In a recent study published in the Metabolites Journal, researchers investigated the correlation between vitamin D deficiency and metabolic syndrome (MetS) components.
Study: Vitamin D Deficiency in Obese Children Is Associated with Some Metabolic Syndrome Components, but Not with Metabolic Syndrome Itself. Image Credit: FotoHelin/Shutterstock.com
Background
Vitamin D, important in various biological processes, is synthesized as cholecalciferol (vitamin D3) in skin exposed to ultraviolet B (UVB) light and converted into its active form, calcitriol, in the liver and kidneys.
Deficiency, often due to insufficient sunlight exposure or diet, or renal or hepatic issues, can lead to skeletal problems. The MetS, a cluster of risk factors including insulin resistance, elevated blood glucose, dyslipidemia, hypertension, and increased waist circumference, augments the risk of cardiovascular diseases and type 2 diabetes.
Emerging research suggests an association between MetS, obesity-related conditions, and vitamin D deficiency. Vitamin D affects glucose metabolism, insulin resistance, and inflammation, exhibiting correlations with hormones like leptin and adiponectin.
Consequently, low vitamin D may foster cardiovascular diseases by influencing adipokine levels.
About the study
The present study included 79 children suffering from obesity, aged 14.18 ± 2.67 years on average, excluding those with endocrine-related obesity or on medication that impacts metabolic or vitamin D and calcium metabolism.
Participants were evaluated based on body mass index (BMI)-z score, fat-free mass (FFM%), fat percentage (FAT%), and severe obesity (severe ob) using the International Obesity Task Force's BMI cut-off tables.
The severe ob criteria was a BMI equal to an adult's BMI of 35.0. Waist-to-height ratio (W/HtR) and waist-to-hip ratio (WHR) were calculated for all but one participant, and predicted muscle mass (PMM%) was assessed for 70 individuals through bioelectrical impedance analysis.
Venous blood samples were collected for standard metabolic biochemical markers and 25-hydroxyvitamin D (25OHD), a vitamin D marker, using enzyme-linked immunosorbent assay (ELISA) kits. The fresh blood samples were processed within an hour of collection, and the resulting serum was frozen at -20 °C for preservation.
Data analysis was done using STATISTICA software, with comparisons made between Vitamin D deficient (VDD) and Vitamin D sufficient (VDS) groups, as well as MetS-affected and unaffected groups, based on anthropometric and biochemical parameters.
The student's t-test was employed for inter-group comparisons. The Kolmogorov-Smirnov test was used for variance equality analysis and Pearson's correlation coefficient measured correlations. The significance threshold was set at a p-value of <0.05.
The study was sanctioned by the Ethics Committee of the Medical University of Silesia (Approval No. KNW/0022/KB1/131/15), and every participant and their caregivers gave informed consent. The study also adhered to the Helsinki Declaration's patient rights.
Study results
The present study group comprised 35 males and 44 females, averaging 14.18 ± 2.67 years. Despite no significant difference in BMI-z across groups, those in the VDD cohort exhibited a higher W/HtR, a significant MetS measure.
A negative correlation was found between W/HtR and 25OHD levels. Age showed significant variation between groups; vitamin D levels were noticeably higher in females.
Vitamin D (25OHD) levels differentiated the groups significantly, with the VDD group having deficient mean levels (12.66 ± 4.76), while the VDS group's mean levels were suboptimal (27.78 ± 5.59).
Discrepancies in lipid metabolism were observed, with the VDD group displaying lower high-density lipoprotein (HDL) and higher triglyceride (TG) levels than the VDS group, suggesting dyslipidemia risk.
There was no significant variance between groups regarding glucose metabolism and insulin resistance, including glucose and insulin levels at 0 and 120 minutes of oral glucose tolerance test (OGTT) and homeostasis model assessment of insulin resistance (HOMA-IR) scores.
However, a significant negative correlation between 25OHD and glucose at 120 minutes (glu120) was noted.
The participants were further categorized based on their MetS diagnosis, with 33 diagnosed and 45 not. Twelve met only one MetS criterion; the majority had two, while 16 and 17 met three or four MetS criteria, respectively.
While vitamin D levels were not significantly different between the non-MetS and MetS groups, the variances of this parameter were significant, with mean levels in the deficient range for both.
Discussions
The present study examined obesity measures and MetS biomarkers in Polish pediatric groups differentiated by VDS. Significant differences were seen in the VDD group, with higher W/HtR and TG levels and lower HDL and adiponectin levels. Other parameters showed no significant variances.
The researchers found that inadequate 25OHD correlated with increased W/HtR, an obesity measure more significant than previous findings.
For lipid metabolism, VDD children presented distinctively lower HDL and higher TG levels. Low HDL values are linked to cardiovascular diseases and type 2 diabetes. Despite inconclusive prior studies, this research found a significant difference in HDL levels between VDD and VDS groups.
The present study noted atherogenic dyslipidemia, represented by low HDL and high TG levels, was connected to atherosclerosis and insulin resistance. Elevated TG levels were seen in VDD children, with the difference more pronounced than in several other studies.
Lower adiponectin levels, common in obesity, were detected in the VDD group. Adiponectin, part of the MetS, has been associated with insulin resistance and type 2 diabetes, though the results are mixed. The VDD and VDS groups had no significant variance in the leptin/adiponectin ratio, an insulin resistance measure.
While no glucose metabolism-related parameters significantly differed between VDD and VDS groups, the correlation between 25OHD and glu120 levels suggested that vitamin D deficiency could impact glucose metabolism.
Despite non-significant differences in MetS severity between VDD and VDS groups, the study showed distinct differences in MetS components. Despite these altered components, all children presented with vitamin D deficiency.
Therefore, children with low vitamin D levels showed multiple metabolic disorders that, if unchecked, could lead to severe complications, like cardiovascular risk.
The researchers assert this study's uniqueness in examining the links between vitamin D deficiency and MetS components in Polish children while comparing findings from other global regions.
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