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

OBJECTIVE: To examine the growth status, prevalence of risk of overweight and of overweight, and secular changes in growth status in Navajo youth from 1955 to 1997. SUBJECTS: 526 (256 males, 270 females) Navajo children 6 ‐ 12 y 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-specific 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 the risk of overweight was the age- and sex-specific 85th and 95th percentiles of NHANES I, while the cut-off for overweight was a BMI 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 sexes within age groups. In both sexes, mean age-specific stature appeared to be relatively stable around the 50th percentile of US reference values. Mean age-specific mass appeared to be relatively stable between the 50th and 90th percentiles of the reference values, while the mean BMI tended to fluctuate about the 85th percentile. Approximately 41% of the Navajo boys and girls 6 ‐ 12 y of age had BMIs 85th percentiles of US reference data. Compared to corresponding data on Navajo youth in 1955 and 1989, 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 concern across the lifespan in the Navajo, and that the problem begins in childhood. Furthermore, Navajo children appear to be heavier than about a decade ago. InternationalJournal of Obesity (2000) 24, 211‐218