Growth and overweight of Navajo youth: secular changes from 1955 to 1997

OBJECTIVE: To examine the growth status, prevalence of risk of overweight a nd of overweight, and secular changes in growth status in Navajo youth from 1955 to 1997. SUBJECTS: 526 (256 males, 270 females) Navajo children 6-12y of age. MEASUREMENTS: Stature and mass were measured and the body mass index (BMI) was calculated. ANALYSIS: All three variables were plotted relative to age- and sex-specifi c US reference data and the prevalence rates for risk of overweight and of overweight were estimated using the BMI as the criterion. The cut-off for t he risk of overweight was the age- and sex-specific 85th and 95th percentil es of NHANES I, while the cut-off for overweight was a BMI greater than or equal to 95th percentiles. Age-specific sex differences were compared using independent samples t-tests, Secular changes for body size were estimated by comparing age- and sex-specific means for stature, mass, and the BMI in the present study and two previous studies in 1955 and 1989, RESULTS: No statistically significant differences were observed between sex es within age groups. In both sexes, mean age-specific stature appeared to be relatively stable around the 50th percentile of US reference values. Mea n age-specific mass appeared to be relatively stable between the 50th and 9 0th percentiles of the reference values, while the mean BMI tended to fluct uate about the 85th percentile. Approximately 41% of the Navajo boys and gi rls 6-12y of age had BMIs greater than or equal to 85th percentiles of US r eference data. Compared to corresponding data on Navajo youth in 1955 and 1 989, the current sample was larger in mass and the BMI, The estimated rate of secular change in mass was about 1.5 kg/decade in younger boys and girls , and about 3 kg/decade in older boys and girls between 1955 and 1997, The estimated rate of secular change in the BMI was about 0.5-1.0 units/decade between 1955 and 1997, while that for stature was about 2 cm/decade between 1955 and 1997. CONCLUSIONS: The results are consistent with recent findings on the Navajo Health and Nutrition Survey that overweight is a serious public health conc ern across the lifespan in the Navajo, and that the problem begins in child hood, Furthermore, Navajo children appear to be heavier than about a decade ago.