The role of size at birth and postnatal catch-up growth in determining systolic blood pressure: a systematic review of the literature

Decreased endothelium-dependent NO-cGMP vascular relaxation and hypertension in growth-restricted rats on a high-salt diet

Low birth weight caused by placental insufficiency increases the risk of hypertension in young adults, particularly while ingesting a high-salt diet; however, the vascular mechanisms involved are unclear. We tested whether intrauterine fetal growth restriction results in salt-sensitive offspring that exhibit impaired endothelium-dependent relaxation, enhanced vascular contraction, and hypertension during high-salt diet feeding. Male offspring of control pregnant rats and pregnant rats with reduced uterine perfusion pressure (intrauterine growth restricted [IUGR]) were fed either a normal-sodium (NS, 1%) or a high-sodium (HS, 8%) diet. Body weight was less in IUGR/NS and IUGR/HS than in NS and HS rats. Arterial pressure was greater in IUGR/NS (144+/-4 mm|Hg) than in NS (131+/-3 mm|Hg) rats and far greater in IUGR/HS (171+/-12 mm|Hg) than in HS (129+/-2 mm|Hg) rats. In isolated, endothelium-intact aortic strips, phenylephrine (Phe, 10(-5) mol/L) caused an increase in active stress that was greater in IUGR/NS (13.9+/-0.9 N/m2) than in NS (8.5+/-0.6 N/m2) animals and far greater in IUGR/HS (18.2+/-1.2 N/m2) than in HS (9.4+/-0.8x10(4) N/m2) rats. Acetylcholine caused relaxation of the Phe-mediated contraction and induced vascular nitrite/nitrate production that was less in IUGR/NS than in NS animals and far less in IUGR/HS than in HS rats. N(G)-nitro-L-arginine methyl ester, which inhibits nitric oxide (NO) synthase, or ODQ, which inhibits cGMP production in smooth muscle, inhibited acetylcholine relaxations and enhanced Phe contractions in NS and HS rats but not in IUGR/NS or IUGR/HS rats. Endothelium removal enhanced Phe-induced stress in NS and HS rats but not in IUGR/NS or IUGR/HS rats. Thus, endothelium-dependent relaxation via the NO-cGMP pathway is inhibited in systemic vessels of IUGR rats, particularly during intake of an HS diet. This might explain the increased vasoconstriction and arterial pressure in low-birth-weight offspring during ingestion of an HS diet.

A Consistent Abnormality in the Average Local Smoothness of Fetal Heart Rate in Growth-Restricted Fetuses Affected by Severe Pre-Eclampsia

An abnormality in cardiovascular regulation during the prenatal period has been suggested to be the pathophysiological link between fetal growth restriction and adult hypertension. The purpose of this study was to determine how consistently abnormal the local smoothness of the very-short-term heart rate is in growth-restricted fetuses associated with severe pre-eclamptic pregnancy. Multifractal Hurst analysis on the structure function of heart rate was performed in control fetuses (n =150), in fetuses affected by severe pre-eclampsia and not showing growth restriction (n =66) and in fetuses affected by severe pre-eclampsia and showing growth restriction (n =58). The very-short-term (< or =15 heart beats) generalized Hurst exponents of the order of -5 to 5 in three groups were compared. Each exponent quantifies an average local heart rate smoothness at 15-successive-heart rate sites, which were specified by the magnitude of the heart rate variation within the sites determined by and positively correlated with the order of the exponent. This means that the fetal heart rates within the sites of q > or =2 have a large fetal heart rate (FHR) variation, and those within the sites of q < or =-2 have a small FHR variation. In the fetuses affected by severe pre-eclampsia and not showing growth restriction, only values of the exponents of the order > or =2 were abnormally lower. In the fetuses affected by severe pre-eclampsia and showing growth restriction, the values of the exponents of all orders were abnormally lower. In conclusion, the local smoothness of heart rate is consistently abnormal regardless of the magnitude of heart rate variation within a very-short-term period in growth-restricted fetuses affected by severe pre-eclampsia.

Historic and early life origins of hypertension in Africans

Cardiovascular disease (CVD) causes 12.4 million deaths annually, most (9.6 million) occurring in developing countries. Hypertension, the most common CVD, arises within the context of obesity, but the underlying mechanisms remain obscure. Obesity and salt intake are two important risk factors for hypertension and are the focus of this paper. Traditional African populations show a low prevalence of hypertension, but hypertension is more common in migrant African populations in the West than in other ethnic groups. One explanation is genetic, but no causative gene has been confidently identified. Nongenetic susceptibilities such as fetal programming are an alternative explanation. Hypothetically, fetal programming induced by transient stimuli permanently alters fetal structure and function at the cellular, organ and whole-body levels. Birth weight is inversely related to blood pressure and hypertension risk, suggesting that susceptibility to hypertension risk factors such as obesity and salt sensitivity are themselves programmed. In support of this hypothesis, obesity (especially central obesity) is also inversely related to size at birth. Likewise, salt sensitivity might derive from undernutrition in utero, reducing the nephron number and resetting the pressure-natriuresis curve rightward. However, no robust human data or evidence of enhanced salt sensitivity among African-origin populations exist. In the United States, blacks have a greater prevalence of low birth weight than whites, suggesting that the higher prevalence of hypertension among blacks is related to fetal programming. Nevertheless, we need to be scrupulous in ascribing risk to the myriad other confounders of this relationship, including environmental and behavioral correlates of ethnicity, before concluding that excess risk of hypertension in Africans is programmed in utero.

Effect of nutritional restriction in early pregnancy on isolated femoral artery function in mid-gestation fetal sheep

Unbalanced maternal nutrition affects fetal endocrine and cardiovascular systems, sometimes accompanied by changes in growth, although this is usually in late gestation. We determined the effect of moderate restriction for the first half of gestation of maternal dietary protein, or of total calorific intake on isolated resistance artery function of mid-gestation fetal sheep. Welsh Mountain ewes were nutritionally restricted by 30 % of the recommended nutrient intake (globally restricted) or 30 % of the recommended protein intake (protein-restricted), compared to control ewes fed 100 % of recommended nutrient intake, for ~12 days prior to conception and for the subsequent 70 days of gestation. At mid-gestation, fetal and placental weights were similar in all dietary groups. In isolated femoral arteries, the response curve to noradrenaline was reduced in protein-restricted group fetuses (P < 0.05). Maximal relaxation (P < 0.01) and sensitivity (P < 0.05) to acetylcholine were markedly reduced in protein-restricted group fetuses, and to a smaller extent in globally restricted group fetuses (response curve, P < 0.05). The dilator response (P < 0.05) and sensitivity (P < 0.05) to the alpha2 agonist UK14304 was lower in protein-, but not in globally restricted group fetuses. The response (P < 0.05) and sensitivity (P < 0.05) to the nitric oxide donor sodium nitroprusside were reduced in protein-restricted group fetuses compared to controls. Our data show that dietary imbalance, in particular restricted protein, of the ewe can produce blunting of endothelial-dependent and -independent relaxation in systemic arteries from the mid-gestation fetus. These changes may precede perturbed late-gestation fetal and postnatal cardiovascular control.

The association between birthweight and current blood pressure: a cross‐sectional study in an Australian Aboriginal community

OBJECTIVES

To study the relationship of blood pressure to birthweight and current body mass index in a population with high rates of low birthweight (< 2.5 kg).

DESIGN

A cross-sectional population screening program conducted between 1992 and 1998, with retrospective retrieval of birthweights.

SETTING

A remote coastal Australian Aboriginal community with a high prevalence of diabetes, cardiovascular and renal disease.

PARTICIPANTS

Eighty-two per cent of the community members (1473/1805) were screened. Birthweights were available for 767 (71%) of the screened participants aged 7-43 years.

MAIN OUTCOME MEASURES

The association between birthweight and current blood pressure, accounting for current body mass index.

RESULTS

Mean birthweights were low, and 18% of children and 35% of adults had been low-birthweight babies. In children (7-17 years), blood pressure was not correlated with birthweight, but in adults there was an inverse correlation - a 1 kg increase in birthweight was associated with a 2.9 mmHg (95% CI, 0.3-5.5 mmHg) decrease in systolic blood pressure, after adjusting for age, sex and current weight. Overweight adults with low birthweight had the highest blood pressures.

CONCLUSIONS

Low birthweight is significantly associated with higher blood pressure in adult life, and the effect is amplified by higher current weight. Given the high rates of low birthweight in Aboriginal people in remote areas, and the detrimental effect of higher blood pressures on chronic diseases (currently present in epidemic proportions), interventions should focus on improving birthweights and on weight control in adolescents and adults. Special attention should be paid to children with low birthweight to avoid their becoming overweight in adult life.

Coronary heart disease: a disorder of growth

A new 'developmental' model for the origins of coronary heart disease and the related disorders of type 2 diabetes, hypertension and stroke is emerging. The finding that people who develop these disorders have altered growth in utero, during infancy and childhood provides a new starting point for research. The immediate prospect for prevention is through protecting infant growth and preventing accelerated weight gain in children made vulnerable to later disease by small size at birth and during infancy. Ultimately we need to optimize maternal diet and composition before and during pregnancy. Despite current levels of nutrition in Western countries the nutrition of many fetuses and infants remains suboptimal because the nutrients available are unbalanced or because their delivery is constrained by the long and vulnerable fetal supply line.

Weight at birth and subsequent risk of preeclampsia as an adult

OBJECTIVE

We examined the influence of maternal birth weight on the risk of the development of preeclampsia, a likely precursor to adult chronic disease.

STUDY DESIGN

This hospital-based case-control study included 181 preeclampsia cases and 349 control subjects. Participants provided information about their birth weight and other covariates that included medical and reproductive history, prepregnancy weight, and adult height. Odds ratios and 95% CIs were estimated by logistic regression.

RESULTS

The risk of preeclampsia decreased as maternal birth weight increased (P=.01). After an adjustment was made for confounders, data showed that women with a low birth weight (<2500 g) had a 2.3-fold increased risk of experiencing preeclampsia (95% CI, 1.0-5.3) as compared with women who weighed 2500 to 2999 g at birth. Conversely, women with a birth weight of >/=4000 g appeared to have a nonstatistically significant, but >50%, reduction in the risk of experiencing preeclampsia (95% CI, 0.2-1.2). This relationship differed for lean and overweight women (body mass index, <25 kg/m(2) vs >/=25 kg/m(2)). Among lean women, those who were low birth weight had a near doubling in risk of the development of preeclampsia (odds ratio, 1.9; 95% CI, 0.8-4.6), although this association did not reach statistical significance. However, among overweight women, those women who weighed <2500 g at birth had an almost 4-fold increased risk of experiencing preeclampsia (odds ratio, 3.8; 95% CI, 1.1-13.8).

CONCLUSION

These results confirm two earlier reports and expand the literature by showing that women who are small at birth and who become overweight as adults are at particularly high risk of the development of preeclampsia.

Birthweight, childhood social class, and change in adult blood pressure in the 1946 British birth cohort

BACKGROUND

The negative effect of birthweight on systolic blood pressure has been suggested to be initiated in utero and amplified with age. We aimed to investigate this hypothesis.

METHODS

A sample of 3634 people from a birth cohort study of men and women born in Britain in 1946 were included in analyses. Cohort members have been contacted regularly since birth, and systolic and diastolic blood pressures were measured at ages 36, 43, and 53 years. Multilevel models, with blood pressure as a repeated outcome, were used to test the amplification hypothesis and to compare results for birthweight with those for childhood social class.

FINDINGS

Considering both men and women together, a consistent negative association between birthweight and systolic blood pressure was noted from age 36 to 53 years, but no evidence was recorded of substantial amplification with age. A 1 kg higher birthweight was associated with a slower mean increase in systolic blood pressure by -0.4 mm Hg (95% CI -1.3 to 0.4; p=0.3) per 10-year increase in age. Birthweight was not associated with diastolic blood pressure at any age. People from a manual social class in childhood had higher systolic and diastolic blood pressure than did those from a non-manual class. The effect on systolic blood pressure rose with age, by 1.0 mm Hg (95% CI 0.1 to 2.0; p=0.03) per 10 years, but was largely accounted for by current body-mass index, which was an increasingly strong determinant of blood pressure.

INTERPRETATION

These findings suggest that weight control throughout life is key to prevention of raised blood pressure during middle age. Understanding the link between the early childhood socioeconomic environment and adult obesity could make this strategy more effective.

Some aspects of the public health importance of measurement of growth

Growth is a fundamental process of life which in complex animals is influenced by genetic constitution, nurture and nutrition. Increase in size is accompanied by process of development and both growth and development are closely linked with time--the age of the individual. This paper considers ways in which simple measurements of different aspects of the growth of children have contributed, and are continuing to contribute, to our understanding of the origins of disease. The results of these measurements can help those involved in the care of children to identify individuals at risk of disturbances of growth and the possibility of the development of diseases associated with them. It can also help instigate preventative measures that may help children to develop more fruitful and longer disease-free lives.

Reduced endothelial vascular relaxation in growth-restricted offspring of pregnant rats with reduced uterine perfusion

Low birth weight as the result of placental insufficiency increases the risk of hypertension in young adults; however, the vascular mechanisms involved are unclear. We tested the hypothesis that intrauterine fetal growth restriction caused by placental insufficiency results in low-birth-weight offspring with impaired endothelium-dependent vascular relaxation, enhanced vasoconstriction, and hypertension. The body weight and arterial pressure were measured in young (4 weeks), adolescent (8 weeks), and adult (12 weeks) male offspring of normal pregnant rats and pregnant rats with reduced uteroplacental perfusion (intrauterine growth-restricted, IUGR), and aortic strips were isolated for measurement of isometric contraction. The body weight was lower whereas the arterial pressure was higher in IUGR than normal rats at 4 weeks (113+/-3 versus 98+/-2), 8 weeks (133+/-3 versus 121+/-6), and 12 weeks (144+/-4 versus 131+/-3 mm Hg). Phe (10(-5) mol/L) caused an increase in active stress that was greater in IUGR than in normal rats at 4 weeks (12.4 versus 7.8), 8 weeks (13.3 versus 8.4), and 12 weeks (14.6 versus 9.0x10(4) N/m2). Removal of the endothelium enhanced Phe-induced stress in normal but not IUGR rats. In endothelium-intact strips, acetylcholine (ACh) caused relaxation of Phe contraction and induced nitrite/nitrate production that were smaller in IUGR than normal rats. L-NAME (10(-4) mol/L), which inhibits NO synthase, or ODQ (10(-5) mol/L), which inhibits cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe contraction in normal but not IUGR rats. Thus endothelium-dependent NO-mediated vascular relaxation is inhibited in IUGR offspring of pregnant rats with reduced uteroplacental perfusion, and this may explain the increased vascular constriction and arterial pressure in young adults with low birth weight.

Prenatal exposure to nicotine modifies kidney weight and blood pressure in genetically susceptible rats: a case of gene-environment interaction

BACKGROUND

Epidemiologic studies suggest that in utero exposure to maternal smoking is associated with elevated blood pressure (BP) later in life. Our aims were: (1) to examine effects of intrauterine exposure to nicotine on BP and hypertension target-organ size in rats; and (2) to investigate whether such effects depend on genetic background, by studying two genetically distinct strains of rats: the spontaneously hypertensive rat (SHR) and the normotensive Brown Norway (BN) rat.

METHODS

Nicotine or saline was administered to dams via subcutaneous osmotic minipumps throughout gestation. In nine-week-old male offspring, we measured BP and heart rate, assessed the weight of kidneys and heart, and determined fasting levels of glucose, insulin, triglycerides (TG), and cholesterol. We also measured gene expression of the insulin-like growth factor (IGF) system in the liver and kidneys.

RESULTS

SHR and BN offspring differed in their response to intrauterine exposure to nicotine. SHR exposed to nicotine (vs. saline) exhibited higher BP (P < 0.02) and serum cholesterol levels (P = 0.01), and lower kidney weight (P < 0.0001). In contrast, BN rats did not demonstrate differences between the nicotine and saline groups in these variables, but the nicotine-exposed BN rats showed a significant up-regulation in the gene expression of IGF-1 in the liver (P < 0.0001) and IGF receptor in the kidney (P = 0.006).

CONCLUSION

These results suggest that intrauterine exposure to nicotine alters the cardiovascular system depending on the genetic background and, as such, supports the notion that the intrauterine environment interacts with genes in determining an individual's health later in life.

Social inequalities in low birth weight in England and Wales: trends and implications for future population health

STUDY OBJECTIVE

To examine social inequalities and trends in low birth weight in England and Wales.

DESIGN

Analysis of routine birth data, comparing (a) couple and sole registered births, and (b) manual and non-manual occupational groups.

SETTING

England and Wales, 1993-2000.

MAIN RESULTS

Social inequalities in low birth weight were evident throughout 1993-2000: relative to the non-manual group, there is an increased risk for the manual group (range in RR 1.22-1.35) and sole registrations (RR 1.51-1.67). An estimated 6.5% (2979 births) of low birth weight in 2000 could have been avoided if risks associated with the manual group were absent, and 2.8% (1290 births) avoided if risks associated with sole registration were absent. Between 1993 and 2000, the low birthweight rate increased significantly with an estimated overall increase of 11%. Increases were evident in all social groups (15% in manual, 11% in sole registrations and 9% in non-manual); however relative to non-manual the increase in RRs were not statistically significant for manual or sole registrations. When multiple births are excluded, the rate of low birth weight is reduced but there is still a significant increase over time and social differentials are undiminished.

CONCLUSIONS

There are social inequalities in low birth weight in England and Wales that have not narrowed over an eight year period, 1993-2000. These inequalities are likely to affect childhood and adult health inequalities in the future, hence strategies will need to address differences in low birth weight and further monitoring of trends is therefore desirable.

Low birth weight is associated with increased sympathetic activity: dependence on genetic factors

BACKGROUND

Low birth weight may be associated with high blood pressure in later life through genetic factors, an association that may be explained by alterations in sympathetic and parasympathetic activity. We examined the association of birth weight with cardiac pre-ejection period and respiratory sinus arrhythmia (indicators of cardiac sympathetic and parasympathetic activity, respectively) and with blood pressure in 53 dizygotic and 61 monozygotic adolescent twin pairs.

METHODS AND RESULTS

Birth weight of the twins was obtained from the mothers. Pre-ejection period and respiratory sinus arrhythmia were measured with electrocardiography and impedance cardiography at rest, during a reaction time task, and during a mental arithmetic task. In the overall sample, lower birth weight was significantly associated with shorter pre-ejection period at rest, during the reaction time task, and during the mental arithmetic task (P=0.0001, P<0.0001, and P=0.0001, respectively) and with larger pre-ejection period reactivity to the stress tasks (P=0.02 and P=0.06, respectively). In within-pair analyses, differences in birth weight were associated with differences in pre-ejection period at rest and during both stress tasks in dizygotic twin pairs (P=0.01, P=0.06, and P=0.2, respectively) but not in monozygotic twin pairs (P=0.9, P=1.0, and P=0.5, respectively). Shorter pre-ejection period explained approximately 63% to 84% of the birth weight and blood pressure relation.

CONCLUSIONS

Low birth weight is associated with increased sympathetic activity, and this explains a large part of the association between birth weight and blood pressure. In addition, our findings suggest that the association between birth weight and sympathetic activity depends on genetic factors.

Influence of chorionicity on the heritability estimates of blood pressure: a study in twins

BACKGROUND

A basic assumption of the twin design is that environmental influences including prenatal experiences are equal across twin types. However, the intra-uterine environment may differ according to the chorionicity of the monozygotic twins, which may have biased previous heritability estimates of blood pressure.

OBJECTIVE

The aim of the present study was to assess whether the heritability of blood pressure, derived from measurements in monozygotic and dizygotic twins, differs according to the chorionicity of the monozygotic twins.

METHODS

Conventional and 24-h ambulatory blood pressures were measured in 125 dizygotic twin pairs and in 97 dichorionic and 128 monochorionic monozygotic twin pairs at the age of 18-34 years. The twin sample was drawn from the East Flanders Prospective Twin Survey, in which perinatal data were collected at birth. Intra-pair correlation coefficients were calculated and compared between both types of monozygotic twin pairs. Heritability was estimated from model-fitting and path analysis, based on the dizygotic twins and, respectively, all monozygotic twins and the two subtypes.

RESULTS

Intra-pair correlation coefficients for the various blood pressures, after adjustment for body mass index, ranged from 0.45 to 0.71 in the monozygotic twin pairs and did not differ significantly according to chorionicity. Heritability estimates of blood pressure were between 52 and 64%, and were similar when calculated from dizygotic twins and, respectively, dichorionic and monochorionic monozygotic twins.

CONCLUSIONS

Heritability estimates of conventional and ambulatory blood pressure do not differ significantly according to the chorionicity of the monozygotic twins.

Growth velocity during the first postnatal week of life is linked to a spurt of IGF-I effect

There is adequate evidence that growth during the perinatal period is linked to the risk of several adult onset diseases, and recent findings indicate that the insulin-like growth factor (IGF) system is involved in prenatal growth, as reflected in birthweight. However, whether major components of the IGF system are involved in the immediate post-natal growth has not been studied. Maternal questionnaires were completed, and laboratory measurements of several variables, including IGF-I, IGF-II and IGF-binding protein-3 (IGFBP-3), were made for a total of 331 apparently healthy full-term newborns, from whom routine blood samples were taken during the first 5 days of their life. Birthweight and weight at the time of bleeding were among the recorded variables, and the difference divided by the age in days of the newborn was considered as reflecting immediate postnatal growth velocity. Immediate postnatal growth velocity was strongly positively associated with IGF-I. The squared adjusted correlation coefficient was 0.29 when IGF-I was incorporated in the model predicting postnatal growth velocity but was only 0.08 when IGF-I was excluded. In contrast, IGF-II and IGFBP-3 had no effect on postnatal growth velocity. It thus appears that IGF-I underlies growth during the immediate postnatal period. To the extent that perinatal growth may affect adult onset diseases, the findings of this study suggest that the action of IGF-I during the immediate postnatal period may represent a process of major importance.

Nutrition before birth, programming and the perpetuation of social inequalities in health

The need to explain social inequalities in health has led to the theory that chronic disease is due, in part, to a legacy of adverse experiences in early life. Epidemiological studies show consistently that individuals who are small at birth have an increased risk of cardiovascular disease in adulthood. There is growing consensus that this association reflects a causal relationship and is not simply the product of bias or confounding. The concept of programming is invoked as the biological mechanism; birth size is thus a proxy for fetal programming. Recent findings suggest that fetal programming interacts with the post-birth environment. The adverse exposures that are thought to underlie and potentiate programming cluster in socially patterned ways, thus creating substantial inequalities in health. Experiments in animals demonstrate that nutritional interventions before or during pregnancy can produce programming phenomena in the offspring, sometimes without an impact on birth size. However, the extent to which maternal nutrition contributes to programming in contemporary developed countries is uncertain.

Infant nutrition and blood pressure in early adulthood: the Barry Caerphilly Growth study

BACKGROUND

Evidence suggests that environmental factors acting early in life may affect blood pressure in adulthood.

OBJECTIVE

The objective was to test the hypothesis that dried formula milk (derived from cow milk) intake in infancy is positively associated with blood pressure in early adulthood.

DESIGN

We conducted a long-term follow-up (1997-1999) of the Barry Caerphilly Growth study cohort (1972-1974) into which mothers and their offspring had originally been randomly assigned to receive a milk supplement or usual care. Participants were the offspring, who were aged 23-27 y at follow-up. The main outcome measures were systolic and diastolic blood pressure.

RESULTS

The social and demographic characteristics of the subjects who were (n = 679) and were not (n = 272) followed up were similar. For each increase in quartile of dried milk consumption (in oz) at 3 mo of age, there was a 1.28-mm Hg (95% CI: 0.46, 2.10 mm Hg) increase in systolic and a 0.63-mm Hg (95% CI: 0.04, 1.22 mm Hg) increase in diastolic blood pressure after adjustment for sex, intervention group, birth weight z scores, social class in childhood, age at follow-up, alcohol consumption, and pack-years of smoking. These coefficients were attenuated when adult body mass index and height were included in the models, but the association of dried milk consumption at 3 mo of age with systolic pressure remained significant (1.07 mm Hg; 95% CI: 0.27, 1.87 mm Hg).

CONCLUSIONS

Our findings are consistent with the hypothesis that high blood pressure in later life is influenced by early postnatal nutrition. Thus, interventions to optimize infant nutrition may have important long-term health benefits.

Ethnicity modifies seasonal variations in birth weight and weight gain of infants

Early growth is considered critical for the development of obesity and adulthood cardiovascular diseases. Because season and environmental temperature at birth have also been associated with obesity, it is important to examine whether birth weight and postnatal weight gain vary by season. Data from the National Collaborative Perinatal Project were used to assess the influence of season on birth weight and weight gain during the first 4 mo of life. The sample included 11,091 whites, 11,477 blacks, 1536 Puerto Ricans and 221 subjects of other ethnic groups born at full-term gestation. Black infants born in the fall had a significantly lower birth weight (3.12 +/- 0.42 kg) than those born in the winter (3.16 +/- 0.43 kg, P = 0.002). This difference was not found in the other ethnic groups. Additionally, weight gain (g/mo) for black and Puerto Rican infants during the first 4 mo of life was significantly lower for those born during the fall (black: 816 +/- 186; Puerto Rican: 820 +/- 181) compared to those born in the spring (black: 844 +/- 194, P < 0.001) and summer (Puerto Rican: 861 +/- 185, P < 0.04). Birth weight and early infancy weight gain varied by season and were modified by ethnicity. The potential importance of seasonal variations in pre- and postnatal growth was evaluated in this study.

A role for suppressed thermogenesis favoring catch-up fat in the pathophysiology of catch-up growth

Catch-up growth is a risk factor for later obesity, type 2 diabetes, and cardiovascular diseases. We show here that after growth arrest by semistarvation, rats refed the same amount of a low-fat diet as controls show 1) lower energy expenditure due to diminished thermogenesis that favors accelerated fat deposition or catch-up fat and 2) normal glucose tolerance but higher plasma insulin after a glucose load at a time point when their body fat and plasma free fatty acids (FFAs) have not exceeded those of controls. Isocaloric refeeding on a high-fat diet resulted in even lower energy expenditure and thermogenesis and increased fat deposition and led to even higher plasma insulin and elevated plasma glucose after a glucose load. Stepwise regression analysis showed that plasma insulin and insulin-to-glucose ratio after the glucose load are predicted by variations in efficiency of energy use (i.e., in thermogenesis) rather than by the absolute amount of body fat or plasma FFAs. These studies suggest that suppression of thermogenesis per se may have a primary role in the development of hyperinsulinemia and insulin resistance during catch-up growth and underscore a role for suppressed thermogenesis directed specifically at catch-up fat in the link between catch-up growth and chronic metabolic diseases.

Birth weight and blood cholesterol level: a study in adolescents and systematic review

OBJECTIVE

To examine the relationship between birth weight and blood total cholesterol (TC) and to compare its strength with that of the relationship between current body mass index and TC.

METHODS

1). Cross-sectional study of adolescents, with retrospective ascertainment of birth weight from birth records or parental recall; 2). systematic review of studies examining the relations between birth weight and cholesterol at all ages.

PARTICIPANTS

1). 1532 individuals (92% white, 55% male) in 10 British towns; 2). 28 studies with 32 observations showing the change in TC per 1 kg increase in birth weight-6 in infancy, 14 in adolescents, 12 in adults.

RESULTS

In the cross-sectional study, there was a weak inverse relation between birth weight and TC level (-.061 mmol/L fall in TC per kg increase in birth weight, 95% confidence interval -.131 to.008 mmol/L per kg) which was little affected by adjustment for current body size. The difference in TC corresponding to an interquartile range increase in birth weight (-.03 mmol/L) was approximately a quarter of that for an equivalent increase in body mass index (.11 mmol/L). In the systematic review, an inverse association between birth weight and TC of a similar size to that in the cross-sectional study was observed (-.048 mmol/L per kg, 95% confidence interval -.078 to -.018 mmol/L per kg) similar in strength at all ages.

CONCLUSION

The relation of fetal nutrition to TC appears to be weak and is probably of limited public health importance when compared with the effects of childhood obesity.

Critical periods in human growth and their relationship to diseases of aging

It has long been recognized that there are "critical periods" during mammalian development when exposure to specific environmental stimuli are required in order to elicit the normal development of particular anatomical structures or their normal functioning. The responses of the organism to these stimuli depend on a specific level of anatomical maturation and a state of rapid anatomical and/or functional change. This discussion of critical periods in growth is not confined to the classic definition of a narrow time frame of development during which a particular environmental threshold or limit must exist for normal growth and function to ensue. Using both auxological and epidemiological approaches, we suggest a lifespan perspective which encompasses accumulating and interacting risks that are manifest from prenatal life onward. By understanding the process of growth development, and by scrutinizing the growth process, early variations that lead to later disease can be identified. Here we review a significant amount of the evidence that links exposure during growth to later morbidity and mortality. The fetus appears to respond to insults during the prenatal period through the process of "programming," which has short-term survival advantages but may have a long-term disadvantage in that it is associated with cardiovascular disease, hypertension, type II diabetes, and later obesity. Low birth weight combined with rapid postnatal growth during infancy also appears to be associated, for instance, with later childhood and adult sequelae in terms of glucose tolerance and obesity. Independent of birth weight, the timing of adiposity rebound during mid-childhood also predicts later obesity. The timing, magnitude, and duration of adolescent growth and maturationare associated with critical body composition changes, including the normal acquisition of body fat and bone mineralization. In particular, the acquisition of appropriate peak bone mass is critical in determining the later risk of osteoporosis. A putative causal mechanism linking early growth variation to later chronic disease risk through telomeric attrition is discussed. The obligatory loss of telomeric DNA with each cell division serves as a mitotic clock and marks the rate of growth and repair processes in the cell. Although much more work is required, existing studies support the notion that telomere shortening is not only a clock of cellular division, but also marks relative growth rate, as well as contributing to common degenerative processes of aging through its impact on cellular senescence.

Lipid profiles in adolescent Filipinos: relation to birth weight and maternal energy status during pregnancy

BACKGROUND

The finding that persons with low birth weight have a higher cardiovascular disease (CVD) risk than do persons with higher birth weight remains poorly understood.

OBJECTIVE

We tested the hypothesis that maternal arm fat area (MAFA) in the third trimester of pregnancy and birth weight of offspring are inversely related to the offspring's risk of CVD.

DESIGN

In a 1-y birth cohort study (1983-1984), 296 male and 307 female offspring were followed up (1998-1999) to measure their lipid profiles. Participants came from randomly selected communities of Cebu, Philippines.

RESULTS

MAFA (log cm2) was positively associated (beta) with HDL cholesterol (0.12 log mg/dL; P < 0.01) and inversely associated with total cholesterol (-10.0 mg/dL; P < 0.10), LDL cholesterol (-13.1 mg/dL; P < 0.01), and the ratios of total to HDL cholesterol and LDL to HDL cholesterol (both P < 0.001) in males. These relations were independent of birth weight, present adiposity, energy and fat intakes, maturity, and income. Birth weight < or = 2.6 kg was associated with elevated LDL cholesterol (9.9 mg/dL; P < 0.01) and an elevated ratio of LDL to HDL cholesterol (0.22; P < 0.10) only in males. In females, MAFA related positively to total (15.5 mg/dL; P < 0.05) and LDL (11.9 mg/dL; P < 0.05) cholesterol.

CONCLUSIONS

In this Filipino population, mothers with low energy status during pregnancy gave birth to male offspring who had a high CVD risk in adolescence, as indicated by lipid profiles. The findings in females are less consistent with the fetal origins hypothesis and suggest sex differences in the relation between fetal nutrition and postnatal lipid metabolism.

Birth weight impacts on wave reflections in children and adolescents

The objective of the present study was to assess central aortic pressure and wave reflection in children and adolescents at different birth weights. Two hundred nineteen healthy children (126 girls), from 7 to 18 years of age (mean, 11.3 years) and born at term after a normotensive pregnancy, were included. The subjects were divided according to birth weight: <2.5 kg, from 2.5 to 2.999 kg, from 3.0 to 3.5 kg, and >3.5 kg. Pressure waveforms were recorded from the radial artery of the wrist, and the waveform data were then processed by the SphygmoCor radial/aortic transform software module to produce the estimated aortic pressure waveform. Augmentation index, an estimate of the pulse wave reflection, was significantly higher in children with the lowest birth weights compared with the other birth weight groups. In a multiple regression analysis, short stature, low heart rate, female gender, and lower birth weight had independent significant inverse correlations to the augmentation index when adjusted for diastolic blood pressure (R2=0.21). In summary, the results showed a relatively aged phenotype of large-vessel function in the children with the lowest birth weights. These early alterations may be amplified throughout life and may contribute to the increased cardiovascular risk associated with low birth weight.

Low birth weight as a risk factor for hypertension

While the geographic and demographic disparities in the prevalence of hypertension have been recognized for decades, the reasons for these differences in disease risks remain unknown. The demographic and geographic patterns of hypertension are similar to those of low birth weight, giving support to the "Barker Hypothesis" which proposes a fetal origin of adult-onset disease. In fact, ecologic and observational studies throughout the world have detected significant associations of low birth weight and increased risks of hypertension. Nonetheless, the mechanisms for the association have not been fully described and documented. With some supportive evidence, proposed mechanisms include reduced nephrogenesis with a higher threshold for pressure natriuresis and greater susceptibility to progressive renal disease, impaired development of the endothelium, and increased sensitivity to glucocorticoids. Still, considerable work needs to be done to explain the birth weight/blood pressure relationship. The findings to date and the clinical significance warrant continued research in this intriguing area of study.

Kidney development and the fetal programming of adult disease

Recent evidence, from both epidemiological and animal experimental studies, suggest that the very first environment, the intrauterine, is extremely important in determining the future health of the individual. Genetic and 'lifestyle' factors impinge on, and can exacerbate, a 'programming' effect of an adverse fetal environment. In this review, we present compelling evidence to suggest that one of the major organs affected by an unfavourable prenatal environment is the kidney. Many of the factors that can affect fetal renal development (i.e. exposure to excess glucocorticoids, insufficient vitamin A, protein/calorie malnutrition (in rats) and alterations in the intrarenal renin angiotensinogen system), also produce hypertension in the adult animal. When nephron number is compromised during kidney development, maladaptive functional changes occur and can lead, eventually, to hypertension and/or renal disease. Surprisingly, it is during the very earliest stages of kidney development that the vulnerability to these effects occurs.

Placental insufficiency leads to development of hypertension in growth-restricted offspring

Low birth weight is a suggested risk factor for the development of hypertension. The purpose of the present study was to determine whether a model of intrauterine growth restriction produced in response to placental insufficiency in the pregnant rat was associated with marked elevations in blood pressure. Reduced uterine perfusion initiated in late gestation resulted in low-birth-weight offspring (5.8+/-0.1 versus 6.6+/-0.2 g, P<0.05, growth-restricted versus control, respectively). Mean arterial pressure, as measured in conscious, chronically instrumented rats, was significantly elevated as early as 4 weeks of age (113+/-3 versus 98+/-2 mm Hg, P<0.05) and was associated with significant decreases in body weight (66+/-2 versus 81+/-3 g, P<0.05) in growth-restricted (n=15) versus control (n=15) rats. Marked elevations in arterial pressure at 8 weeks of age (male: 133+/-3 versus 121+/-6 mm Hg, P<0.05; female: 137+/-4 versus 112+/-6 mm Hg, P<0.01) were associated with sex-specific decreases in body weight (male: 251+/-6 versus 275+/-10 g, P<0.05; female: 163+/-6 versus 180+/-6 g) in male growth-restricted (n=12) versus male control (n=9) rats and in female growth-restricted (n=8) versus female control (n=7) rats. At 12 weeks of age, hypertensive (144+/-4 versus 131+/-3 mm Hg, P<0.05) male growth-restricted offspring (n=10) had no alterations in glomerular filtration rate (2.3+/-0.3 versus 2.2+/-0.2 mL/min) compared with control (n=10) offspring; even when adjusted for kidney weight (1.7+/-0.3 versus 1.5+/-0.3 mL x min(-1) x g(-1) kidney), despite marked decreases in body weight (305+/-9 versus 343+/-10 g, P<0.05). These data suggest that placental insufficiency induced by reduced uterine perfusion in the pregnant rat results in low-birth-weight offspring predisposed to development of hypertension.

Rapid child growth raises blood pressure in adolescent boys who were thin at birth

Catch-up growth in previously growth-restricted children is a suggested risk factor for chronic disease risk. We use data from 2026 Filipino adolescents to identify periods of growth that matter more for risk of high blood pressure (BP). Subjects were drawn from the Cebu Longitudinal Health and Nutrition Survey, which enrolled pregnant women and followed up their offspring through age 14 to 16 years. High BP was defined as the top 10% of residuals from gender-specific regressions of systolic and diastolic BP on age and height. After controlling for birth length, current body mass index, age, and height, the odds of high BP in males were significantly decreased with each kilogram increase in birth weight. The highest odds of elevated BP occurred among males who were relatively thin at birth but relatively heavy as adolescents. Larger weight increments from birth to 2 years decreased the odds of high BP in boys, whereas larger increments from 8 to 11 and 11 to 16 years increased the odds of high BP. Thinness at birth significantly interacted with growth rate after age 8, such that a high rate of weight gain increased risk only among boys who were in the lower two thirds of the body mass index distribution at birth. Results in girls indicated small or no effects of early growth. The synergistic effect on adolescent BP of rapid weight gain from late childhood into adolescence with thinness at birth is further evidence of fetal programming of BP in males and suggests long-term health risks associated with rapid growth, even in the absence of obesity.

Self-perpetuating effects of birth size on blood pressure levels in elderly people

It has been suggested that essential hypertension is determined by 2 separate mechanisms: a growth-promoting process in childhood and a self-perpetuating mechanism in adult life. We report a clinical study of 500 people taken from a cohort of 7086 men and women who were born in Helsinki from 1924 to 1933, and whose body size at birth was recorded. As expected, blood pressure levels were inversely related to birthweight and birth length. These associations, however, were confined to the 213 people who had previously been diagnosed as having hypertension. In them, a 1-kg increase in birthweight was associated with a 6.4-mm Hg (95% confidence interval, 1.0 to 11.9) decrease in systolic blood pressure recorded at the clinic, and with a 9.3-mm Hg (95% confidence interval, 2.1 to 16.5) decrease recorded by ambulatory measurement. We conclude that pathological processes initiated in utero become self-perpetuating in adult life and lead to hypertension. Among elderly people with established hypertension, these processes have a strong effect on blood pressure levels, because they are processes that do not respond well to treatment.

Prenatal exposure to glucocorticoids and adult disease

There is evidence to suggest that an individual's susceptibility to cardiovascular disease cannot be entirely explained by differences in life style factors (i.e., low physical activity, high fat/salt diet), or genetic causes, but may also be influenced by factors encountered during intrauterine life. Epidemiological studies found the link between low birth weight for gestational age (a broad index of sub-optimal intrauterine environment) and increased incidence of cardiovascular and metabolic diseases in adulthood. Many animal models in which the intrauterine environment was altered during early/late or throughout gestation demonstrated long-term effects on adult health. In general stress in early gestation is more likely to be associated with adult cardiovascular disease including hypertension, whereas late gestation stress may also be associated with adult hypotension in addition to metabolic/endocrine abnormalities. Two systems have been widely hypothesised to serve as mechanisms via which adverse prenatal influences impinge on adult cardiovascular and metabolic disease; hippocampal-hypothalamo-pituitary-adrenal axis (HHPA) and renin-angiotensin system (RAS). Interestingly, at least in our animal model of adult hypertension after brief/early prenatal glucocorticoid exposure, HHPA axis is not altered when studied either in late gestation or at several stages during adulthood. However, our more recent results, using the same animal model, suggest a major role for the central and renal RAS. This review will mainly focus on animal models and potential mechanisms via which a perturbed intrauterine environment (undernutrition or steroid exposure) lead to adult cardiovascular and/or metabolic disease.

End-stage renal disease and acute glomerulonephritis in Goajiro Indians

BACKGROUND

Goajiro Indians are a semi-nomad tribe that live on the Goajiro peninsula, in the northwestern part of Venezuela. We investigated the incidence of end-stage renal disease (ESRD) and post-streptococcal glomerulonephritis (PSGN) among Goajiros and to determine if it was increased and whether congenital endowment of low number of nephrons (as indicated by low birth weight) was a contributing factor in their predisposition to chronic renal failure (CRF).

METHODS

The incidence of ESRD and the attack rate of poststreptococcal glomerulonephritis (PSGN) among Goajiros during the period December 1991 through December 1998 were evaluated from the records of the University Hospital, in Maracaibo, which is the referral center for Goajiro Indians. Demographic characteristics and birth weight were obtained from the records of the Regional Public Health Service. Subclinical reduction in renal functioning mass was investigated in 11 healthy Goajiros with a standardized tubular stress test that determines the increment in tubular secretion of creatinine (TSCr) resulting from the intravenous administration of a bolus of creatinine.

RESULTS

The incidence of ESRD among Goajiros was 220 patients per million inhabitants per year, 1.7 times higher than the incidence for the country. The attack rate of post-streptococcal glomerulonephritis is nearly double among Goajiro Indians (2.9 +/- 1.3 cases/100,000 inhabitants/year) than in the general population in the neighboring Maracaibo city (1.5 +/- 0.3, P < 0.02). Low weight birth was common among Goajiros; as many as 23% of newborns weigh less than 1000 g. The stimulated TSCr in healthy Goajiros was 30% lower than in controls (P < 0.001).

CONCLUSIONS

Goajiro Indians have a high incidence of ESRD. A high attack rate of PSGN and low nephron endowment in combination may be responsible, at least in part, for the increased risk of ESRD in this population.

Postnatal development of arterial pressure: influence of the intrauterine environment

A substantial number of epidemiological studies have shown that small size at birth is associated with an increased risk of developing hypertension and metabolic dysfunction later in life; however these associations have not been found in all studies. In animals, several models have been used to investigate the effects of perturbations to the fetal environment on later arterial pressure, with differing effects on size at birth and arterial pressure. Ovine models include maternal dietary manipulations, antenatal glucocorticoid exposure, and restriction of placental size and function. In our laboratory, we have induced late gestational placental insufficiency and growth restriction in sheep by umbilico-placental embolisation; during the early postnatal period the growth restricted lambs remained small and were hypotensive relative to controls. More recent long-term studies indicate that these growth restricted animals were able to catch up in body weight within the first postnatal year; however, their arterial pressure remained lower than that of controls throughout the first 2 postnatal years (deltaMAP, -4.2 +/- 1.4 mmHg). This relative hypotension may be due to altered vascular or cardiac development resulting from increased vascular resistance or nutrient restriction during fetal life. As late gestational placental insufficiency led to a persistent reduction in arterial pressure from birth to adulthood, our findings do not support the hypothesis that restricted fetal growth per se leads to hypertension after birth. It is likely that the effects of a prenatal compromise on postnatal arterial pressure will vary depending on the nature of the associated developmental perturbations and their gestational timing.

Blood pressure in late adolescence and very low birth weight

OBJECTIVES

To determine whether blood pressure (BP) differed between very low birth weight (VLBW; birth weight <or=1500 g) subjects and normal birth weight (NBW; birth weight >2499 g) subjects in late adolescence, and to determine whether growth restriction in utero was related to BP in VLBW survivors at this age.

METHODS

This was a cohort study of 210 preterm survivors with birth weights <1501 g born from January 1, 1977, to March 31, 1982, and 60 randomly selected NBW subjects from the Royal Women's Hospital, Melbourne. BP was measured at 18+ years of age in 156 (74%) VLBW subjects and 38 (63%) NBW subjects with both a standard mercury sphygmomanometer and an ambulatory BP monitor.

RESULTS

VLBW subjects had higher sphygmomanometer systolic and diastolic BPs than NBW subjects (mm Hg; mean difference [95% confidence interval]; systolic, 8.6 [3.4, 13.9]; diastolic, 4.3 [1.0, 7.6]). VLBW subjects also had significantly higher mean systolic ambulatory BPs (mm Hg; mean difference [95% confidence interval]) for the 24-hour period (4.7 [1.4, 8.0]), and for both the awake (5.0 [1.6, 8.5]) and asleep (3.6 [0.04, 7.1]) periods. There were no significant differences between the birth weight groups for any ambulatory diastolic BPs. Within the VLBW subjects, there was no significant relationship between birth weight standard deviation score and any measure of BP.

CONCLUSIONS

BP was significantly higher in late adolescence in VLBW survivors than in NBW subjects. Growth restriction in utero was not significantly related to BP in VLBW survivors.

Publication bias and heterogeneity in the relationship between systolic blood pressure, birth weight, and catch-up growth--a meta analysis

OBJECTIVE

To use meta-analytic techniques to formally examine (1) publication bias, and (2) between-study heterogeneity in the reported regression coefficient of systolic blood pressure (SBP) on birth weight, adjusting for current weight.

DATA IDENTIFICATION

A total of 55 separate analyses reporting on 382 514 male and female subjects ranging from 0 to 75 years, summarized in a recent systematic review.

RESULTS

Some 52 of 55 analyses reported a negative regression coefficient (beta) of SBP on birth weight, adjusting for current size, and in 27 of 55 (49%) the 95% confidence interval (CI) did not include zero. A pooled estimate of the regression coefficient across studies under a random-effects model was -1.38 mmHg/kg (95% CI: -1.66 to -1.10). The magnitude of the regression coefficient was negatively correlated with the age of the study population (r = -0.44, P = 0.0007). However, there was strong evidence of publication bias with smaller studies tending to report more negative betas - the Pearson correlation between beta and its standard error (SE(beta)) was -0.55 (P < 0.0001). To examine independent effects, meta analysis regressions of beta on age and SE(beta) were run. After controlling for age, there remained strong evidence of publication bias (P = 0.002), whereas after controlling for publication bias as measured by SE(beta), the relationship between beta and age was not significant (P = 0.08).

CONCLUSIONS

This analysis strongly suggests, but does not prove, that publication bias is present when systematically examining the relationship between blood pressure and birth weight. Controlling for publication bias lessens the apparent relationship between the regression coefficient and age of the study population.

Uising WinBUGS to fit nonlinear mixed models with an application to pharmacokinetic modelling of insulin response to glucose challenge in sheep exposed antenatally to glucocorticoids

Many chronic diseases of adulthood, such as hypertension and diabetes, are now believed to have at least some of their origins before birth. Extensive studies in animal models have identified antenatal exposure to excess glucocorticoids as a leading candidate for the physiological cause of fetal compromise. The resulting adverse intra-uterine environment appears to "program" the individual for higher risk of subsequent disease. We present an analysis of blood glucose and insulin concentrations collected during glucose tolerance tests at 6 and 12 months postnatal age in a cohort of sheep that were treated antenatally with injections of betamethasone (a synthetic glucocorticoid) which, when injected into the mother, cross the placenta to the fetus. A simple pharmacokinetic model, essentially a modification of the single compartment model with first-order absorption and elimination, is developed to describe the time course of glucose concentration and the associated insulin response. The resulting nonlinear mixed model is implemented in a Bayesian framework using the Markov chain Monte Carlo technique Gibbs Sampling via the software package BUGS. This sampling process allows inferences to be made directly about derived quantities with an immediate physical interpretation, such as the maximum insulin concentration in response to glucose challenge. At 6 months postnatal age, sheep treated with antenatal injections of synthetic glucocorticoids had raised insulin concentration in comparison to controls after bolus administration of glucose. This effect persisted to 12 months postnatal age only in the sheep that received multiple doses of glucocorticoids. Moreover, the raised insulin concentration in sheep that received direct injections of synthetic glucocorticoid as fetuses is accompanied by better glucose clearance than in those sheep that received only saline injections, a phenomenon that is not observed in the animals that received maternal injections. It is argued that the fitting of an appropriate statistical model to complex physiological data does not necessarily proclude a result that has a clear interpretation for clinical scientists.

Life course influences on insulin resistance: findings from the British Women's Heart and Health Study

OBJECTIVE

To assess the independent associations of a broad range of early life risk factors and adult obesity with adult insulin resistance.

RESEARCH DESIGN AND METHODS

This was a cross-sectional study of 1,394 women, aged 60-79 years, from 23 British towns.

RESULTS

There was a strong (independent of confounding factors, other early life factors, and adult waist-to-hip ratio) inverse association between birth weight and insulin resistance in women in the highest third of BMI (>28.77 kg/m2): -0.12 (95% CI -0.19 to -0.04) log homeostasis model assessment (HOMA) score per 1 SD birth weight, but no association between birth weight and insulin resistance in women in the two lowest thirds of BMI (P for interaction = 0.04). Offspring birth weight, own leg length, and childhood manual social class did not interact with adult obesity and were all independently inversely associated with insulin resistance: -0.05 (-0.09 to -0.01) log HOMA score per 1 SD offspring birth weight, -0.09 (-0.12 to -0.06) log HOMA score per 1 SD leg length, and a -0.07 (-0.14 to 0.00) difference in log HOMA score between manual and nonmanual childhood social class. Childhood manual social class and shorter leg length were both independently associated with adverse lipid profiles. BMI and waist-to-hip ratio were independently positively associated with insulin resistance and with all other components of the insulin resistance syndrome.

CONCLUSIONS

Insulin resistance is an important risk factor for type 2 diabetes and coronary heart disease. Our results suggest that genetic factors, intrauterine environment, early childhood, and adult environmental factors are all relevant in determining adult insulin resistance.

Relation of birth weight to fasting insulin, insulin resistance, and body size in adolescence

OBJECTIVE

A relationship between birth weight and the insulin resistance syndrome has been reported in adults but has not been defined in adolescents.

RESEARCH DESIGN AND METHODS

Data were analyzed in 296 children (132 girls and 164 boys) mean age 15.0 +/- 1.2 years who had euglycemic insulin clamp studies (intravenous administration of 1 mU. kg(-1). min(-1) of insulin balanced by a variable infusion of 20% glucose to maintain blood glucose at 100 mg/dl). Insulin sensitivity (M(LBM)) was determined by glucose uptake per kg lean body mass (LBM), and parents reported birth weight.

RESULTS

Birth weight ranged from 1,021 to 4,848 g (mean +/- SD 3,433 +/- 551), with 4.0% <2,500 g. Fat mass and BMI had U-shaped relations with birth weight after adjustment for race, age, sex, and blood pressure. Lean mass index (lean mass/height squared) was stable across birth weight quartiles. Fasting insulin decreased nonsignificantly across birth weight quartiles but became significant after adjustment for adolescent weight (P = 0.008). Although M(LBM) was highest in the highest birth weight quartile, the pattern was not significant. Triglycerides tended to increase with birth weight, whereas LDL cholesterol (LDL-C) and HDL cholesterol (HDL-C) tended to decrease. Blood pressure was unrelated to birth weight.

CONCLUSIONS

In this cohort, fat mass was greater in adolescents with low and high birth weight; fasting insulin was lower with higher birth weight after adjustment for adolescent weight. Insulin sensitivity increased nonsignificantly with birth weight.

Fetal origins of adult disease: strength of effects and biological basis

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 life-death, hospital treatment and the need for medication.

METHODS

Longitudinal study of 13 517 men and women who were born in Helsinki University Hospital during 1924-1944, 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 phenomena-developmental plasticity and compensatory growth.

Coronary heart disease: a disorder of growth

The search for the causes of CHD has been guided by a 'destructive' model, which proposes that influences acting in adult life, such as smoking, obesity or high saturated fat intakes, lead to an acceleration of age-related destructive processes, including a rise in blood pressure and the formation of atheroma. One explanation for the failure of the model to account for, or indeed to prevent rising epidemics of CHD, is that individuals are heterogeneous in their responses to such influences. This heterogeneity in response is linked to different paths of early growth. The recent discovery that individuals who develop CHD grew differently from other individuals during fetal life and in childhood has led to a new 'developmental' model for the disease. Reduced fetal growth followed by poor growth in infancy leads to an increased risk of development of CHD, and its associated conditions, stroke, hypertension and impaired glucose tolerance. These effects are compounded by accelerated weight gain, which may represent 'compensatory growth' in childhood.

Size at birth, gestational age and cortisol secretion in adult life: foetal programming of both hyper- and hypocortisolism?

OBJECTIVE

Recent studies have suggested that lifelong programming of the hypothalamic-pituitary-adrenal (HPA) axis in utero is an important mechanism in explaining the link between small size at birth and adult cardiovascular disease. However, direct evidence from human birth cohorts has so far been contradictory. We set out to study reasons for this discrepancy by examining the relationship between adult HPA axis function and birthweight and body proportions at birth in a group of elderly subjects with detailed birth records.

DESIGN

Birth cohort study.

SUBJECTS

Four hundred and twenty-one men and women (mean age 69.5 years, range 65.1-75.8 years) born at term in Helsinki, Finland, during 1924-33, with body size and gestational age at birth recorded.

MEASUREMENTS

Fasting serum cortisol and cortisol-binding globulin concentrations. The concentration of free cortisol was estimated by their ratio.

RESULTS

There was no significant correlation between fasting cortisol concentrations and birthweight in either men or women. However, there was a weak inverse association between fasting cortisol and length at birth in women but not in men. There was also a significant positive association between cortisol and ponderal index in both genders. We found that the association between foetal growth on fasting total and free cortisol concentrations differed in subjects born at different gestational ages. In subjects born before 39 weeks of gestation, both total and free cortisol showed inverse correlations with birthweight (P = 0.02 and P = 0.09, respectively) and length at birth (P = 0.001 and P = 0.02), whereas in subjects born after 40 weeks of gestation there were positive correlations with birthweight (P = 0.06 and P = 0.002) and ponderal index at birth (P = 0.003 and P = 0.003). The interactions between birthweight and gestational age were statistically significant (P = 0.01 for total and P = 0.003 for free cortisol).

CONCLUSIONS

These data suggest that the relationship between size at birth and cortisol concentrations in adult life is different in subjects born at different gestational ages: both hyper- and hypocortisolism may arise as a consequence of foetal programming of the hypothalamic-pituitary-adrenal axis during intrauterine life.

Programming effects of short prenatal exposure to dexamethasone in sheep

Recent studies have linked fetal exposure to a suboptimal intrauterine environment with adult hypertension. The aims of the present study were to see whether prenatal dexamethasone administered intravenously to the ewe between 26 to 28 days of gestation (1) resulted in high blood pressure in male and female offspring and whether hypertension in males was modulated by testosterone status, and (2) altered gene expression for angiotensinogen and angiotensin type 1 (AT1) receptors in the brain in late gestation and in the adult. Basal mean arterial pressure (MAP) at 2 years of age was significantly higher in wethers exposed to prenatal dexamethasone (group D; 106+/-5 mm Hg, n=9) compared with the control group (group S; 91+/-3 mm Hg, n=8; P<0.01). Infusion of testosterone for 3 weeks had no effect on MAP in either treatment group. At 130 days of gestation, dexamethasone administered between 26 to 28 days of gestation (group DF; n=8), resulted in an increased expression of angiotensinogen in hypothalamus (in arbitrary units: 2.5+/-0.3 versus 1.3+/-0.3 in the saline group [group SF], n=10; P<0.05). In addition, there was higher expression of the AT1 receptors in medulla oblongata in group DF (2.6+/-0.6 versus 1.1+/-0.2 in group SF; P<0.01). This effect of prenatal dexamethasone treatment was still evident in females at 7 years of age (group DA; n=5; 2.6+/-0.5 versus 1.1+/-0.2 in group SA; n=6, P<0.05). In conclusion, brief prenatal exposure of the pregnant ewe to dexamethasone leads to hypertension in adult animals of both sexes. Most interestingly, the mechanism leading to programming of hypertension might be linked with the brain angiotensin system.

Higher weight at birth is related to decreased maternal amino acid oxidation during pregnancy

BACKGROUND

Small size at birth is associated with cardiovascular disease in adult life. Decreased fetal growth may result from a limitation in the nutrient supply to the fetus. Net tissue deposition in the mother and fetus increases the demand for nitrogen, but because maternal consumption of protein does not increase, there must be a change in the partitioning of amino acids, away from oxidation and toward deposition.

OBJECTIVE

Our objective was to characterize amino acid oxidation in pregnancy and to investigate whether the relative partitioning of amino acids was related to fetal growth.

DESIGN

We determined amino acid oxidation as urea production in 25 women during mid (17-19 wk) and late (26-29 wk) gestation. Urea production was measured from urinary [(15)N-(15)N]urea excretion over 48 h after a single oral dose of [(15)N-(15)N]urea. We measured the infant's size at birth.

RESULTS

For the group as a whole, urea excretion decreased and amino acid oxidation remained similar between mid and late pregnancy, but there was wide variation between the women. Heavier infants were born to the mothers in whom amino acid oxidation decreased the most during pregnancy (slope of regression line: -80 g x g N(-1) x d(-1); 95% CI: -129, -31; P = 0.003). After adjustment for length of gestation and the infant's sex, the change in maternal amino acid oxidation explained 34% of the variation in birth weight.

CONCLUSIONS

Amino acid oxidation varied widely between the women during pregnancy. Understanding the ability of a pregnant woman to adapt metabolically may have implications for establishing dietary recommendations in pregnancy.

Birth weight rather than maternal nutrition influences glucose tolerance, blood pressure, and IGF-I levels in sheep

Both small size at birth in humans and maternal undernutrition in experimental animals are associated with impaired glucose tolerance and increased blood pressure in the adult offspring. However it is not clear whether maternal undernutrition in late gestation can influence postnatal phenotype, and whether this might occur independent of size at birth. We severely undernourished pregnant ewes for 10 d (UN10) or 20 d (UN20) from 105 d gestation (term = 146 d) and studied the offspring in comparison to those born to ad libitum fed ewes (AL20). Glucose tolerance tests and blood pressure recordings were performed at 5 mo of age and repeated at 30 mo together with insulin tolerance tests and GH challenges. UN20 lambs were lighter at birth (UN20, 4.9 +/- 0.1 kg, n = 23; UN10, 5.3 +/- 0.1 kg, n = 26; AL20, 5.6 +/- 0.2 kg, n = 26) but not from weaning onward. Plasma glucose area under the curve at 5 mo and plasma insulin at 30 mo increased with current weight and decreased with increasing birth weight. Blood pressure also increased with current weight and decreased with increasing birth weight at 5 but not 30 mo. Plasma IGF-I concentrations increased with current weight at all ages and decreased with increasing birth weight at 30 mo. Plasma insulin response to GH challenge increased with current weight. Nutrition group was not related to any of the outcomes measured when birth weight and current weight were taken into account. These data suggest that size at birth is more closely related to processes that determine postnatal phenotype than is maternal nutrition in late gestation.