Regression models for linking patterns of growth to a later outcome: infant growth and childhood overweight.

BACKGROUND: Regression models are widely used to link serial measures of anthropometric size or changes in size to a later outcome. Different parameterisations of these models enable one to target different questions about the effect of growth, however, their interpretation can be challenging. Our objective was to formulate and classify several sets of parameterisations by their underlying growth pattern contrast, and to discuss their utility using an expository example. METHODS: We describe and classify five sets of model parameterisations in accordance with their underlying growth pattern contrast (conditional growth; being bigger v being smaller; becoming bigger and staying bigger; growing faster v being bigger; becoming and staying bigger versus being bigger). The contrasts are estimated by including different sets of repeated measures of size and changes in size in a regression model. We illustrate these models in the setting of linking infant growth (measured on 6 occasions: birth, 6 weeks, 3, 6, 12 and 24 months) in weight-for-height-for-age z-scores to later childhood overweight at 8y using complete cases from the Norwegian Childhood Growth study (n = 900). RESULTS: In our expository example, conditional growth during all periods, becoming bigger in any interval and staying bigger through infancy, and being bigger from birth were all associated with higher odds of later overweight. The highest odds of later overweight occurred for individuals who experienced high conditional growth or became bigger in the 3 to 6 month period and stayed bigger, and those who were bigger from birth to 24 months. Comparisons between periods and between growth patterns require large sample sizes and need to consider how to scale associations to make comparisons fair; with respect to the latter, we show one approach. CONCLUSION: Studies interested in detrimental growth patterns may gain extra insight from reporting several sets of growth pattern contrasts, and hence an approach that incorporates several sets of model parameterisations. Co-efficients from these models require careful interpretation, taking account of the other variables that are conditioned on.

Important periods of weight development in childhood: a population-based longitudinal study.

BACKGROUND: Identifying important ages for the development of overweight is essential for optimizing preventive efforts. The purpose of the study was to explore early growth characteristics in children who become overweight or obese at the age of 8 years to identify important ages for the onset of overweight and obesity. METHODS: Data from the Norwegian Child Growth Study in 2010 (N = 3172) were linked with repeated measurements from health records beginning at birth. Weight and height were used to derive the body mass index (BMI) in kg/m2. The BMI standard deviation score (SDS) for each participant was estimated at specific target ages, using a piecewise linear mixed effect model. RESULTS: At 8 years of age, 20.4% of the children were overweight or obese. Already at birth, overweight children had a significantly higher mean BMI SDS than normal weight 8-year-olds (p < .001) and this difference increased in consecutive age groups in infancy and childhood. A relatively large increase in BMI during the first 9 months was identified as important for being overweight at 8 years. BMI SDS at birth was associated with overweight at 8 years of age (OR, 1.8; 1.6-2.0), and with obesity (OR, 1.8; 1.4-2.3). The Odds Ratios for the BMI SDS and change in BMI SDS further increased up to 1 year of age became very high from 2 years of age onwards. CONCLUSIONS: A high birth weight and an increasing BMI SDS during the first 9 months and high BMI from 2 years of age proved important landmarks for the onset of being overweight at 8 years of age. The risks of being overweight at 8 years appear to start very early. Interventions to prevent children becoming overweight should not only start at a very early age but also include the prenatal stage.

WHO European Childhood Obesity Surveillance Initiative: body mass index and level of overweight among 6-9-year-old children from school year 2007/2008 to school year 2009/2010.

BACKGROUND: The World Health Organization (WHO) Regional Office for Europe has established the Childhood Obesity Surveillance Initiative (COSI) to monitor changes in overweight in primary-school children. The aims of this paper are to present the anthropometric results of COSI Round 2 (2009/2010) and to explore changes in body mass index (BMI) and overweight among children within and across nine countries from school years 2007/2008 to 2009/2010. METHODS: Using cross-sectional nationally representative samples of 6-9-year-olds, BMI, anthropometric Z-scores and overweight prevalence were derived from measured weight and height. Significant changes between rounds were assessed using variance and t-tests analyses. RESULTS: At Round 2, the prevalence of overweight (including obesity; WHO definitions) ranged from 18% to 57% among boys and from 18% to 50% among girls; 6 - 31% of boys and 5 - 21% of girls were obese. Southern European countries had the highest overweight prevalence. Between rounds, the absolute change in mean BMI (range: from -0.4 to +0.3) and BMI-for-age Z-scores (range: from -0.21 to +0.14) varied statistically significantly across countries. The highest significant decrease in BMI-for-age Z-scores was found in countries with higher absolute BMI values and the highest significant increase in countries with lower BMI values. The highest significant decrease in overweight prevalence was observed in Italy, Portugal and Slovenia and the highest significant increase in Latvia and Norway. CONCLUSIONS: Changes in BMI and prevalence of overweight over a two-year period varied significantly among European countries. It may be that countries with higher prevalence of overweight in COSI Round 1 have implemented interventions to try to remedy this situation.

Adiposity among children in Norway by urbanity and maternal education: a nationally representative study.

BACKGROUND: International research has demonstrated that rural residency is a risk factor for childhood adiposity. The main aim of this study was to investigate the urban-rural gradient in overweight and obesity and whether the association differed by maternal education. METHODS: Height, weight and waist circumference (WC) were measured in a nationally representative sample of 3166 Norwegian eight-year-olds in 2010. Anthropometric measures were stratified by area of residence (urbanity) and maternal education. Risk estimates for overweight (including obesity) and waist-to-height ratio ≥0.5 were calculated by log-binomial regression. RESULTS: Mean BMI and WC and risk estimates of overweight (including obesity) and waist-to-height ratio ≥0.5 were associated with both urbanity and maternal education. These associations were robust after mutual adjustment for each other. Furthermore, there was an indication of interaction between urbanity and maternal education, as trends of mean BMI and WC increased from urban to rural residence among children of low-educated mothers (p = 0.01 for both BMI and WC), whereas corresponding trends for children from higher educational background were non-significant (p > 0.30). However, formal tests of the interaction term urbanity by maternal education were non-significant (p-value for interaction was 0.29 for BMI and 0.31 for WC). CONCLUSIONS: In this nationally representative study, children living rurally and children of low-educated mothers had higher mean BMI and waist circumference than children living in more urban areas and children of higher educated mothers.

Impact of instrument error on the estimated prevalence of overweight and obesity in population-based surveys.

BACKGROUND: The basis for this study is the fact that instrument error increases the variance of the distribution of body mass index (BMI). Combined with a defined cut-off value this may impact upon the estimated proportion of overweight and obesity. It is important to ensure high quality surveillance data in order to follow trends of estimated prevalence of overweight and obesity. The purpose of the study was to assess the impact of instrument error, due to uncalibrated scales and stadiometers, on prevalence estimates of overweight and obesity. METHODS: Anthropometric measurements from a nationally representative sample were used; the Norwegian Child Growth study (NCG) of 3474 children. Each of the 127 participating schools received a reference weight and a reference length to determine the correction value. Correction value corresponds to instrument error and is the difference between the true value and the measured, uncorrected weight and height at local scales and stadiometers. Simulations were used to determine the expected implications of instrument errors. To systematically investigate this, the coefficient of variation (CV) of instrument error was used in the simulations and was increased successively. RESULTS: Simulations showed that the estimated prevalence of overweight and obesity increased systematically with the size of instrument error when the mean instrument error was zero. The estimated prevalence was 16.4% with no instrument error and was, on average, overestimated by 0.5 percentage points based on observed variance of instrument error from the NCG-study. Further, the estimated prevalence was 16.7% with 1% CV of instrument error, and increased to 17.8%, 19.5% and 21.6% with 2%, 3% and 4% CV of instrument error, respectively. CONCLUSIONS: Failure to calibrate measuring instruments is likely to lead to overestimation of the prevalence of overweight and obesity in population-based surveys.

[Overweight children--how important is the urban/rural factor?]. / Overvekt hos barn--hvilken betydning har bosted?

BACKGROUND: Targeted measures to prevent overweight children are dependent on a knowledge of which environmental factors play a part. We wanted to investigate whether overweight in Norwegian eight-year-olds is related to whether they live in urban or rural areas. MATERIAL AND METHOD: In the cross-sectional study "Children's growth in Norway 2008", the weight, height and waist of 3473 eight-year-olds were measured. We examined relationships between overweight and waist measurement and centrality, population density and number of inhabitants in the municipalities where the children lived by means of regression analyses. RESULT: In adjusted analyses, the odds on children in central municipalities being overweight was 34 lower than for children in less central municipalities (OR = 0.66; 95 % CI: 0.46-0.94), and children in municipalities with a high population density had on average 0.66 cm smaller waists than children in municipalities with a low population density (95 % CI: 0.02-1.31). The relationships between overweight and the explanatory variables population density and number of inhabitants, and between waist measurement and the explanatory variables centrality and population density showed the same tendency, but were not statistically significant in the adjusted analyses. INTERPRETATION: The results indicate that there is a higher percentage of overweight children in rural areas than in urban areas. Education and income level in the municipalities appeared to explain some of the effect of the urbanity variables on overweight and waist measurement.

Childhood abuse and later worries about the baby's health in pregnancy.

OBJECTIVE: to explore the associations between sexual and/or physical abuse in childhood and worries about the baby's health in pregnancy. DESIGN: cross-sectional questionnaire study. Setting. Norwegian prospective pregnancy cohort. SAMPLE: an original sample of 58,139 pregnancies (1999-2006) covering about 43% of the pregnant population. METHODS: two self-reported questionnaires in the 17th and 30th week of gestation were merged with data from the Medical Birth Registry of Norway. Associations between physical and/or sexual childhood abuse and worries about the baby's health were assessed with multiple logistic regression analyses. MAIN OUTCOME MEASURES: strong worries about the baby's health in the 30th week of gestation among women with experience of childhood abuse. RESULTS: women who reported being exposed to physical or sexual childhood abuse or a combination of the two were at increased risk of strong worries about the baby's health compared to women who had not been similarly exposed (adjusted odds ratio (OR) = 1.62, 95% confidence interval (CI) 1.26-2.08; adjusted OR = 1.30, 95% CI 1.03-1.64; adjusted OR = 2.10, 95% CI 1.68-2.62, respectively). Marital status, adult abuse, pelvic pain, quality of antenatal care, self-efficacy and previous birth experiences were also associated with concern about the baby's health. CONCLUSIONS: there were significant associations between physical and/or sexual childhood abuse and strong concern about the baby's health. Worries about the baby's health are complex and associated with many elements of risk.

Social differences in smoking and snuff use among Norwegian adolescents: a population based survey.

BACKGROUND: A change in pattern of tobacco use has been observed in the last decade in Norway. Snuff use and occasional smoking have to some degree replaced daily smoking among adolescents and young adults. Daily smoking is known to be negatively associated with social background factors, but little is known about these associations for other types of tobacco use. Our aim was to study different types of tobacco use among adolescents according to gender, educational ambitions, family background factors, and urbanization. METHODS: Cross-sectional, school-based study with 15 931 participants and response-rate 87%, conducted among 15 and 16 year olds during 2000-2004. RESULTS: More girls (33.8%) than boys (26.4%) were daily or occasional smokers, while more boys (21.4%) than girls (3.5%) were daily or occasional snuff users. Daily smoking was more common among adolescents planning vocational education, with single parents or poor family economy. Occasional smoking and snuff use (daily or occasionally) showed a similar, but less pronounced pattern regarding education and single parent families. Adolescents with parents from foreign countries were less likely to use tobacco. One exception was boys with parents from Muslim majority countries who had an increased risk of daily smoking. A typical combination user of both tobacco types was a Norwegian boy with divorced parents and ambitions to complete vocational studies or only one year of upper secondary school. CONCLUSION: Tobacco use in adolescents is mainly associated with low educational ambitions and less affluent self-reported family economy. Adolescents with divorced parents use more tobacco than those living with both parents. Public health initiatives to avoid or reduce tobacco use should mainly target adolescents in vocational studies and those leaving school early.

[Occasional smoking--an increasing problem]. / Av-og-til-røyking--et økende problem.

Little attention is given to occasional smoking compared with daily smoking. However, there are indications that there is a continuous increase in occasional smoking throughout the western world. In Norway, 33% of smokers do not smoke daily. Little is known about these smokers' background, how often they smoke, and how many cigarettes they consume when they do smoke. Studies indicate that occasional smokers seem to differ from regular smokers in their socio-demographic characteristics. In this article we show that a proportion of the occasional smokers smoke more than previously assumed. Therefore this smoking pattern may have greater implications for health than previously assumed and can no longer be ignored.

Parental marital status and childhood overweight and obesity in Norway: a nationally representative cross-sectional study.

OBJECTIVE: Sociodemographic changes in Norway and other western industrialised countries, including family structure and an increasing proportion of cohabiting and divorced parents, might affect the prevalence of childhood overweight and obesity issues. We aimed to examine whether parental marital status was associated with general and abdominal obesity among children. We also sought to explore whether the associations differed by gender. DESIGN: Cross-sectional. SETTING: 127 primary schools across Norway. PARTICIPANT: 3166 third graders (mean age 8.3 years) participating in the nationally representative Norwegian Child Growth Study in 2010. MEASUREMENTS: Height, weight and waist circumference were objectively measured. The main outcome measures were general overweight (including obesity; body mass index ≥25 kg/m(2)) using International Obesity Task Force (IOTF) cut-offs and abdominal obesity (waist-to-height ratio ≥0.5) by gender and parental marital status. Prevalence ratios, adjusted for possible confounders, were calculated by log-binomial regression. RESULTS: General overweight (including obesity) was 1.54 (95% CI 1.21 to 1.95) times more prevalent among children of divorced parents compared with children of married parents, and the corresponding prevalence ratio for abdominal obesity was 1.89 (95% CI 1.35 to 2.65). Formal tests of the interaction term parental marital status by gender were not statistically significant. However, in gender-specific analyses the association between parental marital status and adiposity measures was only statistically significant in boys (p=0.04 for general overweight (including obesity) and p=0.01 for abdominal obesity). The estimates were robust against adjustment for maternal education, family country background and current area of residence. CONCLUSIONS: General and abdominal obesities were more prevalent among children of divorced parents. This study provides valuable information by focusing on societal changes in order to identify vulnerable groups.

WHO European Childhood Obesity Surveillance Initiative: School nutrition environment and body mass index in primary schools.

BACKGROUND: Schools are important settings for the promotion of a healthy diet and sufficient physical activity and thus overweight prevention. OBJECTIVE: To assess differences in school nutrition environment and body mass index (BMI) in primary schools between and within 12 European countries. METHODS: Data from the World Health Organization (WHO) European Childhood Obesity Surveillance Initiative (COSI) were used (1831 and 2045 schools in 2007/2008 and 2009/2010, respectively). School personnel provided information on 18 school environmental characteristics on nutrition and physical activity. A school nutrition environment score was calculated using five nutrition-related characteristics whereby higher scores correspond to higher support for a healthy school nutrition environment. Trained field workers measured children's weight and height; BMI-for-age (BMI/A) Z-scores were computed using the 2007 WHO growth reference and, for each school, the mean of the children's BMI/A Z-scores was calculated. RESULTS: Large between-country differences were found in the availability of food items on the premises (e.g., fresh fruit could be obtained in 12%-95% of schools) and school nutrition environment scores (range: 0.30-0.93). Low-score countries (Bulgaria, Czech Republic, Greece, Hungary, Latvia and Lithuania) graded less than three characteristics as supportive. High-score (≥0.70) countries were Ireland, Malta, Norway, Portugal, Slovenia and Sweden. The combined absence of cold drinks containing sugar, sweet snacks and salted snacks were more observed in high-score countries than in low-score countries. Largest within-country school nutrition environment scores were found in Bulgaria, Czech Republic, Greece, Hungary, Latvia and Lithuania. All country-level BMI/A Z-scores were positive (range: 0.20-1.02), indicating higher BMI values than the 2007 WHO growth reference. With the exception of Norway and Sweden, a country-specific association between the school nutrition environment score and the school BMI/A Z-score was not observed. CONCLUSIONS: Some European countries have implemented more school policies that are supportive to a healthy nutrition environment than others. However, most countries with low school nutrition environment scores also host schools with supportive school environment policies, suggesting that a uniform school policy to tackle the "unhealthy" school nutrition environment has not been implemented at the same level throughout a country and may underline the need for harmonized school policies.

The biobank of the Norwegian Mother and Child Cohort Study: a resource for the next 100 years.

INTRODUCTION: Long-term storage of biological materials is a critical component of any epidemiological study. In designing specimen repositories, efforts need to balance future needs for samples with logistical constraints necessary to process and store samples in a timely fashion. OBJECTIVES: In the Norwegian Mother and Child Cohort Study (MoBa), the Biobank was charged with long-term storage of more than 380,000 biological samples from pregnant women, their partners and their children for up to 100 years. METHODS: Biological specimens include whole blood, plasma, DNA and urine; samples are collected at 50 hospitals in Norway. All samples are sent via ordinary mail to the Biobank in Oslo where the samples are registered, aliquoted and DNA extracted. DNA is stored at -20 degrees C while whole blood, urine and plasma are stored at -80 degrees C. RESULTS: As of July 2006, over 227,000 sample sets have been collected, processed and stored at the Biobank. Currently 250-300 sets are received daily. An important part of the Biobank is the quality control program. CONCLUSION: With the unique combination of biological specimens and questionnaire data, the MoBa Study will constitute a resource for many future investigations of the separate and combined effects of genetic, environmental factors on pregnancy outcome and on human morbidity, mortality and health in general.