Serum 25-hydroxyvitamin D is associated with insulin resistance independently of obesity in children ages 5-17

Serum vitamin D and obesity among US adolescents, NHANES 2011-2018

Background and objectives

Childhood obesity is highly prevalent worldwide. We aimed to assess whether serum 25-hydroxyvitamin D was associated with general/central obesity among US adolescents, and further to explore the mediatory impact of homeostasis model assessment of insulin resistance (HOMA-IR) on this association.

Methods

This study is cross-sectional in design. Study adolescents were enrolled from the National Health and Nutrition Examination Survey (NHANES), 2011-2018. Serum 25-hydroxyvitamin D categories associated with general (indexed by body mass index) and central (indexed by waist circumference to height ratio) obesity were regressed. The possible mediatory effect of HOMA-IR on this association was explored. The nonlinear and dose-response association was examined by restricted cubic spline (RCS) test.

Results

Total 2,696 adolescents were eligible for inclusion, and the mean age of all adolescents was 15.4 years. Overall, the percentage of general and central obesity was 38.0% and 38.6%, respectively. Compared with adolescents with sufficient vitamin D, adolescent with deficient and insufficient vitamin D intake were associated with general obesity and central obesity; fully-adjusted OR for general obesity was 1.602 (95% CI: 1.161-2.211) and 1.659 (1.385-1.986), and fully-adjusted OR for central obesity was 2.025 (1.445-2.837) and 1.557 (1.287-1.884), respectively, while there was no observable significance in adolescents with possibly harmful vitamin D. The proportion mediated by HOMA-IR was estimated to be 31.7% for global obesity and 50.3% for central obesity (both P < 0.05). More stratified analyses were presented, and identified that the association with general obesity was particularly present among Mexican American, while with central obesity among Non-Hispanic Black adolescents.

Conclusions

Our findings indicate that deficient or insufficient 25-hydroxyvitamin D concentrations were associated with the significant risk of general and central obesity among US adolescents, and approximately 30% and 50%, respectively, of these associations were mediated by HOMA-IR.

The Relationship between Anthropometric Measurements and Vitamin D Levels and Insulin Resistance in Obese Children and Adolescents

Objective: Our investigation aimed to determine the effect of vitamin D levels on the development of insulin resistance in obese adolescents and children and the influences of anthropometric measurements on predicting the development of insulin resistance. Materials and Methods: In this study, demographic data, laboratory findings, and anthropometric measurements of 150 adolescents and children that had obesity diagnoses between May 2021 and September 2022 were evaluated retrospectively. Those with and without insulin resistance were studied with regard to vitamin D levels, biochemical parameters, and anthropometric measurements. Three groups of patients were created: those with low levels of vitamin D (<20 ng/mL), those with insufficient levels (20−30 ng/mL), and those having normal levels (≥30 ng/mL). Groups were compared in terms of homeostatic model score (HOMA-IR) and anthropometric measurements. Correlation analysis was carried out to ascertain the correlation of anthropometric measurements with HOMA-IR. To ascertain the cutoff, specificity, and sensitivity values of anthropometric parameters in predicting insulin resistance in patients, receiver operating characteristic (ROC) analysis was carried out. Results: Vitamin D levels of obese adolescents and children with insulin resistance were substantially lower than those without insulin resistance (p < 0.001). As the vitamin D level increased, all anthropometric measurements except for the body fat percentage decreased significantly with the HOMA-IR score (p < 0.05). HOMA-IR demonstrated a strong positive relation with waist circumference (rs = 0.726, p < 0.001). Waist circumference had high specificity and sensitivity in predicting insulin resistance (87.3% and 87.4%, respectively). Conclusions: A significant relationship was observed between insulin resistance development and low levels of vitamin D in obese children and adolescents. As vitamin D levels increase, anthropometric measurements are more stable and do not increase. Waist circumference is the most effective anthropometric measurement for predicting the development of insulin resistance in obese adolescents and children.

A comprehensive look into the association of vitamin D levels and vitamin D receptor gene polymorphism with obesity in children

Childhood obesity accounts for several psychosocial and clinical consequences. Psychosocial consequences include lower self-esteem, social isolation, poor academic achievement, peer problems, and depression, whereas clinical consequences are cardiovascular diseases, type 2 diabetes, dyslipidemia, cancer, autoimmune diseases, girls early polycystic ovarian syndrome (PCOS), asthma, bone deformities, etc. A growing number of studies have uncovered the association of childhood obesity and its consequences with vitamin-D (vit-D) deficiency and vitamin-D receptor (VDR) gene polymorphisms such as single nucleotide polymorphisms (SNPs), e.g., TaqI, BsmI, ApaI, FokI, and Cdx2. Considering the impact of vit-D deficiency and VDR gene polymorphisms, identifying associated factors and risk groups linked to lower serum vit-D levels and prevention of obesity-related syndromes in children is of utmost importance. Previously published review articles mainly focused on the association of vit-D deficiency with obesity or other non-communicable diseases in children. The nature of the correlation between vit-D deficiency and VDR gene polymorphisms with obesity in children is yet to be clarified. Therefore, this review attempts to delineate the association of obesity with these two factors by identifying the molecular mechanism of the relationship.

Paraventricular Vitamin D Receptors Are Required for Glucose Tolerance in Males but Not Females

When delivered directly into the brain, vitamin D, can improve glucose levels in male mice. Additionally, the loss of the vitamin D receptor (VDR) in male mice's paraventricular hypothalamus (PVH) results in impaired glucose tolerance. Data in humans shows that low vitamin D levels are detrimental to glucose homeostasis, an effect that may be more prominent in men. However, it is unknown if vitamin D action in the brain is required for normal glucose regulation in female mice. This study shows that in both viral and genetic models, male mice with obesity and PVH VDR loss have impaired glucose tolerance while female mice are unaffected. Weights were unaltered in both sexes by PVH VDR loss. Additionally, PVH VDR loss did not cause any glucose abnormalities in either sex when the mice were on a chow diet. Utilizing electrophysiology studies, we show PVH VDR loss resulted in decreased baseline firing frequency and resting membrane potential in males, but not females. Additionally, male mice with PVH VDR loss had impaired miniature excitatory postsynaptic currents (mEPSC), while females were unaffected. Interestingly, the PVH neurons of both sexes were activated by exogenous vitamin D (1,25-dihydroxyvitamin D3), an effect dependent upon the VDR. Thus, there is sexual dimorphism, for the actions of the PVH VDR on glucose regulation. PVH VDRs are necessary for normal glucose homeostasis in males but not females and this may be secondary to actions of the VDR on neuronal activity.

The effect of pomegranate extract on anthropometric indices, serum lipids, glycemic indicators, and blood pressure in patients with nonalcoholic fatty liver disease: A randomized double-blind clinical trial

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. The beneficial effects of pomegranate have been shown on insulin resistance and obesity, which are linked to NAFLD pathogenesis. The aim of this study was to investigate the efficacy of pomegranate extract in patients with NAFLD. Forty-four NAFLD patients were randomly assigned to receive two pomegranate extract tablets or placebo for 12 weeks. Anthropometric measurements, serum lipids, glycemic indicators, and blood pressure were assessed at baseline and the end of the study. Pomegranate was associated with a reduction in the total cholesterol (p ˂ .001), triglyceride (p ˂ .001), low-density lipoprotein cholesterol (LDL-C)-to-high-density lipoprotein cholesterol (HDL-C) ratio (p ˂ .003), fasting blood sugar (p ˂ .001), homeostatic model assessment of insulin resistance (p = .02), diastolic blood pressure (p = .04), weight (p ˂ .001), body mass index (p ˂ .001), and waist circumference (p = .002), as compared to placebo. A significant increase was observed in serum HDL-C (p ˂ .001) after intervention with the pomegranate extract. However, no significant difference was shown between the two groups in serum insulin and LDL-C. The pomegranate extract supplement could be used as a complementary therapy along with existing therapies to improve glycemic indicators, serum lipids, anthropometric indices, and blood pressure in patients with nonalcoholic fatty liver.

Investigation of Vitamin D Deficiency in Pre-School Children During Summer Season

Aim: Vitamin D deficiency is an important public health problem, especially affecting children. The aim of our study is to evaluate the serum 25 (OH) vitamin D levels of children during the summer and to determine some features such as exposure to the sun, oral vitamin D supplementation, and to examine the parameters that affect serum vitamin D levels. Methods: In our study, children aged between 12 and 83 months were included. A questionnaire was answered by families. In this cross-sectional study, serum 25 (OH) vitamin D levels of children and biochemical parameters were examined. Results: The mean serum 25 (OH) vitamin D level was 27.0±12.4 ng/ml. Vitamin D deficiency was found 17%, and vitamin D insufficiency was 6%. The children that taking daycare indoors and body mass index <5th percentile had lower serum 25 (OH) vitamin D levels. Children between the ages of 12- 36 months and children with chronic diseases were found to have a shorter time to benefit from sunlight. Conclusion: The rate of vitamin D deficiency and insufficiency (<20 ng/ml) in children were found at 23% in summer season. Families and caregivers should be informed about vitamin D and should be aware of safe sun exposure. Keywords: Vitamin D, sunlight, summer, children, vitamin D deficiency