title: Vitamin D levels are associated with cardiac autonomic activity in healthy humans.
abstract: Vitamin D deficiency (≤50nmol/L 25-hydroxy vitamin D) is a cardiovascular (CV) risk factor that affects approximately one billion people worldwide, particularly those affected by chronic kidney disease (CKD). Individuals with CKD demonstrate abnormal cardiac autonomic nervous system activity, which has been linked to the significant rates of CV-related mortality in this population. Whether vitamin D deficiency has a direct association with regulation of cardiac autonomic activity has never been explored in humans.
  
  
  METHODS
  Thirty-four (34) healthy, normotensive subjects were studied and categorized based on 25-hydroxy vitamin D deficiency (deficient vs. non-deficient, n = 7 vs. 27), as well as 1,25-dihydroxy vitamin D levels (above vs. below 25th percentile, n = 8 vs. 26). Power spectral analysis of electrocardiogram recordings provided measures of cardiac autonomic activity across low frequency (LF) and high frequency (HF, representative of vagal contribution) bands, representative of the sympathetic and vagal limbs of the autonomic nervous system when transformed to normalized units (nu), respectively, as well as overall cardiosympathovagal balance (LF:HF) during graded angiotensin II (AngII) challenge (3 ng/kg/min × 30 min, 6 ng/kg/min × 30 min).
  
  
  RESULTS
  At baseline, significant suppression of sympathovagal balance was observed in the 25-hydroxy vitamin D-deficient participants (LF:HF, p = 0.02 vs. non-deficient), although no other differences were observed throughout AngII challenge. Participants in the lowest 1,25-dihydroxy VD quartile experienced significant withdrawal of inhibitory vagal control, as well as altered overall sympathovagal balance throughout AngII challenge (HF, mean difference = -6.98 ± 3 nu, p = 0.05; LF:HF, mean difference = 0.34 ± 0.1, p = 0.043 vs. above 25th percentile).
  
  
  CONCLUSIONS
  Vitamin D deficiency is associated with suppression of resting cardiac autonomic activity, while low 1,25-dihydroxy vitamin D levels are associated with unfavourable cardiac autonomic activity during an acute AngII stressor, offering a potential pathophysiological mechanism that may be acting to elevate CV risk in in populations with low vitamin D status.
authors.affiliation: University of Calgary, 1403 29th St. NW, Calgary, AB T2N 2T9, Canada. mcmann@ucalgary.ca
authors.forename: Michelle C
authors.initials: MC
authors.lastname: Mann
authors.forename: Derek V
authors.initials: DV
authors.lastname: Exner
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Hemmelgarn
authors.forename: Darlene Y
authors.initials: DY
authors.lastname: Sola
authors.forename: Tanvir C
authors.initials: TC
authors.lastname: Turin
authors.forename: Linda
authors.initials: L
authors.lastname: Ellis
authors.forename: Sofia B
authors.initials: SB
authors.lastname: Ahmed
mesh_terms: D000328:Adult; D000804:Angiotensin II / Q000009:adverse effects; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000378:metabolism; D001794:Blood Pressure; D002318:Cardiovascular Diseases / Q000097:blood* / Q000150:complications; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D012307:Risk Factors; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000150:complications
chemical_list: D000804:Angiotensin II; D014807:Vitamin D