Investigation of the Relationship of Vitamin D, Parathyroid Hormone, Calcium Serum Level, and Insulin Resistance among Obese Individuals

Objective: Several studies have shown that 25-hydroxyvitamin D, parathyroid hormone (PTH), and serum calcium (Ca) may play functional roles with insulin resistance. Methods: This case-control study included 60 obese individuals with impaired fasting glucose who were compared with 60 nonobese individuals with normal fasting glucose who visited the endocrinology and metabolism department. Fasting plasma glucose, fasting insulin, triglyceride, PTH, and serum 25-hydroxyvitamin D (25(OH)D) were measured from all subjects in the morning after approximately 8 h of fasting using methods with respect to the standard operating procedures. Homeostatic model assessment of insulin resistance (HOMA-IR) was used for determining insulin resistance. The statistical analysis was attained by SPSS. Results: A lack of association was found between serum 25(OH)D and insulin resistance (HOMA-IR) before and after adjusting PTH, Ca, and various variables either in all participants or after exclusion of participants with HOMA-IR <= 2.5. On the other hand, PTH showed a significant inverse correlation with fasting insulin (p=0.022) and HOMA-IR (p=0.023) after adjusting 25(OH)D, serum Ca, and various variables and exclusion of participants with HOMA-IR <= 2.5. Conclusion: In the present study, we did not find a relationship between insulin resistance and vitamin D levels. Further studies are needed for clarifying the relationship between insulin resistance and vitamin D levels.