Vitamin D Status and Its Relation to Age and Body Mass IndexBischof M.G. · Heinze G. · Vierhapper H.
aDivision of Endocrinology and Metabolism, Department of Internal Medicine III, and bSection of Clinical Biometrics, Core Unit for Medical Statistics and Informatics, Medical University of Vienna, Vienna, Austria
Background/Aims: While numerous studies have examined 25(OH)-vitamin D3 (25-D) concentrations and their relation to parathyroid hormone (PTH) levels there is only limited information on the interrelation between 25-D, 1,25(OH)2-vitamin D3 (1,25-D) and PTH. It was the aim of this study to assess the vitamin D endocrine system and its relation to age and body mass index (BMI). Methods: This cross-sectional study comprised a convenience sample of 483 adults which attended the endocrinology outpatient service of a university hospital in the years 2002–2004. Results: The mean concentrations of 25-D, 1,25-D, calcium and PTH were 21.0 ± 10.6 ng/ml, 47.9 ± 21.7 pg/ml, 9.48 ± 0.48 mg/dl and 51.0 ± 27.2 pg/ml, respectively. 25-D was related (p < 0.01) to BMI, age, PTH and 1,25-D. After correction for 25-D, we found no relation between BMI and 1,25-D. PTH was related (p < 0.01) to serum calcium, BMI, age and 1,25-D (p = 0015). There was a seasonal variation in both, 25-D and 1,25-D serum concentrations: 25-D levels were lowest in January and increased until July while the nadir and zenith of 1,25-D were found in April and October, respectively. Conclusion: Since BMI was negatively related to 25-D the prevalence of 25-D deficiency (<8.8 ng/ml) increased from 8.8% in subjects with BMI <30 kg/m2 to 15.0% in subjects with BMI >30 kg/m2. BMI, age and season should be taken into account when assessing a patients vitamin D status and more aggressive vitamin D supplementation should be considered for obese subjects.