title: Vitamin D levels in a large Mediterranean cohort: reconsidering normal cut-off values.
abstract: OBJECTIVE
  The determination of the normal range of 25-hydroxyvitamin D [25-(OH)D], though currently based on suppression of PTH levels, still remains a controversial issue. The 25-(OH)D levels exhibit gender and seasonal variability, the latter attributed in part to changes of insolation.
  
  
  METHODS
  The aim of this cross-sectional study was to estimate the levels of 25-(OH)D on the island of Crete and their correlation with metabolic, hormonal and bone turnover parameters. The study was performed over a period of five years and involved 8,183 male and female individuals (8,042 analyzed).
  
  
  RESULTS
  Our results are as follows: (1) 25-(OH)D was significantly lower than expected (19.48±9.51 and 18.01±9.01 (ng/mL+SD) in males and females, respectively); (2) seasonal variation of 25-(OH)D was observed in both sexes (females < males), with values peaking in August; (3) a decline of 25-(OH)D was evident with advancing age, with lower levels in females compared to males up to menopause and no apparent difference between the genders thereafter; (4) levels of 25-(OH)D were lower in renal function impairment, diabetes/insulin resistance and inflammation, while no correlation was detectable in thyroid dysfunction; (5) normalization of PTH levels was observed at ~20 ng/mL 25-(OH)D. At the same cut-off level, a significant decrease of all measured bone turnover indices (b-ALP, osteocalcin and CTX) was evident.
  
  
  CONCLUSIONS
  Based on the above data, it appears that a cut-off level of 25-(OH)D close to 20 ng/mL better reflects the physiology of our population.
authors.affiliation: Laboratory of Clinical Chemistry-Biochemistry, University Hospital of Heraklion, P.O. Box 1352, Heraklion, 71110, Greece.
authors.forename: Marianna
authors.initials: M
authors.lastname: Katrinaki
authors.affiliation: Laboratory of Experimental Endocrinology-Clinical Immunology, University Hospital, Heraklion, Crete, Greece.|Laboratory of Experimental Endocrinology-Clinical Immunology, University of Crete, School of Medicine, Heraklion, Crete, Greece.
authors.forename: Marilena
authors.initials: M
authors.lastname: Kampa
authors.affiliation: Laboratory of Clinical Chemistry-Biochemistry, University Hospital of Heraklion, P.O. Box 1352, Heraklion, 71110, Greece.|Laboratory of Clinical Chemistry, University of Crete, School of Medicine, Heraklion, Crete, Greece.
authors.forename: Andrew
authors.initials: A
authors.lastname: Margioris
authors.affiliation: Laboratory of Experimental Endocrinology-Clinical Immunology, University Hospital, Heraklion, Crete, Greece.|Laboratory of Experimental Endocrinology-Clinical Immunology, University of Crete, School of Medicine, Heraklion, Crete, Greece.
authors.forename: Elias
authors.initials: E
authors.lastname: Castanas
authors.affiliation: Laboratory of Clinical Chemistry-Biochemistry, University Hospital of Heraklion, P.O. Box 1352, Heraklion, 71110, Greece. nmalliaraki@pagni.gr.
authors.forename: Niki
authors.initials: N
authors.lastname: Malliaraki
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D015415:Biomarkers / Q000097:blood; D016723:Bone Remodeling; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006115:Greece; D006304:Health Status; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D011237:Predictive Value of Tests; D012016:Reference Values; D015203:Reproducibility of Results; D012621:Seasons; D012737:Sex Factors; D013997:Time Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000175:diagnosis; D055815:Young Adult
chemical_list: D015415:Biomarkers; C470125:PTH protein, human; D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D