title: Non-linear contribution of serum vitamin D to symptomatic diabetic neuropathy: A case-control study.
abstract: OBJECTIVE
  Vitamin D deficiency has recently been speculated to be associated with increased risk of diabetes neuropathy (DN). The aim of this study was to evaluate the odds of symptomatic DN across serum vitamin D levels.
  
  
  METHODS
  All patients with DM were assessed using diabetic neuropathy symptoms and diabetic neuropathy examination score. Overall, 150 cases with DN and 600 controls were included. Serum 25-hydroxyvitamin D (25-OH-D) was measured to determine vitamin D status.
  
  
  RESULTS
  A non-linear association between 25-OH-D and suffering from symptomatic DN was observed which was extracted after stratifying the ORs across different serum 25-OH-D levels. When compared to individuals with 25-OH-D of 30-40 ng/mL, patients with deficient (<20 ng/mL) vitamin D levels had higher odds of having symptomatic DN (OR: 2.04, 95%CI: 0.99-4.02, P=0.054). Participants with vitamin D values of greater than 40 ng/mL were also more likely to exhibit symptomatic DN (fully adjusted OR: 4.29, 95%CI: 1.59-11.55).
  
  
  CONCLUSIONS
  We hypothesize a non-linear contribution of serum vitamin D to symptomatic DN occurrence, which emphasizes that administration of vitamin D should be monitored and evaluated more carefully, especially in patients with diabetes.
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: esteghamati@tums.ac.ir.
authors.forename: Alireza
authors.initials: A
authors.lastname: Esteghamati
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: afotouhi@tums.ac.ir.
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran; Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: dehsarvi.sara@gmail.com.
authors.forename: Sara
authors.initials: S
authors.lastname: Faghihi-Kashani
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: nimahn@gmail.com.
authors.forename: Nima
authors.initials: N
authors.lastname: Hafezi-Nejad
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: bh.medstudent@gmail.com.
authors.forename: Behnam
authors.initials: B
authors.lastname: Heidari
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: Shbahaei@gmail.com.
authors.forename: Sara
authors.initials: S
authors.lastname: Sheikhbahaei
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: ali_zandieh3@yahoo.com.
authors.forename: Ali
authors.initials: A
authors.lastname: Zandieh
authors.affiliation: Endocrinology and Metabolism Research Center (EMRC), Tehran University of Medical Sciences (TUMS), Tehran, Iran. Electronic address: nakhjavanim@tums.ac.ir.
authors.forename: Manouchehr
authors.initials: M
authors.lastname: Nakhjavani
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003929:Diabetic Neuropathies / Q000097:blood* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007492:Iran / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D012307:Risk Factors; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology
chemical_list: D014807:Vitamin D
keywords: Diabetes mellitus; Diabetic neuropathy; Toxicity; Vitamin D