title: The ratio of parathyroid hormone to vitamin D is a determinant of cardiovascular risk and insulin sensitivity in adolescent girls.
abstract: BACKGROUND
  Vitamin D insufficiency and higher testosterone are common in obese girls and may adversely affect glucose homeostasis and cardiovascular risk. Data are conflicting regarding the impact of parathyroid hormone (PTH) on these factors. Our objective was to determine associations of 25-hydroxyvitamin D (25-OHD), PTH, and testosterone with measures of glucose homeostasis and cardiovascular risk in adolescent girls after controlling for regional adiposity, with the hypothesis that lower 25-OHD, a higher PTH or PTH/25-OHD ratio, and higher testosterone would be associated with lower insulin sensitivity and greater cardiovascular risk.
  
  
  METHODS
  A total of 15 obese girls and 15 matched normal weight controls (12-18 years) underwent fasting measurements of 25-OHD, PTH, testosterone, sex hormone-binding globulin (SHBG), high-sensitivity C-reactive protein (hsCRP), oral glucose tolerance testing, and quantification of visceral (VAT) and subcutaneous (SAT) fat by magnetic resonance imaging (MRI).
  
  
  RESULTS
  There were no associations of 25-OHD with measures of glucose homeostasis or hsCRP. In contrast, PTH and PTH/25-OHD were associated negatively with homeostasis model assessment of insulin resistance (HOMA-IR) and positively with quantitative insulin sensitivity check index (QUICKI) in obese girls but not controls. These associations remained significant after controlling for body mass index standard deviation score (BMI-SDS), but not for VAT. On regression modeling, PTH/25-OHD was positively associated with hsCRP after controlling for BMI-SDS or VAT. Free testosterone positively predicted the corrected insulin response.
  
  
  CONCLUSIONS
  In obese girls, PTH/25-OHD is positively associated with measures of insulin sensitivity and hsCRP. Further studies are needed to investigate the relationship between PTH and glucose homeostasis in obesity.
authors.affiliation: Neuroendocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
authors.forename: Takara
authors.initials: T
authors.lastname: Stanley
authors.forename: Miriam A
authors.initials: MA
authors.lastname: Bredella
authors.forename: Lisa
authors.initials: L
authors.lastname: Pierce
authors.forename: Madhusmita
authors.initials: M
authors.lastname: Misra
mesh_terms: D000293:Adolescent; D002097:C-Reactive Protein / Q000032:analysis; D002318:Cardiovascular Diseases / Q000097:blood / Q000453:epidemiology* / Q000378:metabolism; D016022:Case-Control Studies; D002648:Child; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D056865:Ideal Body Weight / Q000502:physiology; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology; D009765:Obesity / Q000097:blood / Q000453:epidemiology / Q000378:metabolism; D010281:Parathyroid Hormone / Q000097:blood*; D012307:Risk Factors; D014807:Vitamin D / Q000097:blood*
chemical_list: D007328:Insulin; D010281:Parathyroid Hormone; D014807:Vitamin D; D002097:C-Reactive Protein