Vitamin D deficiency during pregnancy may raise the risk of allergies and asthma in offspring

Posted on: March 1, 2015   by  Rebecca Oshiro

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Earlier this year the Journal of Steroid Biochemistry and Molecular Biology published a study from India looking at the expression of immune cells and regulatory enzymes of vitamin D in pregnant women:

Vijayendra chary A, Hemalatha R, Seshacharyulu M, Vasudeva murali M, Jayaprakash D, Dinesh kumar B. Reprint of “Vitamin D deficiency in pregnant women impairs regulatory T cell function”. J Steroid Biochem Mol Biol. 2015; http://dx.doi.org/10.1016/j.jsbmb.2015.01.026

Despite abundant tropical sunshine, 84% of pregnant women in India have a 25(OH)D level less than 22.5 ng/mL. This is thought to be due to the cultural practice of confining pregnant women to indoors and the veil worn by Muslim women.

Vitamin D deficiency in pregnant women has been linked to decreased lung function and an increased risk of atopic allergy in their children. Previous research has found a link between lower vitamin D levels and abnormal concentrations of immune cells. The markers of immune function measured in this study included:

  • Regulatory T cells (Treg cells), which suppress IgE-mediated reactions (which include allergies), and therefore decrease allergic responses. They also are critical in increasing the mother’s tolerance of the fetus. Low Treg cell concentrations have been linked to miscarriage and infertility.
  • B lymphocytes, which contain CD23 and C21 receptors for IgE antibodies and are critical in the normal development and maturation of the immune system.

A total of 153 women from rural and urban areas were included in the study. While visiting the hospital for prenatal checkups, the 25(OH)D levels of the women were measured and they were classified as either vitamin D sufficient, insufficient, or deficient. Vitamin D sufficiency was defined as a 25(OH)D level ≥30 ng/mL, insufficiency was defined as a level between 20 and 29 ng/mL, and deficiency was defined as ≤19 ng/mL.

Concentrations of Treg cells and CD23 and CD21 on the B cells were also measured. After delivery, the cord blood of their infants was analyzed for the concentration of 25(OH)D and these immune cells and receptors.

A representative sample of 8 women was selected from each group of the women (sufficient, insufficient, and deficient) to analyze the expression of mRNA expression of several vitamin D-related receptors and vitamin D regulatory enzymes in the placenta. Measurements included:

  • The vitamin D receptor (VDR)
  • The retinoic acid receptor (RXR), which together with the VDR “reads” the DNA inside a cell, influencing gene expression
  • Vitamin D binding protein (VDBP), which is bound to the majority of 25(OH)D in the blood stream
  • CYP2R1, which hydroxylates both D2 and D3 into 25(OH)D
  • CYP27B1, which converts vitamin D into its active, hormonal form
  • CYP24A1, which degrades vitamin D so it can be excreted

Here are the results of the study:

  • Maternal 25(OH)D levels directly correlated with cord blood 25(OH)D levels (p = .001)
  • The Treg cell population was significantly lower in vitamin D deficient women as compared to sufficient and insufficient women (p < .05).
  • Treg cells concentrations were lower in the cord blood of infants born to vitamin D deficient women when compared to sufficient and insufficient women (p < .05)
  • The proportion of B cells with CD23 expression was significantly higher in vitamin D deficient women as compared to sufficient and insufficient women (p <.05)
  • CD23 expression was higher in the cord blood of infants born to vitamin D deficient women as compared to infants born to sufficient and insufficient mothers
  • VDR expression was down-regulated in the placental tissue of vitamin D deficient women (p < .05)
  • RXR expression was down-regulated in vitamin D deficient and insufficient women (p < .05)
  • CYP27B1 was down-regulated while CYP2R1 was up-regulated in the vitamin D insufficient and deficient women (p < .05)
  • CYP24A1 and VDBP were up-regulated in the placenta of vitamin D insufficient and deficient women (p < .05)

The lower Treg cell concentrations coupled with an increased expression of the CD21 and CD23 expression on B cells may indicate an increased susceptibility to allergic and autoimmune disorders.

The authors interpreted the increased expression of CYP2R1 and CYP24A1 with decreased CYP27B1 as the body’s attempt to increase the concentration of active vitamin D in a vitamin D deficient state. Previous research has linked lower VDBP levels to increased protection against the symptoms of vitamin D deficiency.

The authors concluded,

“Impaired maternal vitamin D during pregnancy may influence a spectrum of immune cells in the mother and placenta, which in turn may be linked to allergy and asthma in neonates. The role of vitamin D in immune function and inflammation in pregnant women must not be underestimated…..and supplementation in pregnant women must be considered.”

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