25-Hydroxyvitamin D Concentrations and In Vivo Insulin Sensitivity and β-Cell Function Relative to Insulin Sensitivity in Black and White Youth

Abstract

OBJECTIVETo examine the relationships between plasma 25-hydroxyvitamin D [25(OH)D] and in vivo insulin sensitivity and β-cell function relative to insulin sensitivity, disposition index (DI), in black and white youth.RESEARCH DESIGN AND METHODSPlasma 25(OH)D concentrations were analyzed in banked specimens in healthy youth aged 8 to 18 years who had existing data on hyperinsulinemic-euglycemic and hyperglycemic clamp to assess insulin sensitivity and secretion, and measurements of body composition, and abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT).RESULTSA total of 183 research volunteers (mean ± SD; age, 12.6 ± 2.2 years; 98 white, 98 male, 92 obese) were studied. Analysis of HbA1c, fasting glucose and insulin, insulin sensitivity, and DI across quartiles of plasma 25(OH)D revealed no differences among whites. In blacks, the observed significance of higher insulin sensitivity and DI in the highest quartile of 25(OH)D disappeared after adjusting for any of the adiposity measures (BMI or fat mass or VAT or SAT). The difference in insulin sensitivity (9.4 ± 1.2 vs. 5.6 ± 0.5 mg/kg/min per μU/mL; P = 0.006) between 25(OH)D nondeficient (≥20 ng/mL) versus deficient (<20 ng/mL) black youth also was negated when adjusted for adiposity.CONCLUSIONSIn healthy youth, plasma 25(OH)D concentrations bear no independent relationship to parameters of glucose homeostasis and in vivo insulin sensitivity and β-cell function relative to insulin sensitivity. It remains to be determined whether in youth with dysglycemia the relationships are different and whether vitamin D optimization enhances insulin sensitivity and β-cell function.

Inverse relationship between vitamin D status and insulin resistance and the risk of impaired fasting glucose in Korean children and adolescents: the Korean National Health and Nutrition Examination Survey (KNHANES) 2009–2010

“…The potential effects of VitD on glucose homeostasis are considered to be mediated by autocrine and paracrine functions involving the transcriptional regulation of genes in pancreatic b-cells, skeletal myocytes and immune cells, improving insulin secretion and sensitivity and reducing inflammation (13,16) . Despite theoretical links between VitD and insulin sensitivity and/or secretion, controversy remains regarding the relationship between 25(OH)D levels and surrogate indices of insulin sensitivity (4)(5)(6)(7)25,26) or b-cell function (7,25,26) and the risk of glucose intolerance or T2DM (6,9,27) . These discrepancies in the relationships between VitD status and outcomes related to glucose homeostasis in paediatric or adult populations may be attributable to differences in study sample size, participant characteristics (race, ethnicity and degree of obesity), method of measuring insulin sensitivity and/or b-cell function, and the adjusted markers of adiposity used.…”

“…We used HOMA-IR and QUICKI, reflecting only hepatic insulin sensitivity rather than in vivo whole-body insulin sensitivity, which encompasses both hepatic and peripheral tissues, measured using hyperinsulinaemic-euglycaemic and hyperglycaemic clamps. Rajakumar et al (26) recently reported that 25(OH)D levels are not independently related to in vivo insulin sensitivity or b-cell function, after adjustment for total body fat or visceral adipose tissue, in healthy black and white youth aged 8-18 years without dysglycaemia. Our study is the first to show that a low VitD status is significantly related to hepatic IR and IFG, independently of total body fat, in Korean adolescents.…”

PTH-Vitamin D-Glycemia Interactions Reloaded

“…Hypovitaminosis D is associated with obesity (2), and low vitamin D states predict higher fasting glycemia and insulin resistance in population studies (3,4), yet other studies showed no relations between vitamin D status and glucose homeostasis after adjusting for adiposity (5,6). Vitamin D supplementation has not consistently benefited glycemia in intervention trials despite adequate increments into a "normal range" (7).…”

The Ratio of Parathyroid Hormone to Vitamin D Is a Determinant of Cardiovascular Risk and Insulin Sensitivity in Adolescent Girls

“…Although our sample size is relatively small, some larger studies have similarly reported a lack of association between 25-OHD and glucose homeostasis, 5,14 arguing instead that apparent relationships are confounded by body fat, which demonstrates a strong inverse association with circulating 25-OHD. 13,14 Of note, associations of the ratio of PTH/25-OHD 17,23 with insulin measures were stronger than those of PTH alone within obese girls, suggesting a possibly additional, albeit minor, role of lower 25-OHD levels in driving these associations. Thus, further research is needed to investigate associations between 25-OHD and insulin sensitivity independent of fat stores across the weight spectrum.…”