The study of obese and non-obese children in the USA found that low vitamin D levels were significantly more prevalent in obese children – and were associated with risk factors for type 2 diabetes, including insulin resistance.
"Our study found that obese children with lower vitamin D levels had higher degrees of insulin resistance," said Dr Micah Olson of The University of Texas Southwestern Medical Center – the lead author of the study.
"Although our study cannot prove causation, it does suggest that low vitamin D levels may play a role in the development of type 2 diabetes," he added.
Writing in the Journal of Clinical Endocrinology & Metabolism, Olson and his team reported that lower levels of blood plasma 25-hydroxyvitamin D – 25(OH)D – in obese children were associated with reductions in models of insulin resistance including two hour glucose tolerance tests.
High rates of vitamin D deficiency have been found in obese populations and past studies have linked low vitamin D levels to cardiovascular disease and type 2 diabetes.
However, the authors noted that the mechanisms by which obesity and its related illnesses are related to vitamin D deficiency are not fully known.
The new study examined associations between vitamin D levels and dietary habits in obese children. Olson and his team tested for correlations between vitamin D levels and markers of abnormal glucose metabolism and blood pressure in a total of 498 obese and non-obese children from North Texas, USA.
The team measured plasma vitamin D levels, blood sugar levels, serum insulin, BMI and blood pressure, and participants were asked to provide dietary information – including daily intake of soda, juice and milk, average daily fruit and vegetable intake, and whether or not they routinely skipped breakfast.
The team found that 92% of obese subjects had a 25(OH)D level below the ‘adequate’ levels of 75 nmol per litre, whilst 50% were classed as deficient – with levels below 50 nmol per litre.
"Poor dietary habits such as skipping breakfast and increased soda and juice intake were [also] associated with the lower vitamin D levels seen in obese children," revealed Olson.
He said that future studies are needed to determine the clinical significance of lower vitamin D levels in obese children.
Olson added that future research should investigate the required amount and duration of ‘treatment’ necessary to replenish vitamin D levels in deficient children, and whether increasing vitamin D status “can improve primary clinical endpoints such as insulin resistance."
Source: The Journal of Clinical Endocrinology & Metabolism
Published online ahead of print, doi: 10.1210/jc.2011-1507
“Vitamin D Deficiency in Obese Children and Its Relationship to Glucose Homeostasis”
Authors: M.L. Olson, N.M. Maalouf, J.D. Oden, P.C. White, M.R. Hutchison