Contributions of incidence and persistence to the prevalence of childhood obesity during the emerging epidemic in Denmark.

BACKGROUND: Prevalence of obesity is the result of preceding incidence of newly developed obesity and persistence of obesity. We investigated whether increasing incidence and/or persistence during childhood drove the prevalence of childhood obesity during the emerging epidemic. METHODS: Height and weight were measured at ages 7 and 13 years in 192,992 Danish school children born 1930-1969. Trends in the incidence (proportion obese at 13 years among those not obese at 7 years) and persistence (proportion obese at 13 years among those obese at 7 years) across birth cohort periods (1930-41 with low stable prevalence of obesity, 1942-51 with increasing prevalence, 1952-69 with the higher, but stable prevalence) were investigated. Logistic regression was used to examine the associations between BMI at 7 years as a continuous trait, allowing interactions with the birth cohorts, and occurrence of obesity at 13 years. RESULTS: The prevalence of obesity was similar at 7 and 13 years and increased across birth cohorts in boys from around 0.1% to 0.5% and in girls from around 0.3% to 0.7%. The incidence of obesity between ages 7 and 13 years increased from 0.15% to 0.35% in boys and from 0.20% to 0.44% in girls. The persistence increased from 28.6% to 41.4% in boys and from 16.4% to 31.0% in girls. Despite a decrease over time, the remission of obesity occurred in >60% of obese children in the last birth cohort. However, the odds ratios of obesity at age 13 years in relation to the full range of BMI at 7 years remained unchanged across the birth cohort periods. CONCLUSIONS/SIGNIFICANCE: The development of the obesity epidemic in children was due to an increase in both incidence and persistence of obesity. Contrary to prevailing expectations, a large, although declining, proportion of children obese at an early age underwent remission during childhood.

Birth weight, childhood body mass index and risk of coronary heart disease in adults: combined historical cohort studies.

BACKGROUND: Low birth weight and high childhood body mass index (BMI) is each associated with an increased risk of coronary heart disease (CHD) in adult life. We studied individual and combined associations of birth weight and childhood BMI with the risk of CHD in adulthood. METHODS/PRINCIPAL FINDINGS: Birth weight and BMI at age seven years were available in 216,771 Danish and Finnish individuals born 1924-1976. Linkage to national registers for hospitalization and causes of death identified 8,805 CHD events during up to 33 years of follow-up (median = 24 years) after age 25 years. Analyses were conducted with Cox regression based on restricted cubic splines. Using median birth weight of 3.4 kg as reference, a non-linear relation between birth weight and CHD was found. It was not significantly different between cohorts, or between men and women, nor was the association altered by childhood BMI. For birth weights below 3.4 kg, the risk of CHD increased linearly and reached 1.28 (95% confidence limits: 1.13 to 1.44) at 2 kg. Above 3.4 kg the association weakened, and from about 4 kg there was virtually no association. BMI at age seven years was strongly positively associated with the risk of CHD and the relation was not altered by birth weight. The excess risk in individuals with a birth weight of 2.5 kg and a BMI of 17.7 kg/m(2) at age seven years was 44% (95% CI: 30% to 59%) compared with individuals with median values of birth weight (3.4 kg) and BMI (15.3 kg/m(2)). CONCLUSIONS/SIGNIFICANCE: Birth weight and BMI at age seven years appeared independently associated with the risk of CHD in adulthood. From a public health perspective we suggest that particular attention should be paid to children with a birth weight below the average in combination with excess relative weight in childhood.

Birth weight in relation to leisure time physical activity in adolescence and adulthood: meta-analysis of results from 13 nordic cohorts.

BACKGROUND: Prenatal life exposures, potentially manifested as altered birth size, may influence the later risk of major chronic diseases through direct biologic effects on disease processes, but also by modifying adult behaviors such as physical activity that may influence later disease risk. METHODS/PRINCIPAL FINDINGS: We investigated the association between birth weight and leisure time physical activity (LTPA) in 43,482 adolescents and adults from 13 Nordic cohorts. Random effects meta-analyses were performed on categorical estimates from cohort-, age-, sex- and birth weight specific analyses. Birth weight showed a reverse U-shaped association with later LTPA; within the range of normal weight the association was negligible but weights below and above this range were associated with a lower probability of undertaking LTPA. Compared with the reference category (3.26-3.75 kg), the birth weight categories of 1.26-1.75, 1.76-2.25, 2.26-2.75, and 4.76-5.25 kg, had odds ratios of 0.67 (95% confidence interval: 0.47, 0.94), 0.72 (0.59, 0.88), 0.89 (0.79, 0.99), and 0.65 (0.50, 0.86), respectively. The shape and strength of the birth weight-LTPA association was virtually independent of sex, age, gestational age, educational level, concurrent body mass index, and smoking. CONCLUSIONS/SIGNIFICANCE: The association between birth weight and undertaking LTPA is very weak within the normal birth weight range, but both low and high birth weights are associated with a lower probability of undertaking LTPA, which hence may be a mediator between prenatal influences and later disease risk.

Child care is not a substantial risk factor for gastrointestinal infection hospitalization.

OBJECTIVE: The objective was to study the effect of age at first enrollment into child care and other child care-related factors on the risk for hospitalization from gastrointestinal infection. METHODS: This was a population-based prospective cohort study of 1,110,973 Danish children aged 0 to 5 years in the period 1989-2004. By means of Poisson regression, risk for gastrointestinal infection hospitalization was evaluated by incidence rate ratio and 95% confidence intervals. RESULTS: Overall, children who were attending child care had an IRR of gastrointestinal infection hospitalization of 1.02 compared with children in home care. When compared within the group of children who attended child care, those who were enrolled after 18 months of age had a slightly increased risk compared with those who were enrolled before 1 year of age. The first 5 months of enrollment were associated with an IRR of 1.18 compared with later periods, and similar risks were observed in different types of child care facilities. The effect of child care was similar in most strata of the studied child, family, and demographic variables; however, children younger than 1 year who attended child care had an IRR of 1.44 compared with children of the same age in home care. Well established risk factors for gastrointestinal infection such as young age and male gender were reproduced; compared with 5-year-olds, children younger than 1 year had an IRR of 7.37 and boys had an IRR of 1.18 compared with girls. CONCLUSIONS: The results of this study suggest that child care attendance is not a substantial risk factor for gastrointestinal infection hospitalization in most Danish children. Late enrollment and the first short period of enrollment were associated with a slightly increased risk for gastrointestinal infection hospitalization.