Controversial Impact of Vitamin D Supplementation on Reducing Insulin Resistance and Prevention of Type 2 Diabetes in Patients with Prediabetes: A Systematic Review.

BACKGROUND: Prediabetes has become a worldwide health problem. Multiple clinical trials have been conducted to determine the potential benefits of vitamin D supplementation in preventing the conversion to diabetes, but the results are inconsistent. The aims of this study were to evaluate the current knowledge and to suggest recommendations for researchers on designing future trials regarding that matter. METHODS: Four databases were searched for randomized control trials from the last 10 years about vitamin D and insulin resistance. The systematic electronic literature search identified 2645 studies, of which thirty-eight qualified for full-text reading and discussion. Finally, eight trials were included. RESULTS: Final results of seven trials reported that supplementation of vitamin D does not reduce insulin resistance nor reduces the risk of diabetes mellitus type 2 development in prediabetes. Only one trial showed improvements in fasting glucose and HOMA-IR. CONCLUSIONS: Due to the great variation and biases in study designs, an unambiguous interpretation of the results is not possible. To eliminate those vulnerabilities in the future, we made certain suggestions for study design. Long-term and well-designed studies are still required.

Fitness, Food, and Biomarkers: Characterizing Body Composition in 19,634 Early Adolescents.

Adolescent obesity persists as a major concern, especially in Central and Eastern Europe, yet evidence gaps exist regarding the pivotal early adolescent years. Our objective was to provide a comprehensive picture using a holistic approach of measured anthropometry in early adolescence, including body composition, cardiorespiratory fitness (CRF), and reported lifestyle characteristics. We aimed to elucidate potential sex/gender differences throughout and associations to biomarkers of disease risk for obese adolescents. Methods: Trained nurses measured 19,634 early adolescents (12−14-year-olds), we collected parental reports, and, for obese adolescents, fasting blood samples in four major Polish cities using a cross-sectional developmental design. Results: 24.7% boys and 18.6% girls were overweight/obese, and 2886 had BMI ≥ 90th percentile. With increasing age, there was greater risk of obesity among boys (p for trend = 0.001) and a decreasing risk of thinness for girls (p for trend = 0.01). Contrary to debate, we found BMI (continuous) was a useful indicator of measured fat mass (FM). There were 38.6% with CRF in the range of poor/very poor and was accounted for primarily by FM in boys, rather than BMI, and systolic blood pressure in girls. Boys, in comparison to girls, engaged more in sports (t = 127.26, p < 0.0001) and consumed more fast food (t = 188.57, p < 0.0001) and sugar-sweetened beverages (167.46, p < 0.0001). Uric acid, a potential marker for prediabetes, was strongly related to BMI in the obese subsample for both boys and girls. Obese girls showed signs of undernutrition. Conclusion: these findings show that overweight/obesity is by far a larger public health problem than thinness in early adolescence and is characterized differentially by sex/gender. Moreover, poor CRF in this age, which may contribute to life course obesity and disease, highlights the need for integrated and personalized intervention strategies taking sex/gender into account.

Long-Term Effects of Vitamin D Supplementation in Obese Children During Integrated Weight-Loss Programme-A Double Blind Randomized Placebo-Controlled Trial.

BACKGROUND: Vitamin D was studied in regards to its possible impact on body mass reduction and metabolic changes in adults and children with obesity yet there were no studies assessing the impact of vitamin D supplementation during a weight management program in children and adolescence. The aim of our study was to assess the influence of 26 weeks of vitamin D supplementation in overweight and obese children undergoing an integrated 12-months' long weight loss program on body mass reduction, body composition and bone mineral density. METHODS: A double-blind randomized placebo-controlled trial. Vitamin D deficient patients (<30 ng/ml level of vitamin D) aged 6-14, participating in multidisciplinary weight management program were randomly allocated to receiving vitamin D (1200 IU) or placebo for the first 26 weeks of the intervention. RESULTS: Out of the 152 qualified patients, 109 (72%) completed a full cycle of four visits scheduled in the program. There were no difference in the level of BMI (body mass index) change - both raw BMI and BMI centiles. Although the reduction of BMI centiles was greater in the vitamin D vs. placebo group (-4.28 ± 8.43 vs. -2.53 ± 6.10) the difference was not statistically significant (p = 0.319). Similarly the reduction in fat mass-assessed both using bioimpedance and DEXa was achieved, yet the differences between the groups were not statistically significant. CONCLUSIONS: Our study ads substantial results to support the thesis on no effect of vitamin D supplementation on body weight reduction in children and adolescents with vitamin D insufficiency undergoing a weight management program.

Long-term effects of vitamin D supplementation in vitamin D deficient obese children participating in an integrated weight-loss programme (a double-blind placebo-controlled study) - rationale for the study design.

BACKGROUND: Obesity is associated not only with an array of metabolic disorders (e.g. insulin resistance, hiperinsulinemia, impaired tolerance of glucose, lipid disorders) but also skeletal and joint abnormalities. Recently, a pleiotropic role of vitamin D has been emphasized. Obese children frequently present with vitamin D deficiency, and greater fat mass is associated with lower serum concentration of this vitamin. Although some evidence suggests that weight loss may affect vitamin D status, this issue has not been studied extensively thus far. The aim of a double-blind placebo-controlled study is to assess long-term health effects of vitamin D supplementation in vitamin D deficient obese children participating in an integrated weight-loss programme. METHODS: A randomized double-blind, placebo-controlled trial analysing the effects of vitamin D3 supplementation in overweight or obese vitamin D deficient (<30 ng/ml) children participating in an integrated weight-loss programme. Children are randomized to receive either vitamin D (1200 IU) or placebo for 26 weeks. Primary endpoints include changes in BMI (body mass index), body composition and bone mineral density at the end of the study period, and secondary endpoints - the changes in laboratory parameter reflecting liver and kidney function (transaminases, creatinine) and glucose homeostasis (glucose and insulin levels during oral glucose tolerance test). DISCUSSION: The effects of vitamin D supplementation in obese individuals, especially children, subjected to a weight-loss program are still poorly understood. Considering physiological processes associated with puberty and adolescent growth, we speculate that supplementation may enhance weight reduction and prevent bone loss in obese children deficient in this vitamin. TRIAL REGISTRATION: NCT 02828228 ; Trial registration date: 8 Jun 2016; Registered in: ClinicalTrials.gov. The trial was registered retrospectively.