L Naga Rajeev

BACKGROUND: Thinness at <5 years of age, also known as wasting, is used to assess the nutritional status of populations for programmatic purposes. Thinness may be defined when either weight-for-height or body-mass-index-for-age (BMI-for-age) are below -2 SD of the respective World Health Organization standards. These definitions were compared for quantifying the burden of thinness. METHODS: Theoretical consequences of ignoring age were evaluated by comparing, at varying height-for-age z-scores, the age- and sex-specific cut-offs of BMI that would define thinness with these two metrics. Thinness prevalence was then compared in simulated populations (short, intermediate and tall) and real-life data sets from research and the National Family Health Survey-4 (NFHS-4) in India. RESULTS: In short (-2 SD) children, the BMI cut-offs with weight-for-height criteria were higher in comparison to BMI-for-age after 1 year of age but lower at earlier ages. In Indian research and NFHS-4 data sets (short populations), thinness prevalence with weight-for-height was lower from 0.5 to 1 years but higher at subsequent ages. The absolute difference (weight-for-height - BMI-for-age) for 0.5-5 years was 4.6% (15.9-11.3%) and 2.2% (19.2-17.0%), respectively; this attenuated in the 0-5 years age group. The discrepancy was higher in boys and maximal for stunted children, reducing with increasing stature. In simulated data sets from intermediate and tall populations, there were no meaningful differences. CONCLUSIONS: The two definitions produce cut-offs, and hence estimates of thinness, that differ with the age, sex and height of children. The relative invariance, with age and stature, of the BMI-for-age thinness definition favours its use as the preferred index for programmatic purposes.

INTRODUCTION: Prevalence of undernutrition continues to be high in India and low household wealth is consistently associated with undernutrition. This association could be modified through improved dietary intake, including dairy consumption in young children. The beneficial effect of dairy on child growth has not been explored at a national level in India. The present analyses aimed to evaluate the direct and indirect (modifying association of household level per adult female equivalent milk and milk product consumption) associations between household wealth index on height for age (HAZ) and weight for age (WAZ) in 6-59 months old Indian children using data from of nationally representative surveys. METHODS: Two triangulated datasets of two rounds of National Family Health Survey, (NFHS-3 and 4) and food expenditure (National Sample Survey, NSS61 and 68) surveys, were produced by statistical matching of households using Non-Iterative Bayesian Approach to Statistical Matching technique. A Directed Acyclic Graph was constructed to map the pathways in the relationship of household wealth with HAZ and WAZ based on literature. The direct association of wealth index and its indirect association through per adult female equivalent dairy consumption on HAZ and WAZ were estimated using separate path models for each round of the surveys. RESULTS: : 0.102; 95%CI: 0.093, 0.11). Adult female equivalent milk intake (increase of 10gm/day) was associated with higher HAZ (β_NFHS-3=0.001;95% CI: 0, 0.002; β_NFHS-4=0.002;95% CI: 0.002, 0.003) but had no association with WAZ. The indirect association of wealth with HAZ through dairy consumption was 2-fold higher in NFHS-4 compared to NFHS-3. CONCLUSIONS: The analysis of triangulated survey data shows that household level per- adult female equivalent dairy consumption positively modified the association between wealth index and HAZ, suggesting that regular inclusion of milk and milk products in the diets of children from households across all wealth quintiles could improve linear growth in this population.

Thinness and overweight/obese can be recognised by using either of the two anthropometric indices: (i) weight-for-height or (ii) body-mass-index (BMI)-for-age with abnormalities below −2 SD; above 2 SD and 3 SD of the respective World Health Organization (WHO) growth standards.1, 2 While weight-for-height has traditionally been utilised as a primary indicator of thinness and overweight/obesity, BMI-for-age offers a more comprehensive and accurate assessment, particularly for children under 5 years. Weight-for-height has limitations in assessing thinness in children. This metric does not consider growth and developmental changes that occur during childhood, leading to potential misclassification of individuals; weight-for-height does not differentiate between fat mass and lean body mass and disregards the age-related physiological changes in BMI making it less specific for identifying thinness or overweight/obese.2, 3 In contrast, BMI-for-age considers weight, height and age, offering a comprehensive measure of thinness. Based on population data, it allows comparison with peers of the same age and sex, adjusting for growth patterns and age-related BMI changes, making it valuable for assessing thinness in children and adolescents. BMI-for-age was prioritised over weight-for-height to identify thinness and overnutrition in children. According to hypothetical considerations from the National Centre for Health Statistics (NCHS), US standards, the weight/height2 metric must be used instead of the weight-for-height in under-five children.4 Using the latter metric could lead to potentially misleading assessments when evaluating extremely tall or short subjects. Based on NCHS growth charts, in children, the weight-for-height metric had a higher probability (0.9%–5%) of being categorised as thin (<10th percentile), and the disparities were more noticeable in shorter children.5 Few studies from high-income countries have partially explored this possibility after introducing WHO growth charts, concluding that BMI-for-age z-scores (BMIZ) is a better metric for estimating thinness and overnutrition prevalence in children under 5 years.6, 7 Data from the USA suggest that early childhood obesity is more strongly correlated with high BMI than high Weight-for-Length since 47% of infants with a BMI ≥97.7 percentile at 2 months of age were obese by the time they were 2 years old.8 However, the US cohort found that having a BMI ≥85 percentile when a child increases the risk of severe obesity by 2.5 times and clinical obesity by 3 times by the time the child is 6 years old.9 Another study indicates that the changes in BMIZ are better indicators of adiposity at 1-month age.10 Weight-for-height and BMI-for-age definitions provide varying estimates of thinness and overnutrition based on the height, sex and age of children, as shown by recent thorough analyses from India. Thinness estimates were higher with the weight-for-height criterion and lower for overnutrition in populations with significant stunting, especially in children aged 6–59 months. Since BMI provides a consistent metric from birth to adulthood and is less affected by age and stature, it is preferred for classifying thinness and overnutrition in children under 5.11 In conclusion, BMI-for-age provides a more accurate assessment of thinness in children than weight-for-height. Using BMI-for-age in clinical practice and public health can improve the identification and management of thinness and weight-related issues among youth. We urge health-care professionals and policymakers to consider BMI-for-age as the primary metric for estimating thinness, ensuring better health outcomes for children and adolescents.