Population-level trends in the distribution of body mass index in England, 1992-2013.

BACKGROUND: Changes over time of mean body weight or prevalence of overweight and obesity have been well documented. Less consideration has been given to describing the distribution to these changes particularly by socioeconomic status and sex. METHODS: We use data from the Health Survey for England for the years 1992-2013 to calculate the median, 5th and 95th centiles, and SD of body mass index (BMI). We tested differences using analysis of variance and quantile regression. Analyses were stratified by sex and level of education. RESULTS: There have been increases in the SD of BMI values over the period. While median BMI has increased, there has been a larger increase of the 95th centile. These trends were consistent by sex and level of education, although significant differences were observed in values. CONCLUSIONS: Our results demonstrate that changes in median BMI over time do not reflect changes in the distribution of BMI. Failing to understand the distribution of body weight in the population will hamper our projections of future patterns, as well as our ability to design effective public health strategies.