The authors set the context for this study in terms of the worldwide increase in obesity-related chronic health conditions, including in children. They cite the importance of identifying risk factors that contribute to obesity and that can be mitigated by policy changes and treatments. They specifically selected Vitamin D insufficiency as a possible risk factor for childhood obesity. Vitamin D is essential for calcium absorption and may be important for numerous other bodily processes. Vitamin D is primarily produced in the skin after exposure to sunlight. They note that while previous studies have found that vitamin D deficiency might be a risk factor for childhood obesity, they indicate that these studies have been limited because they have examined this relationship at one point in time (a cross-sectional design) and thus causality could not be determined. The major purpose of this study by Gilbert-Diamond and colleagues was to investigate the relationship between vitamin D levels and various indicators of obesity over a three-year period.
The researchers engaged a representative sample of nearly 500 low- and middle-income school-age children (5-12 years of age) from Bogota, Columbia. To examine this relationship, researchers collected a baseline blood sample from each child and various body measurements (e.g., height, weight, skinfold thickness, and waist circumference), and had parents complete a socio-demographic survey. Researchers collected body measurements from children each year for three years.
Gilbert-Diamond and colleagues found that 11% of children were overweight, 10.2% were vitamin D deficient, and 46.4% were vitamin D insufficient. In examining the relationship between vitamin D levels and obesity measures, researchers found that vitamin D deficient children had a greater increase in body mass index over time as compared to vitamin D sufficient children. Researchers also found that vitamin D deficient children had a greater increase in their skinfold-thickness ratio and waist circumference, as compared to vitamin D sufficient children. In addition, Gilbert-Diamond and colleagues examined the relationship between vitamin D levels and children's linear growth (i.e., height). In examining the data, researchers found that vitamin D deficient girls had slower linear growth than vitamin D sufficient girls.
The researchers' assessment of body measurements over time and use of a large, representative sample provides a valuable contribution to the literature and our understanding of the relationship between vitamin D levels and obesity.
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