Background: Rates of obesity and overweight are increasing dramatically worldwide in both developing and industrialized countries. Deficiencies of vitamins and minerals are prevalent among overweight and obese individuals across different socioeconomic strata. Previous studies suggest that the deficiency of some micronutrients may be underlying factors associated with increased body fat deposition. Micronutrient deficiencies may be a contributing factor in the development of greater adiposity in children which then can lead to a greater risk of obesity in adulthood. Deficiencies in growth-limiting micronutrients play important roles in determining linear growth and childhood stunting. Children who are stunted as result of underlying micronutrient deficiencies are at a higher risk of developing greater adiposity. Mexican American children have a high prevalence of overweight/obesity and are also more likely to be stunted.
Aims: The overall aim of this study is to investigate the relationships between selected micronutrient status and adiposity among Mexican American children and to assess whether stunted children are at an increased risk of greater adiposity compared to non-stunted children.
Methods: The analyses was limited to Mexican American children aged 8–15 years (n=1,131) using data from the US National Health and Nutrition Examination Survey (NHANES) 2001–2004. Body mass index (BMI (kg/m2)), truncal fat mass (TrFM), percentage of truncal fat (%TrFat), total body fat mass (TBFM), and percentage of total body fat (%TBF) were used as a measures of body adiposity for the main outcomes. Micronutrient concentrations included red blood cell (RBC) folate, serum folate, vitamin B12, vitamin D, α-carotene, β-carotene, retinol, and α-tocopherol. Serum α-tocopherol concentration was adjusted for serum total cholesterol concentrations. Stunting status was defined as height-for-age Z-score <–1.5 SD (according to National Center for Health Statistics Standards). BMI levels were classified using age- and gender-specific BMI percentiles from the CDC 2000. Multiple imputations of missing values for all covariates were made. The associations between micronutrient concentrations and body adiposity were determined using linear, multinomial and quantile regression models under the multiple imputation command that accommodates sample weight. In the multivariate models, the associations between micronutrient concentrations and body adiposity were adjusted for age, gender, poverty income ratio, stunting status, serum C-reactive protein concentrations, sedentary activities and supplement use.
Results: The prevalence of overweight and obesity were high, regardless of the different classification of body mass index used. Although the prevalence of overweight and obesity in 2001–2004 was high (20.42% and 22.42% respectively), the children were not severely obese with an average BMI of 21.74 (SD 5.47) and the average BMI-for-age Z-score was 0.73 (SD 1.09). The prevalence of underweight and stunting was low in this study population. Serum concentrations of vitamin B12, folate, vitamin D, α-carotene, trans-β-carotene, cis-β-carotene, and α-tocopherol adjusted for total cholesterol ratio, were found to be inversely associated with BMI, TrFat and TBF. Serum concentrations of retinol were positively associated with adiposity measures. Folate concentrations in red blood cells were observed to be positively correlated with %TrFat and %TBF, but did not show any significant associations with other adiposity measures. Stunting was more likely to be associated with older age, being female and/or having a low family socioeconomic status (poverty income ratio below thresholds). No differences in associations between micronutrient deficiencies and greater adiposity or fat mass were found between stunted children and non-stunted children. Macronutrient dietary intakes did not show positive association with body adiposity with the exception for protein intakes and percentage of energy intake from protein. Intakes of specific micronutrients investigated in this study showed different directions in their associations with adiposity. Intakes of calcium, folate, thiamine and riboflavin were inversely associated with adiposity; whereas intakes of vitamin A, retinol, α-carotene, β-carotene, vitamin C, zinc and selenium, showed positive associations with these measures.
Conclusion and Recommendation: Micronutrient deficiencies may be important in determining body adiposity which may in turn, be a determinant for obesity. However, it remains unclear whether this association represents a causal relationship and, if so, the direction of causality. Future research is needed to understand the causes and consequences of micronutrient status on adiposity and comorbidities. It is important that the effect of supplementation with multiple micronutrients on adiposity among children and adolescents with a high prevalence of micronutrient deficiencies be addressed through randomized micronutrient supplementation which will more effectively establish causality.