Birthweight, adult risk factors and incident coronary heart disease: the Caerphilly Study

Leg length, insulin resistance, and coronary heart disease risk: the Caerphilly Study

BACKGROUND

Adult height has been inversely associated with coronary heart disease risk in several studies. The mechanism for this association is not well understood, however, and this was investigated by examining components of stature, cardiovascular disease risk factors and subsequent coronary heart disease in a prospective study.

METHODS

All men aged 45-59 years living in the town of Caerphilly, South Wales were approached, and 2512 (89%) responded and underwent a detailed examination, which included measurement of height and sitting height (from which an estimate of leg length was derived). Participants were followed up through repeat examinations and the cumulative incidence of coronary heart disease-both fatal and non-fatal-over a 15 year follow up period is the end point in this report.

RESULTS

Cross sectional associations between cardiovascular risk factors and components of stature (total height, leg length and trunk length) demonstrated that factors related to the insulin resistance syndrome-the homeostasis model assessment of insulin resistance, fasting triglyceride levels and total to HDL cholesterol ratio-were less favourable in men with shorter legs, while showing reverse or no associations with trunk length. Fibrinogen levels were inversely associated with leg length and showed a weaker association with trunk length. Forced expiratory volume in one second was unrelated to leg length but strongly positively associated to trunk length. Other risk factors showed little association with components of stature. The risk of coronary heart disease was inversely related to leg length but showed little association with trunk length.

CONCLUSION

Leg length is the component of stature related to insulin resistance and coronary heart disease risk. As leg length is unrelated to lung function measures it is unlikely that these can explain the association in this cohort. Factors that influence leg length in adulthood-including nutrition, other influences on growth in early life, genetic and epigenetic influences-merit further investigation in this regard. The reported associations suggest that pre-adult influences are important in the aetiology of coronary heart disease and insulin resistance.

Women's exposure to early and later life socioeconomic disadvantage and coronary heart disease risk: the Stockholm Female Coronary Risk Study

BACKGROUND

Measures of low socioeconomic position have been associated with increased risk for coronary heart disease (CHD) among women. A more complete understanding of this association is gained when socioeconomic position is conceptualized from a life course perspective where socioeconomic position is measured both in early and later life. We examined various life course socioeconomic indicators in relation to CHD risk among women.

METHODS

The Stockholm Female Coronary Risk Study is a population-based case-control study, in which 292 women with CHD aged < or =65 years and 292 age-matched controls were investigated using a wide range of socioeconomic, behavioural, psychosocial and physiological risk factors. Socioeconomic disadvantage in early life (large family size in childhood, being born last, low education), and in later life (housewife or blue-collar occupation at labour force entry, blue-collar occupation at examination, economic hardships prior to examination) was assessed.

RESULTS

Exposure to early (OR = 2.65, 95% CI : 1.12-6.54) or later (OR = 5.38, 95% CI : 2.01-11.43) life socioeconomic disadvantage was associated with increased CHD risk as compared to not being exposed. After simultaneous adjustment for marital status and traditional CHD risk factors, early and later socioeconomic disadvantage, exposure to three instances of socioeconomic disadvantage in early life was associated with an increased CHD risk of 2.48 (95% CI : 0.90-6.83) as compared to not being exposed to any disadvantage. The corresponding adjusted risk associated with exposure to later life disadvantage was 3.22 (95% CI : 1.02-10.53). Further analyses did not show statistical evidence of interaction effects between early and later life exposures (P = 0.12), although being exposed to both resulted in a 4.2-fold (95% CI : 1.4-12.1) increased CHD risk. Exposure to cumulative socioeconomic disadvantage (combining both early and later life), across all stages in the life course showed strong, graded associations with CHD risk after adjusting for traditional CHD risk factors. Stratification of cumulative disadvantage by body height showed that exposure to more than three periods of cumulative socioeconomic disadvantage had a 1.7- (95% CI : 0.9-3.2) and 1.9- (95% CI : 1.0-7.7) fold increased CHD risk for taller and shorter women, respectively. The combination of both short stature and more than two periods of cumulative socioeconomic disadvantage resulted in a 4.4-fold (95% CI : 1.7-9.3) increased CHD risk.

CONCLUSIONS

Both early and later exposure to socioeconomic disadvantage were associated with increased CHD risk in women. Later life exposure seems to be more harmful for women's cardiovascular health than early life exposure to socioeconomic disadvantage. However, being exposed to socioeconomic disadvantage in both early and later life magnified the risk for CHD in women. Cumulative exposure to socioeconomic disadvantage resulted in greater likelihood of CHD risk, even among women who were above median height. In terms of better understanding health inequalities among women, measures of socioeconomic disadvantage over the life course are both conceptually and empirically superior to using socioeconomic indicators from one point in time.

Early growth and coronary heart disease in later life: longitudinal study

OBJECTIVE

To determine how growth during infancy and childhood modifies the increased risk of coronary heart disease associated with small body size at birth.

DESIGN

Longitudinal study.

SETTING

Helsinki, Finland.

SUBJECTS

4630 men who were born in the Helsinki University Hospital during 1934-44 and who attended child welfare clinics in the city. Each man had on average 18.0 (SD 9.5) measurements of height and weight between birth and age 12 years.

MAIN OUTCOME MEASURES

Hospital admission or death from coronary heart disease.

RESULTS

Low birth weight and low ponderal index (birth weight/length(3)) were associated with increased risk of coronary heart disease. Low height, weight, and body mass index (weight/height(2)) at age 1 year also increased the risk. Hazard ratios fell progressively from 1.83 (95% confidence interval 1.28 to 2.60) in men whose body mass index at age 1 year was below 16 kg/m(2) to 1.00 in those whose body mass index was >19 (P for trend=0.0004). After age 1 year, rapid gain in weight and body mass index increased the risk of coronary heart disease. This effect was confined, however, to men with a ponderal index <26 at birth. In these men the hazard ratio associated with a one unit increase in standard deviation score for body mass index between ages 1 and 12 years was 1.27 (1.10 to 1.47; P=0.001).

CONCLUSION

Irrespective of size at birth, low weight gain during infancy is associated with increased risk of coronary heart disease. After age 1 year, rapid weight gain is associated with further increase in risk, but only among boys who were thin at birth. In these boys the adverse effects of rapid weight gain on later coronary heart disease are already apparent at age 3 years. Improvements in fetal, infant, and child growth could lead to substantial reductions in the incidence of coronary heart disease.

Hypothesis: pulse pressure and human longevity

In exploration of the association between pulse pressure and longevity in humans, 3 hypotheses are briefly discussed: the fetal origin hypothesis, antagonistic pleiotropy, and the telomere hypothesis of cellular aging. The implications of these hypotheses serve to draw a critical distinction between biologic age (aging) and chronological age and, thereby, offer an answer to a question that presently matters most in the field of hypertension: Why has it been so difficult to disentangle the genetic components of essential hypertension and to identify the variant genes responsible for elevated blood pressure in a large segment of the human population?

Fetal origins of adult disease: epidemiology and mechanisms

The past 10 years have provided unequivocal evidence that there are associations between birth size measures and future development of adult diseases, such as type 2 diabetes and coronary artery disease. Despite initial concern that bias or residual confounding in the analyses had produced these rather bizarre associations, the findings have now been reproduced in different cohorts by independent investigators from many parts of the world. The challenge for the next decade must be to discover the cellular and molecular mechanisms giving rise to these associations. If this aim is accomplished, it might be possible to devise strategies to reduce the impact of these disabling, chronic, and expensive diseases. The purpose of this review is to describe some of the relevant, important, and more recent epidemiological studies, and also to discuss potential mechanisms underpinning the associations.

Plasma lipid profiles in adults after prenatal exposure to the Dutch famine

BACKGROUND

Small body size at birth has been reported to be associated with an atherogenic lipid profile in humans, and animal experiments have shown that undernutrition during pregnancy permanently alters cholesterol metabolism in the offspring. There is no direct evidence in humans that maternal malnutrition during pregnancy affects the lipid profiles of the offspring.

OBJECTIVES

We assessed the effects of maternal malnutrition during specific periods of gestation on plasma lipid profiles in persons aged approximately 50 y.

DESIGN

This was a follow-up study of men and women born at term as singletons in a university hospital in Amsterdam between 1 November 1943 and 28 February 1947 around the time of a severe famine.

RESULTS

Persons exposed to famine in early gestation had a more atherogenic lipid profile than did those who were not exposed to famine in utero. Their LDL-HDL cholesterol ratios were significantly higher (by 13.9%; 95% CI: 2.6-26.4%). Additionally, their plasma HDL-cholesterol and apolipoprotein A concentrations tended to be lower, and their plasma total cholesterol, LDL-cholesterol, and apolipoprotein B concentrations tended to be higher, although these differences were not statistically significant. The effect of famine was independent of size at birth and adult obesity.

CONCLUSIONS

An atherogenic lipid profile might be linked to a transition from poor maternal nutrition in early gestation to adequate nutrition later on. This suggests that maternal malnutrition during early gestation may program lipid metabolism without affecting size at birth.

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

OBJECTIVE

To conduct a systematic review in order to (i) summarize the relationship between birthweight and blood pressure, following numerous publications in the last 3 years, (ii) assess whether other measures of size at birth are related to blood pressure, and (iii) study the role of postnatal catch-up growth in predicting blood pressure.

DATA IDENTIFICATION

All papers published between March 1996 and March 2000 that examined the relationship between birth weight and systolic blood pressure were identified and combined with the papers examined in a previous review.

SUBJECTS

More than 444,000 male and female subjects aged 0-84 years of all ages and races.

RESULTS

Eighty studies described the relationship of blood pressure with birth weight The majority of the studies in children, adolescents and adults reported that blood pressure fell with increasing birth weight, the size of the effect being approximately 2 mmHg/kg. Head circumference was the only other birth measurement to be most consistently associated with blood pressure, the magnitude of the association being a decrease in blood pressure by approximately 0.5 mmHg/cm. Skeletal and non-skeletal postnatal catch-up growth were positively associated with blood pressure, with the highest blood pressures occurring in individuals of low birth weight but high rates of growth subsequently.

CONCLUSIONS

Both birth weight and head circumference at birth are inversely related to systolic blood pressure. The relationship is present in adolescence but attenuated compared to both the pre- and post-adolescence periods. Accelerated postnatal growth is also associated with raised blood pressure.

Relationship of birth weight and length with growth in height and body diameters from 5 years of age to maturity

Birth weight and birth length were compared with several growth measures, including body height and weight, linear measures of limbs, body diameters, and head circumference, in 726 Melbourne schoolchildren of both sexes age 5-18 years. The analysis of relationships between three categories of birth length, weight, and growth measures were based on z-scores and performed by using analysis of variance and partial correlation. The data showed that birth length was correlated with body height and birth weight was correlated with head circumference; the relationships were weak and were less clear around the age corresponding to the peak height velocity in either sex. Further studies are needed to determine the common underlying mechanisms responsible for these associations. Am. J. Hum. Biol. 11:772-778, 1999. Copyright 1999 Wiley-Liss, Inc.

Potential mechanisms of metabolic imprinting that lead to chronic disease

This review synthesizes a subset of human epidemiologic and experimental animal studies that suggest that early nutrition affects susceptibility to chronic diseases in adulthood. These studies provide evidence that biological mechanisms may exist to "memorize" the metabolic effects of early nutritional environments. However, hypothesis-driven investigations of potential mechanisms have been scant. Thus, our understanding of the biology underlying metabolic imprinting is incomplete. A working definition of metabolic imprinting is proposed, emphasizing the adaptive nature and limited ontogenic window of the mechanisms putatively responsible for these relations. Five specific candidate mechanisms of metabolic imprinting are elaborated: 1) induced variations in organ structure, 2) alterations in cell number, 3) clonal selection, 4) metabolic differentiation, and 5) hepatocyte polyploidization. Last, experimental approaches for probing potential mechanisms with animal models are discussed.

Is the effect of low birth weight on cardiovascular mortality mediated through high blood pressure?

OBJECTIVE

To explore whether the inverse association between birth weight and mortality from circulatory diseases is mediated through blood pressure in men aged 50-75 years.

DESIGN

Cohort study with retrospectively collected data on size at birth.

SUBJECTS AND SETTING

The study included 1334 men born during 1920-1924, living in Uppsala, Sweden, who were examined at the ages of 50 and 60 years, and followed-up to the end of 1995.

MAIN OUTCOME MEASURES

Mortality from circulatory diseases based on routine death registration.

RESULTS

Birth weight showed a specific, inverse association with mortality from circulatory diseases: the rate ratio was 0.67 (95% confidence interval 0.50 to 0.89) per 1000 g increase in birth weight. This association was not appreciably affected by adjustment for sociodemographic characteristics or smoking, but was strengthened slightly by adjustment for body mass index at the ages of 50 and 60 years. Adjustment for systolic blood pressure at the age of 50 years only slightly reduced the strength of the inverse association between birth weight and mortality from ischaemic heart disease, and did not affect the inverse association between birth weight and mortality from stroke. Adjustments for systolic and diastolic blood pressure and hypertension treatment at the ages of 50 and 60 years did not reduce the strength of the association between birth weight and mortality from circulatory diseases at the age of 60-75 years.

CONCLUSIONS

The inverse association between birth weight and mortality from circulatory diseases in men aged 50-75 years is independent of adult sociodemographic characteristics, smoking and adult obesity and does not seem to be mediated through an increased blood pressure in those with low birth weight.

Reduced fetal growth rate and increased risk of death from ischaemic heart disease: cohort study of 15 000 Swedish men and women born 1915-29

OBJECTIVE

To establish whether fetal growth rate (as distinct from size at birth) is associated with mortality from ischaemic heart disease.

DESIGN

Cohort study based on uniquely detailed obstetric records with 97% follow up over the entire life course and linkage to census data in adult life.

SUBJECTS

All 14 611 babies delivered at the Uppsala Academic Hospital, Sweden, during 1915-29 followed up to end of 1995.

MAIN OUTCOME MEASURES

Mortality from ischaemic heart disease and other causes.

RESULTS

Cardiovascular disease showed an inverse association with birth weight for both men and women, although this was significant only for men. In men a 1000 g increase in birth weight was associated with a proportional reduction in the rate of ischaemic heart disease of 0.77 (95% confidence interval 0.67 to 0.90). Adjustment for socioeconomic circumstances at birth and in adult life led to slight attenuation of this effect. Relative to the lowest fourth of birth weight for gestational age, mortality from ischaemic heart disease in men in the second, third, and fourth fourths was 0.81 (0.66 to 0.98), 0.63 (0.50 to 0.78), and 0.67 (0.54 to 0.82), respectively. The inclusion of birth weight per se and birth weight for gestational age in the same model strengthened the association with birth weight for gestational age but removed the association with birth weight.

CONCLUSION

This study provides by far the most persuasive evidence of a real association between size at birth and mortality from ischaemic heart disease in men, which cannot be explained by methodological artefact or socioeconomic confounding. It strongly suggests that it is variation in fetal growth rate rather than size at birth that is aetiologically important.

Birthweight, body-mass index in middle age, and incident coronary heart disease

BACKGROUND

Several studies have shown a relation between fetal development, as shown by birthweight, and later coronary heart disease. This study investigated whether this relation is predominantly the consequence of early life exposures, or can best be explained in terms of an interaction between influences in early life and in adulthood.

METHODS

This prospective study in Caerphilly, South Wales, included 1258 men, aged 45-59 at initial screening, who were able to provide birthweight data. These men are from an initial cohort of 2512 men, from whom information has been obtained in a series of examinations since 1979 on health-related behaviours, incidence of coronary heart disease, and risk factors. The main outcome measure was fatal and non-fatal coronary heart disease during 10 years of follow-up.

FINDINGS

Higher birthweight was related to lower risk of coronary heart disease during the follow-up period: coronary heart disease occurred in 46 (11.6%) men in the lowest birthweight tertile, 44 (12.0%) of those in the middle tertile, and 38 (9.1%) of those in the highest tertile (p = 0.03). Stratification of the cohort by body-mass index (BMI) revealed a significant interaction such that the inverse association between birthweight and risk of coronary heart disease was restricted to men in the top tertile of BMI (interaction test p = 0.048 adjusted for age, and p = 0.012 fully adjusted). Within the top BMI tertile, coronary heart disease occurred in 19 (16.4%) of men in the lowest birthweight tertile, 13 (12.6%) of those in the middle tertile, and 13 (7.5%) of those in the highest tertile (p = 0.0005). These associations were not changed substantially by adjustment for age, father's social class, own social class, marital status, fibrinogen and cholesterol concentrations, systolic blood pressure, and smoking history.

INTERPRETATION

The association between birthweight and risk of coronary heart disease cannot be explained by associations with childhood or adulthood socioeconomic status. Nor do conventional risk factors for coronary heart disease in adulthood account for the association. However, there is an important interaction between birthweight and BMI such that the increased risk of coronary heart disease associated with low birthweight is restricted to people who have high BMI in adulthood. Risk of coronary heart disease seems to be defined by the combined effect of early-life and later-life exposures.