A new study in Norway has revealed that while teenagers have grown taller and put on weight in the last three decades, the problem of underweight teens has also increased significantly.
Sigrid Bjørnelv of the Norwegian University of Science and Technology and colleagues conducted a study to analyse the height, weight, and body-mass index (BMI) of adolescents during 1966-1969 and 1995-1997 in Norway. The study demonstrated a shift towards taller and heavier teenagers, but also hints that there are more underweight adolescents.
In weight related health studies, health researchers commonly use body mass index (BMI), calculated as weight in kilograms divided by the height in meters squared.
The researchers have said that changes in these measurements across society over periods of time often reflect changes in nutrition. Better nutrition increases both height and weight, and reduces health problems associated with malnutrition. However, increases in BMI can also point to poor diet and lack of exercise.
They research team therefore conducted a study where they analysed height, weight and calculated BMI data for 6774 14-18-year olds who participated in the Young-HUNT study in 1995-97. They compared the data with 8378 adolescents in the same age group collected by Norway's National Health Screening Service in 1966-69.
As a result of the analysis, the research team found significant changes between the two periods. Height and weight increased significantly in both sexes and all ages, while average (mean) BMI increased significantly in boys of all ages but only in 18-year old girls. Mean BMI did not change for girls aged 14-17 years. Critically, the team revealed a change in distribution of BMI, with an increase in the upper percentile values and a decrease in the lower percentile values.
Bjørnelv said, while the increase in the highest percentile implies better nutrition and an increase in prevalence of obesity amongst adolescents in agreement with other studies, the decrease in the lower percentile values implies that the thinnest adolescents in 1995-97 had a lower BMI than their counterparts in 1967-69. This finding requires further study.
The study appears in the online open access journal BMC Public Health suggests.