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- How does vitamin D work?
A study involving 45-year old British found a U-shaped relation between serum 25(OH)D level and IgE: IgE dropped from 40 kU/l for <10 ng/ml to 25 kU/l for 44 ng/ml, then rose rapidly to 50-60 kU/l for values >54 ng/ml1. This finding suggests that allergies (including anaphylaxis) would be less common in summer than in winter if exposure to allergens were constant year round. However, many allergens such as pollen and insect stings are more common in summer.
Immunoglobulin E (IgE) (a class of antibody) plays an important role by degranulation of mast cells or basophils; higher levels of IgE are associated with increased risk of anaphylaxis.
A mast cell (or mastocyte) is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against pathogens. http://en.wikipedia.org/wiki/Mast_cell
To understand how vitamin D works, it is worthwhile to understand the mechanisms of anaphylaxis. Antigen-presenting cells (APCs) are specialized white blood cells that help fight off foreign substances that enter the body. APCs include a variety of cells including macrophages, dendritic cells and B-cells. They are discussed on this website: http://www.wellness.com/reference/allergies/antigen-presenting-cells/. When they overreact to a food or other material such as insect stings, they can give rise to anaphylaxis or, in less severe fashion, mild allergic reactions.
Griffin et al2 suggested that the hormonal metabolite of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)2D], affected the a number of lymphocytes and APCs through effects on target genes. This concept was reexamined in more detail in a paper by Baeke et al. . The action of 1,25(OH)2D on dendritric cells* is to lower the production of proinflammatory cytokines and increase production of interleukin-10 (IL-10), which has broad anti-inflammatory properties, as well as increase recruitment of T-regulatory cells, a “specialized subpopulation of T cells that act to suppress activation of the immune system and thereby maintain immune system homeostasis and tolerance to self-antigens” http://en.wikipedia.org/wiki/Regulatory_T_cell.
In addition, the antigen-presenting and T-cell stimulatory capacities of monocytes/ macrophages are greatly inhibited by 1,25(OH)2D. 1,25(OH)2D also acts on T and B lymphocytes to inhibit of proinflammatory Th1 cytokines such as IL-2, IFN-γ, and TNF-α and upregulate the production o Th2 cytokines that are not proinflammatory.
The fact that season of birth is associated with food allergic reactions suggests that the effect of vitamin D on the immune system occurs in utero or in early childhood when the system is under development.
* Dendritic cells (DCs) are immune cells forming part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system. That is, they function as antigen-presenting cells. They act as messengers between the innate and adaptive immunity. http://en.wikipedia.org/wiki/Dendritic_cell.
Page last edited: 08 May 2011
- Hypponen, E. Berry, D. J. Wjst, M. Power, C. Serum 25-hydroxyvitamin D and IgE – a significant but nonlinear relationship. Allergy. 2009 Apr; 64 (4): 613-620.
- Griffin, M. D. Xing, N. Kumar, R. Vitamin D and its analogs as regulators of immune activation and antigen presentation. Annu Rev Nutr. 2003; 23117-45.