There are a number of reference data sets for BMI in childhood. In many countries, BMI reference data are used or recommended as part of monitoring children’s growth (2
). Such reference data are often based on representative data from a given country. For example, data for weight, height, BMI, and head circumference from 37,000 children from surveys representative of England, Scotland, and Wales were used to develop the 1990 British growth reference (22
In the United States, the CDC 2000 growth charts for the US were developed from 5 nationally representative survey data sets (the National Health Examination Surveys II and III in the 1960s, the NHANES I and II in the 1970s, and NHANES III, 1988–1994) (23
). WHO subsequently used much of the same NHANES data to develop growth standards for older children and adolescents (24
). The 2000 CDC charts are revised versions of the 1977 National Center for Health Statistics growth charts (23
In 2006 WHO released a new set of growth charts for children from birth through 5 y of age based on data from the Multicentre Growth Reference Study conducted by WHO (25
). The WHO charts are based on different principles than the aforementioned national growth charts. The WHO charts are intended to serve as growth standards, describing how children should grow. In contrast, many national charts are descriptive, describing how children in the reference population did grow. The WHO charts are based on a highly selective sample of children from 6 sites around the world, consisting of children who were not subjected to socioeconomic constraints on growth, who were healthy term singleton births, whose mothers did not smoke before, during, or after pregnancy, and who were fed according to Multicentre Growth Reference Study feeding recommendations for breast and complementary feeding. The growth of these children was considered to represent optimal growth. Although the children were selected in a different fashion than for other national and international references, the WHO charts are constructed along similar lines to other charts and consist of descriptive percentiles from this select population.
Reference sets of charts, such as the 1990 UK reference, the 2000 CDC Growth Charts, and the WHO charts, are intended for clinical use in monitoring children’s growth. The use of selected percentiles of such charts to define overweight and obesity is a secondary purpose.
There are also several sets of BMI reference data that are intended specifically to define childhood overweight rather than to be used for clinical monitoring of growth patterns. These include only a few cutoff values. One reference set of BMI values that has been widely used consists of sex specific smoothed 85th and 95th percentiles for single year of age from 6 to 19 y based on data from NHANES I (1971–1974) in the United States, developed by Must et al. (26
). In 1995, a WHO Expert Committee recommended the use of these reference values (27
). Although the 1995 Must et al. (26
) reference values were considered to represent the 85th and 95th percentiles of the distribution of BMI in NHANES I, in fact, because of some slight over-smoothing of the data for girls, the Must et al. (26
) values for the 85th percentile are systematically lower than the empirical 85th percentile from the same data set and are more similar to the 80th percentile than to the 85th (28
). As a result, when the Must et al. (26
) values are used, the prevalence of BMI above the 85th percentile tends to be high for adolescent girls.
In 2000, Cole et al. (4
) published a set of smoothed sex specific BMI cutoff values based on 6 representative data sets from Brazil, Great Britain, Hong Kong, the Netherlands, Singapore, and the United States. The U.S. data used were the same as those from which the 2000 CDC growth charts were derived, excluding NHANES III data. The selection of data sets was based on specified criteria, including a large nationally representative sample, minimum age ranges of 6–18 y and appropriate quality control. These values, often referred to as the IOTF cutoff values, represent cutoff points chosen as the percentiles that matched the adult cutoffs of a BMI of 25 and 30 at age 18 y.
The Cole (4
) (IOTF) reference grew out of a workshop held by the IOTF and was developed to provide a suggested common basis for prevalence estimates internationally. The goal was to develop BMI criteria that could be used for international comparisons of prevalence without depending on using solely U.S. reference data and without using a specified percentile, such as the 85th or 95th percentile, of a specific population. The IOTF cutoffs were not intended as clinical definitions or to replace national reference data, but rather to provide a common set of definitions that researchers and policy makers in different countries could use internationally for descriptive and comparative purposes. Several discussions on the use of national compared with international reference data have been published (29