Vitamin D status and its seasonal variations and association with parathyroid hormone concentration in healthy women in Riga

Medicina (Kaunas). 2013;49(7):329-34.

Abstract

The aim of the study was to describe the vitamin D status and its seasonal variations in women living in Riga, Latvia, to examine an association between the concentrations of plasma 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH), and to determine the threshold for plasma 25(OH)D above which there is no further suppression of PTH.

Material and methods: The data of 189 healthy Caucasian women were analyzed. The serum levels of 25(OH)D, PTH, and phosphorus were measured twice a year. All the participants were divided into 3 groups according to vitamin D supplementation and the reproductive status.

Results: The overall mean level of 25(OH)D was 32.8 ng/mL with significantly lower levels being in winter when compared with those in summer (28.2 ng/mL vs. 37.5 ng/mL, respectively; P<0.05). PTH was negatively associated with 25(OH)D. A threshold level of plasma 25(OH)D above which no further suppression of PTH occurred was found to be 38 ng/mL. Postmenopausal women not taking vitamin D supplements and without exposure to sunlight had 25(OH)D deficiency in winter and summer (92% and 88%, respectively). The most significant seasonal fluctuations were seen in the women of the reproductive age not taking vitamin D supplements and without exposure to sunlight, of which 47% had 25(OH)D deficiency in summer and 69% in winter.

Conclusions: An optimal concentration of 25(OH)D was found to be 38 ng/mL. According to this definition, 70.4% of all the healthy women were classified as vitamin D deficient in winter and 59.8% in summer. The highest proportion of vitamin D deficient individuals was found in the group representing the postmenopausal women not taking vitamin D supplements.

MeSH terms

  • Adult
  • Aged
  • Female
  • Humans
  • Latvia / epidemiology
  • Middle Aged
  • Parathyroid Hormone / blood*
  • Seasons*
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / epidemiology
  • White People

Substances

  • Parathyroid Hormone
  • Vitamin D
  • 25-hydroxyvitamin D