Prospective Associations of Vitamin D Status with Beta-cell function, Insulin Sensitivity and Glycemia: The Impact of Parathyroid Hormone Status

  1. Ravi Retnakaran1,2,6
  1. 1Leadership Sinai Centre for Diabetes, Mount Sinai Hospital, Toronto, Canada
  2. 2Division of Endocrinology, University of Toronto, Toronto, Canada
  3. 3Department of Nutritional Sciences, University of Toronto, Toronto, Canada
  4. 4Keenan Research Centre for Biomedical Science of St. Michael’s Hospital, Toronto, Canada
  5. 5Division of Obstetrics and Gynecology, University of Toronto, Toronto, Canada
  6. 6Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada
  1. Corresponding Author: Ravi Retnakaran E-mail: rretnakaran{at}mtsinai.on.ca

Abstract

Previous studies have yielded conflicting findings on the relationship between low vitamin D (25-OH-D) and impaired glucose homeostasis. In this context, we hypothesized that combined assessment of 25-OH-D with its regulator parathyroid hormone (PTH) may be required for optimal evaluation of the impact of vitamin D status on glucose metabolism. Thus, we evaluated the prospective associations of 25-OH-D and PTH at 3-months postpartum with beta-cell function (Insulin Secretion-Sensitivity Index-2 (ISSI-2)), insulin sensitivity (Matsuda index) and glycemia at 12-months postpartum in 494 women undergoing serial metabolic characterization. Notably, 32% of those with pre-diabetes/diabetes at 12-months postpartum had both vitamin D deficiency and PTH in the highest tertile at 3-months postpartum. On multiple-adjusted linear regression analyses, vitamin D deficiency/insufficiency with PTH in the highest tertile at 3-months independently predicted poorer beta-cell function (P=0.03) and insulin sensitivity (P=0.01), and increased fasting (P=0.03) and 2-hour glucose (P=0.002) at 12-months postpartum. In contrast, vitamin D deficiency/insufficiency with lower PTH did not predict these outcomes. In conclusion, only vitamin D deficiency/insufficiency with increased PTH is an independent predictor of beta-cell dysfunction, insulin resistance and glycemia, highlighting the need for consideration of the PTH/25-OH-D axis when studying the impact of vitamin D status on glucose homeostasis.

  • Received March 25, 2014.
  • Accepted May 20, 2014.

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This Article

  1. Diabetes