Lina W. Olsen

Age at puberty and the emerging obesity epidemic.

Background Recent studies have shown that puberty starts at younger ages than previously. It has been hypothesized that the increasing prevalence of childhood obesity is contributing to this trend. The purpose of this study was to analyze the association between prepubertal body mass index (BMI) and pubertal timing, as assessed by age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV), and the secular trend of pubertal timing given the prepubertal BMI. Methodology/Principal Findings Annual measurements of height and weight were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen municipality; 156,835 children fulfilled the criteria for determining age at OGS and PHV. The effect of prepubertal BMI at age seven on these markers of pubertal development within and between birth cohorts was analyzed. BMI at seven years was significantly inversely associated with age at OGS and PHV. Dividing the children into five levels of prepubertal BMI, we found a similar secular trend toward earlier maturation in all BMI groups. Conclusion/Significance The heavier both boys and girls were at age seven, the earlier they entered puberty. Irrespective of level of BMI at age seven, there was a downward trend in the age at attaining puberty in both boys and girls, which suggests that the obesity epidemic is not solely responsible for the trend.

Birth weight and risk of cancer

It is well established that prenatal biologic processes are important for the development of some childhood cancers, whereas less is known regarding their influence on adult cancer risk. High birth weight has been associated with risk of breast cancer, whereas studies of other specific cancers and all cancers together have been less conclusive.

Weight at birth and all-cause mortality in adulthood.

Background: Small size at birth is associated with subsequent cardiovascular disease and diabetes, and large size is associated with obesity and cancer. The overall impact of these opposing effects on mortality throughout the lifespan is unclear because causes of death change with age. Methods: We investigated the association of birth weight with adult all-cause mortality using a Danish school-based cohort of 216,464 men and women born from 1936 through 1979. The cohort was linked to vital statistic registers. The main outcome was all-cause mortality from ages 25 through 68 years. Associations with death from cancer, circulatory disease, and all other causes were also examined. Results: During 5,205,477 person-years of follow-up, 11,149 deaths occurred among men and 6609 among women. The cumulative hazard ratios of the association between birth weight categories and all-cause mortality was constant for all ages investigated and did not differ between men and women. Compared with subjects having birth weights in the reference category (3251–3750 g), those with the lowest birth weights (2000–2750 g) had 17% higher mortality (95% confidence interval = 1.11–1.22), and those with the highest birth weights (4251–5500 g) had 7% higher mortality (1.01–1.15) from all causes. The association of birth weight with cancer increased linearly, whereas the association of birth weight with circulatory disease and all other causes was U-shaped. Conclusions: To the degree that the association of birth weight with adult survival is causal, the U-shaped association between birth weight and adult mortality suggests that population increases in birth weight may not necessarily lead to improved health in adulthood.

Forty Years Trends in Timing of Pubertal Growth Spurt in 157,000 Danish School Children

Background Entering puberty is an important milestone in reproductive life and secular changes in the timing of puberty may be an important indicator of the general reproductive health in a population. Too early puberty is associated with several psychosocial and health problems. The aim of our study was to determine if the age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV) during puberty show secular trends during four decades in a large cohort of school children. Methods and Findings Annual measurements of height were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen Municipality. 135,223 girls and 21,612 boys fulfilled the criteria for determining age at OGS and age at PHV. These physiological events were used as markers of pubertal development in our computerized method in order to evaluate any secular trends in pubertal maturation during the study period (year of birth 1930 to 1969). In this period, age at OGS declined statistically significantly by 0.2 and 0.4 years in girls and boys, respectively, whereas age at PHV declined statistically significantly by 0.5 and 0.3 years in girls and boys, respectively. The decline was non-linear with a levelling off in the children born between 1940 and 1955. The duration of puberty, as defined by the difference between age at OGS and age at PHV, increased slightly in boys, whereas it decreased in girls. Conclusion Our finding of declining age at OGS and at PHV indicates a secular trend towards earlier sexual maturation of Danish children born between 1930 and 1969. Only minor changes were observed in duration of puberty assessed by the difference in ages at OGS and PHV.

Cohort Profile: The Copenhagen School Health Records Register

The Copenhagen School Health Records Register(CSHRR) is a database of health examination infor-mation on more than 350000 schoolchildren who everattended school in the central municipality of thecapital city of Denmark. For longer than 100 years,school-based health care has been provided to chil-dren in Copenhagen,

Secular Trends in Childhood Obesity in Denmark During 50 Years in Relation to Economic Growth

Objective: Our aim was to examine whether secular trends in childhood overweight and obesity during five decades could be explained by economic growth.

Birth cohort effect on the obesity epidemic in Denmark

Background: In Denmark, the obesity epidemic has developed in phases. To investigate if this has been a birth cohort phenomenon, we explored the secular trend in the prevalence of obesity among boys and young men. Methods: We calculated body mass index (BMI; kg/m2) over time for 163,835 Danish boys examined at ages 7–11 years and for 708,342 male draftees examined at age 19 years. Obesity was defined according to age-specific criteria for boys and as BMI ≥31 kg/m2 for men. We examined trends in the prevalence of obesity from 1930 through 1999, expressing time as the subjects’ year of measurement and as year of birth. Results: When expressed by year of measurement, 4 phases in the prevalence of obesity emerged for the boys and the young men, but they occurred at different times. However, when expressed by year of birth, the 2 stable periods and the 2 periods with sharp increases in obesity occurred in the same birth years. An increased prevalence of obesity was identified for birth cohorts from the early 1940s to the mid-1950s and from the late 1960s onward. Conclusions: The trends in the prevalence of obesity were similar in boys and young men only when expressed by year of birth, which suggests that early life may be a susceptible period for developing obesity. Specifically, the increased prevalence of obesity observed for birth cohorts from the early 1940s to the mid-1950s and from the late 1960s onward suggests that changes in the early life of these cohorts resulted in an increase in obesity at later ages.