Association between insulin-like growth factor-1, measures of overnutrition and undernutrition and insulin resistance in black adolescents living in the North-West Province, South Africa

Association of Body Mass Index with Insulin-like Growth Factor-1 Levels among 3227 Chinese Children Aged 2-18 Years

OBJECTIVES

Insulin-like growth factor-1 (IGF-1) levels are affected by nutritional status, yet there is limited research exploring the association between body mass index (BMI) and IGF-1 levels among children.

METHODS

This cross-sectional study included 3227 children aged 2-18 years without specific diseases, whose height, weight, and pubertal stages were measured and assessed by pediatricians. BMI standard deviation scores (BMISDS) were used to categorize children as underweight (BMISDS < -2); normal-weight (-2 ≤ BMISDS ≤ 1); overweight (1 < BMISDS ≤ 2); and obese (BMISDS > 2). Children were divided into low-level (<-0.67 SD) and nonlow-level (≥-0.67 SD) groups based on IGF-1 standard deviation scores (IGF-1SDS). The association between IGF-1 and BMI as categorical and continuous variables was explored by Binary logistic regression, the restrictive cubic spline model, and the generalized additive model. Models were adjusted by height and pubertal development. Recursive algorithm and multivariate piecewise linear regression were further utilized to assess the threshold of the smooth curve.

RESULTS

IGF-1 levels varied by BMI categories, with the highest levels observed in the overweight group. The proportion of low IGF-1 levels in underweight, normal-weight, overweight, and obese groups was 32.1%, 14.2%, 8.4%, and 6.5%, respectively. The risk odds of low IGF-1 levels in underweight children were 2.86-, 2.20-, and 2.25-fold higher than in children with normal weight before adjustment, after adjustment for height, and after adjustment for height and puberty, respectively. When analyzing the association between BMI and low IGF-1 levels, dose-response analysis demonstrated an inverted J-shaped relationship between BMISDS and low IGF-1 levels. Lower or higher BMISDS increased the odds of low IGF-1 levels, and significance was retained in underweight children but not in obese children. When BMI and IGF-1 levels were used as continuous variables, the relationship between the BMISDS and IGF-1SDS followed a nonlinear inverted U shape. IGF-1SDS increased with the increase of BMISDS (β = 0.174, 95% CI: 0.141 to 0.208, p < 0.01) when BMISDS was less than 1.71 standard deviation (SD) and decreased with the increase of BMISDS (β = -0.358, 95% CI: -0.474 to -0.241, p < 0.01) when BMISDS was greater than 1.71 SD.

CONCLUSIONS

The relationship between BMI and IGF-1 levels was found to depend on the type of variable, and extremely low or high BMI values could result in a tendency toward low IGF-1 levels, emphasizing the importance of maintaining a normal BMI range for normal IGF-1 levels.

The challenges of underweight and overweight in South African children: are we winning or losing the battle? A systematic review

Underweight and overweight are adverse effects of malnutrition and both are associated with negative health consequences in children and adolescents. In South Africa, the burden of economic and social disparity coexists with malnutrition in children. The purpose of this study was to review available South Africa studies regarding the comprehensive summary of prevalence of underweight and overweight and evaluates government policies in addressing undernutrition and overnutrition in South African children and adolescents. We searched subject-specific electronic bibliographic databases of observational studies published on malnutrition, undernutrition, overnutrition, underweight and overweight in South African boys and girls from birth to 20 years of age in studies published on or after 1990. A total of sixteen cross-sectional, three longitudinal studies and one report met the criteria for inclusion in this review. Descriptive data synthesis revealed the small number of longitudinal studies highlights the dearth of research in tracking undernutrition and overnutrition in South African children. In this review, 0.7%-66% of underweight was reported among children in rural areas compared to a 3.1%-32.4% of overweight in urban areas. All studies reported a higher rate of underweight in boys than girls who were significantly more likely to have higher body fat. The data indicated that both underweight and overweight were positively related with health-related physical activity and psychological health problems such as low activity, low fitness, low self-image and self-esteem. Numerous recommendations were made in the reviewed studies, however effective strategic programs in eradicating both underweight and overweight are minimal. It is evident from the reviewed studies that the burden of underweight and overweight are still a problem in South African children. The most highly affected by underweight are rural children, while children in urban areas in transition are faced with burden of overweight. There is little evidence to suggest that government strategic programs are effective in addressing underweight and overweight in South African children. Based on these findings, sustainable school-based feeding schemes and physical education programmes are needed for optimal benefits in children and adolescents.