to poor living standards in later life.33
Conclusion
Our findings suggest that a substantial part of the risk of CHD, type 2 diabetes and hypertension is established during development. We suggest that this reflects two widespread biological phenomena, developmental plasticity and compensatory growth.
KEY MESSAGES
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Acknowledgments
Funding: British Heart Foundation, Jahnsson Foundation, Finska Läkaresällskapet.
References
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