Statistical issues in life course epidemiology

Late midlife C-reactive protein and interleukin-6 in middle aged danish men in relation to body size history within and across generations

OBJECTIVE

The aim was to estimate the effects of ponderal index at birth and body mass index (BMI) in early adulthood on C-reactive protein (CRP) and interleukin-6 (IL-6) and to quantify the effects through subsequent measures of body size. In a subanalysis, the contributions of maternal BMI to the inflammatory status of offspring were investigated.

METHODS

The study was based on 2,986 Danish males from the Copenhagen Aging and Midlife Biobank. Path analysis was employed to estimate direct and indirect effects.

RESULTS

A 10% higher maternal BMI was associated with 7% higher CRP and 3% higher IL-6 among offspring. A 10% higher ponderal index at birth was associated with 4% lower CRP in late midlife; this effect was only partially mediated by later growth. A 10% higher BMI in early adulthood was associated with 8% higher CRP and 4% higher IL-6 in late midlife. The findings suggest that weight gain in adulthood is associated with low-grade inflammation in late midlife.

CONCLUSIONS

Ponderal index at birth is associated with CRP in later life independently of adult BMI. The findings additionally suggest that preventing weight gain in early adulthood would be beneficial for inflammatory status in later life.

Quantifying risk over the life course - latency, age-related susceptibility, and other time-varying exposure metrics

Identification of the latency period and age-related susceptibility, if any, is an important aspect of assessing risks of environmental, nutritional, and occupational exposures. We consider estimation and inference for latency and age-related susceptibility in relative risk and excess risk models. We focus on likelihood-based methods for point and interval estimation of the latency period and age-related windows of susceptibility coupled with several commonly considered exposure metrics. The method is illustrated in a study of the timing of the effects of constituents of air pollution on mortality in the Nurses' Health Study. Copyright © 2016 John Wiley & Sons, Ltd.

Does childhood bullying predict eating disorder symptoms? A prospective, longitudinal analysis

OBJECTIVE

Bullying is a common childhood experience with enduring psychosocial consequences. The aim of this study was to test whether bullying increases risk for eating disorder symptoms.

METHOD

Ten waves of data on 1,420 participants between ages 9 and 25 were used from the prospective population-based Great Smoky Mountains Study. Structured interviews were used to assess bullying involvement and symptoms of anorexia nervosa and bulimia nervosa as well as associated features. Bullying involvement was categorized as not involved, bully only, victim only, or both bully and victim (bully-victims).

RESULTS

Within childhood/adolescence, victims of bullying were at increased risk for symptoms of anorexia nervosa and bulimia nervosa as well as associated features. These associations persisted after accounting for prior eating disorder symptom status as well as preexisting psychiatric status and family adversities. Bullies were at increased risk of symptoms of bulimia and associated features of eating disorders, and bully-victims had higher levels of anorexia symptoms. In terms of individual items, victims were at risk for binge eating, and bully-victims had more binge eating and use of vomiting as a compensatory behavior. There was little evidence in this sample that these effects differed by sex. Childhood bullying status was not associated with increased risk for persistent eating disorder symptoms into adulthood (ages 19, 21, and 25).

DISCUSSION

Bullying predicts eating disorder symptoms for both bullies and victims. Bullying involvement should be a part of risk assessment and treatment planning for children with eating problems.

Impact of blood pressure on retinal microvasculature architecture across the lifespan: the Young Finns Study

OBJECTIVE

The present study examined the impact of BP from childhood to mid-adulthood on retinal microvascular architecture.

METHODS

The Cardiovascular Risk in Young Finns Study included children aged 3-18 years, from five Finnish University cities, with participants chosen randomly from the national population registrar from those areas. The age of participants included in the current analyses in childhood (1980) ranged from three to nine years and in mid-adulthood (2011) ranged from 34 to 40 years (complete data n = 657). Measures of retinal microvasculature architecture measured in adulthood included diameters, tortuosity, lengths, and LDR.

RESULTS

Regression analysis showed a strong negative association between childhood systolic BP and adult arteriolar diameter (standardized regression coefficient [β] -0.300; p < 0.001) and with change in systolic BP from childhood to adulthood (β = -0.249; p < 0.001). For arteriolar tortuosity, there was a strong positive association between childhood systolic BP and adult arteriolar tortuosity (β = 0.154; p < 0.001) and no association with change in systolic BP from childhood to adulthood (β = 0.072; p = 0.110).

CONCLUSIONS

High BP in childhood and increased BP from childhood to adulthood impacts on retinal microvascular architecture in mid-adulthood.

Are Early-Life Socioeconomic Conditions Directly Related to Birth Outcomes? Grandmaternal Education, Grandchild Birth Weight, and Associated Bias Analyses

Grandmaternal education may be related to grandchild birth weight (GBW) through maternal early-life development; however, conventional regression models may be endogenously confounded. Alternative models employing explicit structural assumptions may provide incrementally clearer evidence. We used data from the US National Longitudinal Study of Adolescent to Adult Health (1995-2009; 1,681 mother-child pairs) to estimate "direct effects" of grandmaternal educational level (less than high school, high school diploma or equivalent, or college degree) at the time of the mother's birth on GBW, adjusted for maternal life-course factors: maltreatment as a child, education and income as an adult, prepregnancy overweight, and prenatal smoking. Using conventional and marginal structural model (MSM) approaches, we estimated 54-g (95% confidence interval: -14.0, 122.1) and 87-g (95% confidence interval: 10.9, 162.5) higher GBWs per increase in educational level, respectively. The MSM allowed simultaneous mediation by and adjustment for prepregnancy overweight. Estimates were insensitive to alternate structural assumptions and mediator parameterizations. Bias analysis suggested that a single unmeasured confounder would have to have a strong influence on GBW (approximately 150 g) or be greatly imbalanced across exposure groups (approximately 25%) to completely explain the findings. Coupling an MSM with sensitivity analyses provides some evidence that maternal early-life socioeconomic environment is directly associated with offspring birth weight.

A life course approach to cardiovascular aging

A life course approach in epidemiology investigates the biological, behavioral and social pathways that link physical and social exposures and experiences during gestation, childhood, adolescence and adult life, and across generations, to later-life health and disease risk. We illustrate how a life course approach has been applied to cardiovascular disease, highlighting the evidence in support of the early origins of disease risk. We summarize how trajectories of cardiometabolic risk factors change over the life course and suggest that understanding underlying 'normal' or 'healthy' trajectories and the characteristics that drive deviations from such trajectories offer the potential for early prevention and for identifying means of preventing future disease.

Satisfaction with dental care and life-course predictors: A 20-year prospective study of a Swedish 1942 birth cohort?

OBJECTIVES

The aim was to assess the impact of care experience, health factors and socioeconomic factors on satisfaction with dental care across time and to assess the stability or change in levels of self-reported satisfaction with dental care in individuals as they progress from middle age to early old age.

MATERIALS AND METHODS

The present work is based on five separate data collections from a cohort study with 3585 individuals responding in all years of the survey. Data collection was conducted in 1992 when the subjects were 50 years of age and again 5, 10, 15 and 20 years later. Absolute stability in satisfaction with dental care was assessed by calculating the proportion of individuals who maintained their position in the same category from one survey period to another. Changes across time were tested using Cochran's Q test. Satisfaction with dental care across the 20-year survey period was modeled using the generalized estimating equation (GEE).

RESULTS AND CONCLUSION

The result showed that 85% of women and 83% of men remained satisfied with dental care. Binomial GEE revealed no statistical significant change in satisfaction with dental care between 1992-2012. In sum, this study has shown that this age group, born in 1942, was stably satisfied with dental care between age 50 and age 70, despite all changes during this time period. Females are more satisfied than men and the most important factors are the experience of attention during the last visit, satisfaction with dental appearance and good chewing capability.

Life-course body mass index trajectories and blood pressure in mid life in two British birth cohorts: stronger associations in the later-born generation

Background: Little is known about the impact of recent increases in obesity and more rapid gains in body mass index (BMI) on cardiovascular risk factors. We investigated life-course BMI trajectories associations with adult blood pressure (BP) across two generations.

Methods: We used the the 1946 and 1958 British birth cohorts. Joint multivariate response models were fitted to longitudinal BMI measures [7, 11, 16, 20, 26, 36, 43 and 50 y (years): 1946 cohort, n = 4787; 7, 11, 16, 23, 33 and 45 y: 1958 cohort, n = 16 820] and mid-adult BP. We adopted linear spline models with random coefficients to characterize childhood and adult BMI slopes.

Results: Mean systolic BP (SBP) decreased from the earlier- to later-born cohort by 2.8 mmHg in females, not males; mean diastolic BP (DBP) decreased by 3.2-3.3 mmHg (both sexes). Adult BMI was higher in the later- than the earlier-born cohort by 1.3-1.8 kg/m², slopes of BMI trajectory were steeper from early adulthood and associations with adult BP were stronger. Associations between adult BMI and SBP were stronger in the later-born cohort. For males, childhood BMI slope was associated with SBP only in the later-born cohort; the association for adult BMI slope was stronger in the later-born cohort: correlation coefficient r = 0.28 [95% confidence interval (CI): 0.25,0.33] versus 0.13 (0.06,0.20). For females, childhood slope was associated with SBP in both cohorts; adult slope was associated with SBP only in the 1958 cohort [r = 0.34 (0.31,0.37)]. Patterns of child-to-adult BMI associations were similar in relation to DBP.

Conclusions: BP did not increase between two generations born 12 y apart despite higher BMI levels. A stronger association between BMI trajectory and BP in the later-born cohort suggests that BMI-related effects may have been offset by improvements in other factors linked to BP, such as diet and smoking.

Meta-Analytic Approaches for Multistressor Dose-Response Function Development: Strengths, Limitations, and Case Studies

For many policy analyses, including but not limited to cumulative risk assessments, it is important to characterize the individual and joint health effects of multiple stressors. With an increasing focus on psychosocial and other nonchemical stressors, this often includes epidemiological meta-analysis. Meta-analysis has limitations if epidemiological studies do not include all of the stressors of interest or do not provide multivariable outputs in a format necessary for risk assessment. Given these limitations, novel analytical methods are often needed to synthesize the published literature or to build upon available evidence. In this article, we discuss three recent case studies that highlight the strengths and limitations of meta-analytic approaches and other research synthesis techniques for human health risk assessment applications. First, a literature-based meta-analysis within a risk assessment context informed the design of a new epidemiological investigation of the differential toxicity of fine particulate matter constituents. Second, a literature synthesis for an effects-based cumulative risk assessment of hypertension risk factors led to a decision to develop new epidemiological associations using structural equation modeling. Third, discrete event simulation modeling was used to simulate the impact of changes in the built environment on environmental exposures and associated asthma outcomes, linking literature meta-analyses for key associations with a simulation model to synthesize all of the model components. These case studies emphasize the importance of conducting epidemiology with a risk assessment application in mind, the need for interdisciplinary collaboration, and the value of advanced analytical methods to synthesize epidemiological and other evidence for risk assessment applications.

Life course models for upper aero-digestive tract cancer

Upper aero-digestive tract (UADT) cancers are collectively cancers of various human body sites, such as the oral cavity, pharynx, oesophagus and larynx. Worldwide, they are the fourth most frequent cancer type and the fourth most common cause of mortality from cancer. Many studies have shown that several chronic diseases, such as cancer, which occur more commonly in later adulthood, are influenced by social and psychological circumstances during birth, childhood, adolescence and early adult life. It is suggested that the build up of problematic circumstances throughout life is the cause of disease, rather than circumstances that happen at one point in time. UADT cancer is a chronic disease of complex multifactorial origin and most of the underlying exposures/risks cannot be considered as individual factors or in isolation, as they act at different levels, which differ from time to time. Thus, life-course epidemiology, rather than drawing false dichotomies between different risk factors of the underlying disease, attempts to integrate biological and social risk processes that cause the chronic disease. It studies how socially patterned exposures during all stages of life--childhood, adolescence and early adult--influence disease risk in adulthood and socio-economic position and hence may account for social inequalities in adult health and mortality. Furthermore, varying health effects, according to the timing or duration of exposure to socio-economic circumstances, may indicate important traces to the causes of cancer. In this paper, we have attempted to draw a conceptual framework on the relationships between socio-economic inequalities, oral health risk factors along the life-course of an individual and incidence of UADT cancer.

Analytical strategies in human growth research

Human growth research requires knowledge of longitudinal statistical methods that can be analytically challenging. Even the assessment of growth between two ages is not as simple as subtracting the first measurement from the second, for example. This article provides an overview of the key analytical strategies available to human biologists in increasing order of complexity, starting with a review on how to express cross-sectional measurements of size, before covering growth (conditional regression models, regression with conditional growth measures), growth curves (individual growth curves, mixed effects growth curves, latent growth curves), and patterns of growth (growth mixture modeling). The article is not a statistical treatise and has been written by a human biologist for human biologists; as such, it should be accessible to anyone with training in at least basic statistics. A summary table linking each analytical strategy to its applications is provided to help investigators match their hypotheses and measurement schedules to an analysis plan. In addition, worked examples using data on non-Hispanic white participants in the Fels Longitudinal Study are used to illustrate how the analytical strategies might be applied to gain novel insight into human growth and its determinants and consequences. All too often, serial measurements are treated as cross-sectional in analyses that do not harness the power of longitudinal data. The broad goal of this article is to encourage the rigorous application of longitudinal statistical methods to human growth research.

The contribution of childhood cardiorespiratory fitness and adiposity to inflammation in young adults

OBJECTIVE

Cardiorespiratory fitness and adiposity may influence cardiovascular risk through their effects on inflammation. The long-term effects of these modifiable factors on adult inflammation remain uncertain. The associations of childhood and adulthood cardiorespiratory fitness and adiposity with adult inflammation [C-reactive protein (CRP), fibrinogen] were examined.

METHODS

1,976 children examined in 1985 and re-examined as young adults in 2004-2006 were included. Cardiorespiratory fitness and adiposity were assessed at both waves. CRP and fibrinogen were measured at follow-up.

RESULTS

Higher childhood fitness was associated with lower adult inflammation in both sexes. After adjusting for childhood adiposity, the association with CRP attenuated in males, but remained in females (average reduction of CRP 18.1% (95% CI 11.3-24.4%) per 1-SD increase in childhood fitness). Higher adult fitness, adjusting for childhood fitness (an increase in fitness from childhood to adulthood), was associated with lower adult CRP in females and lower fibrinogen in males. Higher childhood and adulthood adiposity (an increase in adiposity from childhood to adulthood) were associated with higher adult inflammation in both sexes.

CONCLUSIONS

Prevention programs to increase fitness and reduce adiposity in childhood, and maintain a favorable fitness and weight into adulthood, may lead to reduction in adult systemic inflammation.

Modelling childhood growth using fractional polynomials and linear splines

BACKGROUND

There is increasing emphasis in medical research on modelling growth across the life course and identifying factors associated with growth. Here, we demonstrate multilevel models for childhood growth either as a smooth function (using fractional polynomials) or a set of connected linear phases (using linear splines).

METHODS

We related parental social class to height from birth to 10 years of age in 5,588 girls from the Avon Longitudinal Study of Parents and Children (ALSPAC). Multilevel fractional polynomial modelling identified the best-fitting model as being of degree 2 with powers of the square root of age, and the square root of age multiplied by the log of age. The multilevel linear spline model identified knot points at 3, 12 and 36 months of age.

RESULTS

Both the fractional polynomial and linear spline models show an initially fast rate of growth, which slowed over time. Both models also showed that there was a disparity in length between manual and non-manual social class infants at birth, which decreased in magnitude until approximately 1 year of age and then increased.

CONCLUSIONS

Multilevel fractional polynomials give a more realistic smooth function, and linear spline models are easily interpretable. Each can be used to summarise individual growth trajectories and their relationships with individual-level exposures.

Impact of adiposity on cardiac structure in adult life: the Childhood Determinants of Adult Health (CDAH) study

BACKGROUND

We have examined the association between adiposity and cardiac structure in adulthood, using a life course approach that takes account of the contribution of adiposity in both childhood and adulthood.

METHODS

The Childhood Determinants of Adult Health study (CDAH) is a follow-up study of 8,498 children who participated in the 1985 Australian Schools Health and Fitness Survey (ASHFS). The CDAH follow-up study included 2,410 participants who attended a clinic examination. Of these, 181 underwent cardiac imaging and provided complete data. The measures were taken once when the children were aged 9 to 15 years, and once in adult life, aged 26 to 36 years.

RESULTS

There was a positive association between adult left ventricular mass (LVM) and childhood body mass index (BMI) in males (regression coefficient (β) 0.41; 95% confidence interval (CI): 0.14 to 0.67; p = 0.003), and females (β = 0.53; 95% CI: 0.34 to 0.72; p < 0.001), and with change in BMI from childhood to adulthood (males: β = 0.27; 95% CI: 0.04 to 0.51; p < 0.001, females: β = 0.39; 95% CI: 0.20 to 0.58; p < 0.001), after adjustment for confounding factors (age, fitness, triglyceride levels and total cholesterol in adulthood). After further adjustment for known potential mediating factors (systolic BP and fasting plasma glucose in adulthood) the relationship of LVM with childhood BMI (males: β = 0.45; 95% CI: 0.19 to 0.71; p = 0.001, females: β = 0.49; 95% CI: 0.29 to 0.68; p < 0.001) and change in BMI (males: β = 0.26; 95% CI: 0.04 to 0.49; p = 0.02, females: β = 0.40; 95% CI: 0.20 to 0.59; p < 0.001) did not change markedly.

CONCLUSIONS

Adiposity and increased adiposity from childhood to adulthood appear to have a detrimental effect on cardiac structure.

Cardiovascular Risk Factors from Early Life Predict Future Adult Cardiac Structural and Functional Abnormalities: A Systematic Review of the Published Literature

Background

Clinical practice evaluates cardiovascular risk based on current risk factor (RF) levels [Blood pressure (BP), body mass index (BMI) and glycaemic control] largely disregarding previous risk-factor history over the totality of the life course. RFs are related to contemporaneous echocardiographic measures of cardiac structure and function which in turn are independently related to cardiovascular morbidity and mortality in cross-sectional studies. However, the effect of lifetime or earlier RF history on future echocardiographic changes has never been systematically examined.

Methods

A systematic review of the published literature identified 24 studies relating either earlier BP, BMI, glycaemic control or a combination to future cardiac structure and/or function.

Results

The majority of studies showed that elevated BP and BMI in earlier life and greater cumulative burden of these factors resulted in worse cardiac structure up to 24 years later. Studies examining glycaemic control as RF were few, but poorer glycaemic control in young adults was associated with increased future left ventricular mass.

While only 5 papers related RFs to future cardiac function, all RFs were positively associated with worse future diastolic function.

Conclusions

BP, BMI and glycaemic control measures in childhood, adolescence and early adulthood and subsequent longitudinal trajectories of BP and BMI are predictive of future abnormalities in cardiac structure and function. Lifetime RF history should be used to inform clinical practice. Further research is required to enable the identification of any sensitive periods in the life course to enable prevention when it is most likely to be effective.

Are the educational differences in incidence of cardiovascular disease explained by underlying familial factors? A twin study

To isolate the effect of education from the influence of potential underlying factors, we investigated the association of education with the risk of cardiovascular disease (CVD) and ischemic heart disease (IHD) using twin data to adjust for familial factors shared within twins, including genetic make-up and childhood environment. The study was based on data from the Danish Twin Registry linked to administrative and heath registers in Statistics Denmark. A total of 11,968 monozygotic and 20,464 dizygotic same sexed twins were followed from 1980 to 2009, including more than 8000 events of CVD. Unpaired and intra-pair analyses were compared. In the unpaired analyses, an inverse educational gradient in CVD- and IHD risk was observed. This association was not replicated in the intra-pair analyses that control for shared familial factors exploiting that twins share their intrauterine- and childhood environment and are matched partly or fully on genetic setup. The attenuation of association of education with CVD and IHD in the intra-pair analyses suggests that shared familial factors account for a substantial part of the observed association of education with CVD and IHD in Denmark.

Intergenerational determinants of offspring size at birth: a life course and graphical analysis using the Aberdeen Children of the 1950s Study (ACONF)

BACKGROUND

Size at birth has taken on renewed significance due to its now well-established association with many health and health-related outcomes in both the immediate perinatal period and across the entire life course. Optimizing fetal growth to improve both neonatal survival and population health is the focus of much research and policy development, although most efforts have concentrated on either the period of pregnancy itself or the period immediately preceding it.

METHODS

Intergenerational data linked to the Aberdeen Children of the 1950s (ACONF) study were used to examine the influence of grandparental and parental life course biological and social variables on the distribution of offspring size at birth. Guided stepwise multivariable methods and a graphical approach were used to assess the relative importance of these temporally ordered and highly correlated life course measures.

RESULTS

Both distal and proximal grandparental and parental life course biological and social factors predicted offspring size at birth. Inequalities in size at birth, according to adult maternal socioeconomic indicators, were found to be largely generated by the continuity of the social environment across generations, and the inequalities in maternal early life growth were predicted by the adult grandparental social environment during the mother's early life. Mother's own size at birth predicted her offspring's intrauterine growth, independent of her adult biological and social characteristics.

CONCLUSIONS

A mother's childhood social environment and her early growth are both important predictors of her offspring's size at birth. Population strategies aimed at optimizing size at birth require broader social and intergenerational considerations, in addition to focusing on the health of mothers in the immediate pregnancy period.

How do pregnancy-related weight changes and breastfeeding relate to maternal weight and BMI-adjusted waist circumference 7 y after delivery? Results from a path analysis

BACKGROUND

Reproduction has been related to long-term maternal weight gain, and changes in fat mass, with gestational weight gain, have been identified as an important contributor. However, the influence of weight changes during the whole reproductive cycle and the modifying effect of breastfeeding are unknown.

OBJECTIVE

The objective was to examine how prepregnancy weight, gestational weight gain, postpartum weight changes, and breastfeeding influence maternal weight and body mass index-adjusted waist circumference (WCBMI) 7 y after delivery.

DESIGN

This was a prospective cohort study of 23,701 women participating in the Danish National Birth Cohort with singleton births and no births during follow-up. Path analysis was used to assess the total, direct, and indirect effects; the latter was mediated through weight changes on the pathways.

RESULTS

Postpartum weight retention at 6 mo and weight gain from 6 to 18 mo postpartum were highly positively associated with both outcomes. A 1-kg increase in weight retention at 6 mo postpartum corresponded to an average increase of 0.5 kg at 7 y. Gestational weight gain was not associated with WCBMI but was positively associated with weight at 7 y; 87% of this effect was mediated through later weight changes. For both outcomes, a small inverse association was observed for breastfeeding duration. This was strongest for WCBMI, for which 97% of the effect was direct, ie, not mediated through postpartum weight.

CONCLUSIONS

These findings show that postpartum weight retention at 6 mo and weight gain from 6 to 18 mo postpartum contribute equally to adverse maternal anthropometric measures 7 y after delivery. Breastfeeding duration may have a beneficial effect.

A critical evaluation of statistical approaches to examining the role of growth trajectories in the developmental origins of health and disease

The developmental origins of health and disease hypothesis suggests that small birth size in conjunction with rapid compensatory childhood growth might yield a greater risk of developing chronic diseases in later life. For example, there is evidence that people who developed coronary heart disease and diabetes experienced different growth trajectories from those who did not develop these diseases. However, some of the methods used in these articles may have been flawed. We critically evaluate proposed approaches for identifying the growth trajectories distinctive to those developing later disease and identifying critical phases of growth during the early lifecourse. Among the approaches we examined (tracing the z-scores, lifecourse plots and models, lifecourse path analysis, conditional body size analysis, multilevel analysis, latent growth curve models and growth mixture models) conditional body size analysis, multilevel analysis, latent growth curve models and growth mixture models are least prone to collinearity problems caused by repeated measures. Multilevel analysis is more flexible when body size is not measured at the same age for all cohort members. Strengths and weaknesses of each approach are illustrated using real data. Demonstrating the influence of growth trajectories on later disease is complex and challenging; therefore, it is likely that a combination of approaches will be required to unravel the complexity in lifecourse research.

A negative feedback model for a mechanism based description of longitudinal observations. Application for bone turnover biomarkers

In modern medicine the diagnosis and prognosis of an abnormal metabolic condition is based on blood borne measurements involving one or more biomarker.

OBJECTIVE

This paper reports the development of a minimal negative feedback model for the description of longitudinal biomarkers concentrations for treatment of osteoporosis in postmenopausal women.

METHODS

Literature data were obtained from double-blind, placebo-controlled clinical trial over three years. There were four treatment groups: 1) Placebo, 2) Alendronate, 3) Conjugated Estrogen, and/or 4) Combination therapy. The negative feedback model consists of a biomarker and a companion controller. By considering the above basal biomarker values it is shown that the dynamics can be described by a second order differential equation without the involvement of biomarker production rate. The second order differential equation is also analogous to classical negative feedback servomechanism model with two parameters ω(n) and ξ. It was assumed that the rate constants defining the negative feedback model were equal which would set ξ to 0.707 with only ω(n) to be estimated.

RESULTS

ω(n) was estimated for both lumbar spine bone mineral density (BMD) and bone-specific alkaline phosphatase (BAP) in four treatments groups. The t(½) of BMD and BAP were estimated at 26.8 (0.30) and 9.4 (0.30) days respectively.

CONCLUSIONS

The negative feedback model of BMD supports the mechanism whereby Conjugated Estrogen and Alendronate decrease the clearance rate constant of BMD analogous to increased apoptosis of osteoclasts. The linked negative feedback models facilitate a mechanism based prediction of BMD using the concentrations of the bone turnover marker BAP.

Modeling obesity histories in cohort analyses of health and mortality

There is great interest in understanding the role of weight dynamics over the life cycle in predicting the incidence of disease and death. Beginning with a Medline search, we identify, classify, and evaluate the major approaches that have been used to study these dynamics. We identify four types of models: additive models, duration-of-obesity models, additive-weight-change models, and interactive models. We develop a framework that integrates the major approaches and shows that they are often nested in one another, a property that facilitates statistical comparisons. Our criteria for evaluating models are two-fold: the model's interpretability and its ability to account for observed variation in health outcomes. We apply two sets of nested models to data on adults age 50-74 years at baseline in two national probability samples drawn from National Health and Nutrition Examination Survey. One set of models treats obesity as a dichotomous variable and the other treats it as a continuous variable. In three of four applications, a fully interactive model does not add significant explanatory power to the simple additive model. In all four applications, little explanatory power is lost by simplifying the additive model to a duration model in which the coefficients of weight at different ages are set equal to one another. Other versions of a duration-of-obesity model also perform well, underscoring the importance of obesity at early adult ages for mortality at older ages.

Maternal serum leptin during pregnancy and infant birth weight: the influence of maternal overweight and obesity

OBJECTIVE

Few studies have examined whether the distinct metabolic patterns found in obese and nonobese pregnant women have different effects on the growing fetus. Our objective was to estimate the influence of longitudinal variation in maternal serum leptin levels on variation in infant birth weight in overweight/obese versus normal-weight women.

DESIGN AND METHODS

In a prospective cohort of 286 gravidas, maternal weight and serum leptin levels at 6-10, 10-14, 16-20, 22-26, and 32-36 weeks gestation were measured. Effects of leptin levels on infant birth weight adjusted for gestational age at delivery (aBW) were analyzed using a linear regression model that accounted for the relationship of time-varying predictors to the log-transformed leptin concentrations.

RESULTS

Different relationships of aBW to maternal serum leptin and its rate of change across pregnancy were exhibited by overweight/obese and normal-weight gravidas. For normal-weight women, aBW is not associated with either the magnitude of the logarithm of the leptin concentration or with its rate of change in either the first or second half of pregnancy. Conversely, for overweight/obese women, an increase in the rate of change in maternal serum leptin in the second half of pregnancy is significantly associated with a decrease in aBW. This effect is distinct from that of maternal weight.

CONCLUSION

Differences in the effect of maternal serum leptin on fetal growth between overweight/ obese and normal-weight women suggest metabolic and physiologic heterogeneity between these groups. Such differences may be involved in the long-term physiologic effects of the obese intrauterine environment on the health of the offspring.

Are gestational age, birth weight, and birth length indicators of favorable fetal growth conditions? A structural equation analysis of Filipino infants

The fetal origins hypothesis emphasizes the life-long health impacts of prenatal conditions. Birth weight, birth length, and gestational age are indicators of the fetal environment. However, these variables often have missing data and are subject to random and systematic errors caused by delays in measurement, differences in measurement instruments, and human error. With data from the Cebu (Philippines) Longitudinal Health and Nutrition Survey, we use structural equation models, to explore random and systematic errors in these birth outcome measures, to analyze how maternal characteristics relate to birth outcomes, and to take account of missing data. We assess whether birth weight, birth length, and gestational age are influenced by a single latent variable that we call favorable fetal growth conditions (FFGC) and if so, which variable is most closely related to FFGC. We find that a model with FFGC as a latent variable fits as well as a less parsimonious model that has birth weight, birth length, and gestational age as distinct individual variables. We also demonstrate that birth weight is more reliably measured than is gestational age. FFGCs were significantly influenced by taller maternal stature, better nutritional stores indexed by maternal arm fat and muscle area during pregnancy, higher birth order, avoidance of smoking, and maternal age 20-35 years. Effects of maternal characteristics on newborn weight, length, and gestational age were largely indirect, operating through FFGC.

The impact of childhood obesity on morbidity and mortality in adulthood: a systematic review

The objective of this study was to evaluate the evidence on whether childhood obesity is a risk factor for adult disease, independent of adult body mass index (BMI). Ovid MEDLINE (1948-May 2011), EMBASE (1980-2011 week 18) and the Cochrane Library (1990-2011) were searched for published studies of BMI from directly measured weight and height in childhood (2-19 years) and disease outcomes in adulthood. Data were synthesized in a narrative fashion. Thirty-nine studies (n 181-1.1 million) were included in the review. There was evidence for associations between childhood BMI and type 2 diabetes, hypertension and coronary heart disease. Few studies examined associations independent of adult BMI; these showed that effect sizes were attenuated after adjustment for adult BMI in standard regression analyses. Although there is a consistent body of evidence for associations between childhood BMI and cardiovascular outcomes, there is a lack of evidence for effects independent of adult BMI. Studies have attempted to examine independent effects using standard adjustment for adult BMI, which is subject to over-adjustment and problems with interpretation. Studies that use more robust designs and analytical techniques are needed to establish whether childhood obesity is an independent risk factor for adult disease.

Maternal weight and body composition during pregnancy are associated with placental and birth weight in rural Bangladesh

Placental growth is a strong predictor of fetal growth, but little is known about maternal predictors of placental growth in malnourished populations. Our objective was to investigate in a prospective study the associations of maternal weight and body composition [total body water (TBW) estimated by bioelectrical impedance and fat and fat-free mass derived from upper arm fat and muscle areas (UAFA, UAMA)] and changes in these with placental and birth weights. Within a cluster-randomized trial of maternal micronutrient supplementation, a subsample of 350 women was measured 3 times across gestation. Longitudinal analysis was used to examine independent associations of ∼10-wk measurements and ∼10-20 wk and ∼20-32 wk changes with birth outcomes. Weight, TBW, and UAMA, but not UAFA, at ∼10 wk were each positively and independently associated with placental weight and birth weight (P < 0.05). Of the maternal ∼10-20 wk changes in measurements, only TBW change and placental weight, and maternal weight and birth weight were positively associated (P < 0.05). Gains in weight, TBW, and UAMA from 20 to 32 wk were positively and UAFA gain was negatively associated with placental weight (P ≤ 0.01). Gains in weight and UAMA from 20 to 32 wk were positively associated with birth weight (P ≤ 0.01). Overall, higher maternal weight and measures of fat-free mass at ∼10 wk gestation and gains from 20 to 32 wk are independently associated with higher placental and birth weight.

Parental height in relation to offspring coronary heart disease: examining transgenerational influences on health using the west of Scotland Midspan Family Study

Background Adult height is known to be inversely related to coronary heart disease (CHD) risk. We sought to investigate transgenerational influence of parental height on offspring’s CHD risk.

Methods Parents took part in a cardiorespiratory disease survey in two Scottish towns during the 1970s, in which their physical stature was measured. In 1996, their offspring were invited to participate in a similar survey, which included an electrocardiogram recording and risk factor assessment.

Results A total of 2306 natural offspring aged 30–59 years from 1456 couples were subsequently flagged for notification of mortality and followed for CHD-related hospitalizations. Taller paternal and/or maternal height was associated with socio-economic advantage, heavier birthweight and increased high-density lipoprotein cholesterol in offspring. Increased height in fathers, but more strongly in mothers (risk ratio for 1 SD change in maternal height = 0.85; 95% confidence interval: 0.76 to 0.95), was associated with a lower risk of offspring CHD, adjusting for age, sex, other parental height and CHD risk factors.

Conclusion There is evidence of an association between taller parental, particularly maternal, height and lower offspring CHD risk. This may reflect an influence of early maternal growth on the intrauterine environment provided for her offspring.

Adolescence risk factors are predictive of coronary artery calcification at middle age: the cardiovascular risk in young Finns study

OBJECTIVES

The purpose of this study was to examine the roles of adolescence risk factors in predicting coronary artery calcium (CAC).

BACKGROUND

Elevated coronary heart disease risk factor levels in adolescence may predict subsequent CAC independently of change in risk factor levels from adolescence to adulthood.

METHODS

CAC was assessed in 589 subjects 40 to 46 years of age from the Cardiovascular Risk in Young Finns Study. Risk factor levels were measured in 1980 (12 to 18 years) and in 2007.

RESULTS

The prevalence of any CAC was 19.2% (27.9% in men and 12.2% in women). Age, levels of systolic blood pressure (BP), total cholesterol, and low-density lipoprotein cholesterol (LDL-C) in adolescence, as well as systolic BP, total cholesterol, diastolic BP, and pack-years of smoking in adulthood were higher among subjects with CAC than those without CAC. Adolescence LDL-C and systolic BP levels predicted CAC in adulthood independently of 27-year changes in these risk factors. The multivariable odds ratios were 1.34 (95% confidence interval: 1.05 to 1.70; p=0.02) and 1.38 (95% confidence interval: 1.08 to 1.77; p=0.01), for 1-SD increase in adolescence LDL-C and systolic BP, respectively. Exposure to both of these risk factors in adolescence (defined as values at or above the age- and sex-specific 75th percentile) substantially increased the risk of CAC (multivariable odds ratio: 3.5 [95% confidence interval: 1.7 to 7.2; p=0.007]) between groups with no versus both risk factors.

CONCLUSIONS

Elevated adolescence LDL-C and systolic BP levels are independent predictors of adulthood CAC, indicating that adolescence risk factor levels play an important role in the pathogenesis of coronary heart disease.

Time issues in multilevel interventions for cancer treatment and prevention

The concept of time introduces important complexities in estimating intervention effects, program and evaluation design, and measurement and analysis of individual change in multilevel interventions (MLIs). Despite growing recognition that time is a critical element for assessing both individual-level outcomes and higher-level changes in organizational, community, and policy contexts, most MLI designs and evaluations have not addressed these issues. In this chapter we discuss 1) conceptualizing disease life-course and treatment theory in MLIs, 2) approaches to incorporating time in research and program design for MLIs in cancer treatment and prevention, 3) analysis of time-varying multilevel data in the context of cancer treatment and prevention, and 4) resource considerations and trade-offs of incorporating time as a dimension of MLIs and analysis. Although analytic techniques for analyzing time-related phenomena are becoming more available and powerful, there has not been corresponding progress made in the development of theory to guide the application of these techniques in program design and implementation.

Socioeconomic position and later life prevalence of hypertension, diabetes and visual impairment in Nakuru, Kenya

OBJECTIVES

We examined the extent to which the association between socioeconomic position (SEP) and later life prevalence of hypertension, diabetes and visual impairment in Nakuru, Kenya is mediated by health-related behaviour.

METHODS

We used data from a community survey of 4,314 participants sampled from urban and rural areas in Nakuru, Kenya. Structural equation modelling was employed to estimate the direct and indirect--via health-related behaviour--effects of SEP on the three health outcomes.

RESULTS

The accumulation of material resources was positively associated with hypertension and diabetes, whereas both education and material resources had a negative association with the prevalence of visual impairment. However, the observed health inequalities were not due to variation between SEP groups in health-related behaviour.

CONCLUSIONS

The pattern of associations between education, material resources and the three health outcomes varied, suggesting that in Kenya, unlike the observed pattern of inequalities in high income countries, different dimensions of SEP provide different aspects of protection as well as risk. Smoking and alcohol use did not appear to mediate the observed associations, in contrast with countries past the epidemiologic transition.

Development of children's internalising and externalising problems from infancy to five years of age

OBJECTIVE

Mental health problems are an international public health issue affecting a substantial proportion of youth. This study aimed to identify groups of young children exhibiting distinct internalising and externalising symptom trajectories across early childhood compared to existing norms. Linear regression then identified child, parenting and family predictors from infancy in the development of internalising and externalising behaviours at age 5 years.

METHOD

This consisted of a follow-up of 5-year-old children from a longitudinal, population-based study with earlier surveys having been completed by primary caregivers when the children were aged 7, 12, 18, 24 and 36 months. Five hundred 5-year-olds (68% retention) were included from 733 children recruited at age 6-7 months from routine well-child appointments across six socio-economically diverse government areas in Victoria, Australia. Mothers then completed a further questionnaire when their children reached 5 years of age, repeating the instruments included in previous waves. The primary outcomes were the Child Behavior Checklist (CBCL), 1.5-5 internalising and externalising symptoms (T-scores in relation to norms) and behaviours (raw scores).

RESULTS

Across early childhood, three distinct profiles for each of the internalising and externalising symptoms (T-scores) were identified and compared to CBCL norms. Around 20% of this Australian child population exhibited consistently elevated symptoms for each problem. Regarding aetiology, longitudinally the strongest predictors of internalising behaviours at 5 years of age were harsh discipline, maternal stress, having no older siblings, single parenthood and maternal substance misuse. The strongest predictors of externalising behaviours at 5 years of age were male sex, harsh discipline and maternal stress. The predictors explained 22% of the variation in internalising behaviours and 24% of the variation in externalising behaviours at 5 years.

CONCLUSIONS

Starting as early as the toddler period, effective population approaches to preventing mental health problems are needed. Randomised trials of preventive interventions focused on improving parenting practices and reducing maternal stress are under way.

The role of longitudinal cohort studies in epigenetic epidemiology: challenges and opportunities

Longitudinal cohort studies are ideal for investigating how epigenetic patterns change over time and relate to changing exposure patterns and the development of disease. We highlight the challenges and opportunities in this approach.

The Norwegian Family Based Life Course (NFLC) study: data structure and potential for public health research

OBJECTIVES

To present details of the Norwegian Family Based Life Course Study.

METHODS

All Norwegians participating in censuses from 1960 to 2001 were included. In addition to the personal identity number, we used household and family information from the 1960 census to link family members together. The NFLC study is further linked to other health registers and surveys.

RESULTS

The proportion included and alive in 1960 increased from 67 % among those born in 1900 to more than 90 % for those born after 1940. In all, 5,266,270 were included. This combined family linkage approach gave 85 % parental linkage for those born in 1940 that dropped to 20 % of those born in 1930. The proportion with misclassified parents was less than 0.5 %. In all, 3,564,582 individuals were linked to their parents.

CONCLUSIONS

The NFLC is one of the largest follow-up of individuals over several decades in their life course. The comprehensive multigenerational, family linkage within the database contributes to large-scale use of various designs for investigating life course determinants.

Birth weight, weight change, and blood pressure during childhood and adolescence: a school-based multiple cohort study

OBJECTIVE

We assessed the association between birth weight, weight change, and current blood pressure (BP) across the entire age-span of childhood and adolescence in large school-based cohorts in the Seychelles, an island state in the African region.

METHODS

Three cohorts were analyzed: 1004 children examined at age 5.5 and 9.1 years, 1886 children at 9.1 and 12.5, and 1575 children at 12.5 and 15.5, respectively. Birth and 1-year anthropometric data were gathered from medical files. The outcome was BP at age 5.5, 9.1, 12.5 or 15.5 years, respectively. Conditional linear regression analysis was used to estimate the relative contribution of changes in weight (expressed in z-score) during different age periods on BP. All analyses were adjusted for height.

RESULTS

At all ages, current BP was strongly associated with current weight. Birth weight was not significantly associated with current BP. Upon adjustment for current weight, the association between birth weight and current BP tended to become negative. Conditional linear regression analyses indicated that changes in weight during successive age periods since birth contributed substantially to current BP at all ages. The strength of the association between weight change and current BP increased throughout successive age periods.

CONCLUSION

Weight changes during any age period since birth have substantial impact on BP during childhood and adolescence, with BP being more responsive to recent than earlier weight changes.

Birth size and childhood growth as determinants of physical functioning in older age: the Helsinki Birth Cohort Study

The study reports on the associations of infant and childhood anthropometric measurements, early growth, and the combined effect of birth weight and childhood body mass index with older age physical functioning among 1,999 individuals born in 1934-1944 and belonging to the Helsinki Birth Cohort Study. Physical functioning was assessed by the Short Form 36 scale. Anthropometric data from infancy and childhood were retrieved from medical records. The risk of lower Short Form 36 physical functioning at the mean age of 61.6 years was increased for those with birth weight less than 2.5 kg compared with those weighing 3.0-3.5 kg at birth (odds ratio (OR) = 2.73, 95% confidence interval (CI): 1.57, 4.72). The gain in weight from birth to age 2 years was associated with decreased risk of lower physical functioning for a 1-standard deviation increase (OR = 0.84, 95% CI: 0.75, 0.94). The risk of lower physical functioning was highest for individuals with birth weight in the lowest third and body mass index at 11 years of age in the highest third compared with those whose birth weight was in the middle third and body mass index at age 11 years was in the highest third (OR = 3.08, 95% CI: 1.83, 5.19). The increasing prevalence of obesity at all ages and the aging of populations warrant closer investigation of the role of weight trajectories in old age functional decline.

Associations of growth trajectories in infancy and early childhood with later childhood outcomes

BACKGROUND

Weight and length at birth (which represent fetal growth) and weight and length or height gain during childhood (which potentially represent catch-up growth) may be related to later health outcomes. However, methods for the assessment of such relations are complex and underdeveloped.

OBJECTIVES

We aimed to describe childhood weight and length or height trajectories and to relate these to later outcomes by using rash at age 6.5 y as an example.

DESIGN

The data came from a prospective cohort study in Belarus in 10,494 children born in 31 hospitals that participated in a cluster randomized trial of breastfeeding promotion. Weight and length or height were measured at birth, at scheduled clinic visits up to 1 y, and at 6.5 y; intermediate measures were obtained from routine child health records. Linear spline multilevel models for weight and length or height were used to estimate each child's deviance from average birth weight, birth length, weight, and length or height gain velocity in each time period. Logistic regression was used to relate the outcome (parental report of rash at 6.5 y) to these weight and length or height estimates.

RESULTS

The best-fitting splines for length or height and weight had knots at 3 and 12 mo, with another knot at 34 mo for height. The only relation between weight and length or height and reported rash was a positive association with weight gain velocity between 12 and 34 mo (odds ratio per SD increase in weight gain velocity: 1.11; 95% CI: 1.01, 1.22).

CONCLUSION

Advantages of multilevel models include no restriction to measures at arbitrary times or to individuals with complete data and allowance for measurement error. This trial was registered at isrctn.org as ISRCTN37687716.

Blood pressure in early adulthood, hypertension in middle age, and future cardiovascular disease mortality: HAHS (Harvard Alumni Health Study)

OBJECTIVES

We sought to examine the association of early adulthood blood pressure with cardiovascular disease (CVD) mortality, while accounting for middle-age hypertension.

BACKGROUND

Elevated blood pressure in middle age is an established CVD risk factor, but evidence for association with measurements earlier in life is sparse.

METHODS

The HAHS (Harvard Alumni Health Study) is a cohort study of 18,881 male university students who had their blood pressure measured at university entry (1914 to 1952; mean age 18.3 years) and who responded to a questionnaire mailed in either 1962 or 1966 (mean age 45.8 years) in which physician-diagnosed hypertension status was reported. Study members were subsequently followed for mortality until the end of 1998.

RESULTS

Following adjustment for age, body mass index, smoking, and physical activity at college entry, compared with men who were normotensive according to the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure criteria (<120/<80 mm Hg), there was an elevated risk of coronary heart disease (CHD) mortality (1,917 deaths) in those who were pre-hypertensive (120 to 139/80 to 89 mm Hg) (hazard ratio [HR]: 1.21; 95% confidence interval [CI]: 1.07 to 1.36), stage 1 (140 to 159/90 to 99 mm Hg) (HR: 1.46; 95% CI: 1.25 to 1.70), and stage 2 hypertensive (≥160/≥100 mm Hg) (HR: 1.89; 95% CI: 1.46 to 2.45), incremental across categories (p(trend) < 0.001). After additionally accounting for middle-age hypertension, estimates were somewhat attenuated, but the pattern remained. Similar associations were apparent for total and CVD mortality, but not stroke mortality.

CONCLUSIONS

Higher blood pressure in early adulthood was associated with elevated risk of all-cause mortality, CVD, and CHD, but not stroke, several decades later. Effects largely persisted after taking into account mediation by middle-age hypertension. Thus, the long-term benefits of blood pressure lowering in early adulthood are promising, but supporting trial data are required.

A life course approach to injury prevention: a "lens and telescope" conceptual model

Background

Although life course epidemiology is increasingly employed to conceptualize the determinants of health, the implications of this approach for strategies to reduce the burden of injuries have received little recognition to date.

Methods

The authors reviewed core injury concepts and the principles of the life course approach. Based on this understanding, a conceptual model was developed, to provide a holistic view of the mechanisms that underlie the accumulation of injury risk and their consequences over the life course.

Results

A "lens and telescope" model is proposed that particularly draws on (a) the extended temporal dimension inherent in the life course approach, with links between exposures and outcomes that span many years, or even generations, and (b) an ecological perspective, according to which the contexts in which individuals live are critical, as are changes in those contexts over time.

Conclusions

By explicitly examining longer-term, intergenerational and ecological perspectives, life course concepts can inform and strengthen traditional approaches to injury prevention and control that have a strong focus on proximal factors. The model proposed also serves as a tool to identify intervention strategies that have co-benefits for other areas of health.

Is infant weight associated with childhood blood pressure? Analysis of the Promotion of Breastfeeding Intervention Trial (PROBIT) cohort

BACKGROUND

Weight gain during infancy may programme later health outcomes, but examination of this hypothesis requires appropriate lifecourse methods and detailed weight gain measures during childhood. We examined associations between weight gain in infancy and early childhood and blood pressure at the age of 6.5 years in healthy children born at term.

METHODS

We carried out an observational analysis of data from a cluster-randomized breastfeeding promotion trial in Belarus. Of 17 046 infants enrolled between June 1996 and December 1997, 13 889 (81.5%) had systolic and diastolic blood pressure measured at 6.5 years; 10 495 children with complete data were analysed. A random-effects linear spline model with three knot points was used to estimate each individual's birthweight and weight gain from birth to 3 months, 3 months to 1 year and 1-5 years. Path analysis was used to separate direct effects from those mediated through subsequent weight gain.

RESULTS

In boys, after controlling for confounders and prior weight gain, the change in systolic blood pressure per z-score increase in weight gain was 0.09 mmHg [95% confidence interval (95% CI) -0.14 to 0.31] for birthweight; 0.41 mmHg (95% CI 0.19-0.64) for birth to 3 months; 0.69 mmHg (95% CI 0.47-0.92) for 3 months to 1 year and 0.82 mmHg (95% CI 0.58-1.06) for 1-5 years. Most of the associations between weight gain and blood pressure were mediated through weight at the age of 6.5 years. Findings for girls and diastolic blood pressure were similar.

CONCLUSIONS

Children who gained weight faster than their peers, particularly at later ages, had higher blood pressure at the age of 6.5 years, with no association between birthweight and blood pressure.

Developmental origins of physical fitness: the Helsinki Birth Cohort Study

Background

Cardiorespiratory fitness (CRF) is a major factor influencing health and disease outcomes including all-cause mortality and cardiovascular disease. Importantly CRF is also modifiable and could therefore have a major public health impact. Early life exposures play a major role in chronic disease development. Our aim was to explore the potential prenatal and childhood origins of CRF in later life.

Methods/Principal Findings

This sub-study of the HBCS (Helsinki Birth Cohort Study) includes 606 men and women who underwent a thorough clinical examination and participated in the UKK 2-km walk test, which has been validated against a maximal exercise stress test as a measure of CRF in population studies. Data on body size at birth and growth during infancy and childhood were obtained from hospital, child welfare and school health records. Body size at birth was not associated with adult CRF. A 1 cm increase in height at 2 and 7 years was associated with 0.21 ml/kg/min (95% CI 0.02 to 0.40) and 0.16 ml/kg/min (95% CI 0.03 to 0.28) higher VO_2max, respectively. Adjustment for adult lean body mass strengthened these findings. Weight at 2 and 7 years and height at 11 years became positively associated with CRF after adult lean body mass adjustment. However, a 1 kg/m² higher BMI at 11 years was associated with −0.57 ml/kg/min (95% CI −0.91 to −0.24) lower adult VO_2max, and remained so after adjustment for adult lean body mass.

Conclusion/Significance

We did not observe any significant associations between body size at birth and CRF in later life. However, childhood growth was associated with CRF in adulthood. These findings suggest, importantly from a public point of view, that early growth may play a role in predicting adult CRF.

Objectively measured physical activity and the subsequent risk of incident dysglycemia: the Australian Diabetes, Obesity and Lifestyle Study (AusDiab)

OBJECTIVE

To investigate pedometer-measured physical activity (PA) in 2000 and change in PA over 5 years with subsequent risk of dysglycemia by 2005.

RESEARCH DESIGN AND METHODS

This prospective cohort study in Tasmania, Australia, analyzed 458 adults with normal glucose tolerance and a mean (SD) age of 49.7 (12.1) years in 2000. Variables assessed in 2000 and 2005 included PA, by pedometer and questionnaire, nutrient intake, and other lifestyle factors. Incident dysglycemia was defined as the development of impaired fasting glucose or impaired glucose tolerance revealed by oral glucose tolerance testing in 2005, without type 2 diabetes.

RESULTS

Incident dysglycemia developed in 26 participants during the 5-year period. Higher daily steps in 2000 were independently associated with a lower 5-year risk of incident dysglycemia (adjusted odds ratio [AOR] 0.87 [95% CI 0.77-0.97] per 1,000-step increment). Higher daily steps in 2005, after controlling for baseline steps in 2000 (thus reflecting change in steps over 5 years), were not associated with incident dysglycemia (AOR 1.02 [0.92-1.14]). Higher daily steps in 2000 were also associated with lower fasting blood glucose, but not 2-h plasma glucose by 2005. Further adjustment for BMI or waist circumference did not remove these associations.

CONCLUSIONS

Among community-dwelling adults, a higher rate of daily steps is associated with a reduced risk of incident dysglycemia. This effect appears to be not fully mediated through reduced adiposity.