Vitamin D, the immune system and asthma

In reading other eczema blogs, I stumbled upon a paper from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2812815 which I will try to accurately summarize:

Vitamin D, the immune system and asthma

which is dated November 2009 and written by Nancy E Lange, MD, MPH, Augusto Litonjua, MD, MPH, Catherine M Hawrylowicz, PhD, and Scott Weiss, MD from Brigham & Women's Hospital. I'm not familiar with the authors or any of their previous work, but I did find this interesting.  Here are a few excerpts:

This article will summarize some of the emerging evidence on the complex role of vitamin D in the immune system relevant to asthma, and provide an overview of investigations thus far linking vitamin D and asthma.

Key issues

• Recent evidence points to vitamin D as an essential immune system regulator.
• Vitamin D deficiency and insufficiency are widespread, regardless of latitude.
• Low vitamin D levels have been linked with many immune-mediated diseases and cancers.
• Basic science and animal models demonstrate the multiplicative effects of vitamin D on cells of the immune system and cytokine profiles.
• Genetic and epidemiologic studies have shown an association between asthma and vitamin D.
• The rising prevalence of asthma may be linked to vitamin D deficiency.
• Further investigation is needed to fully understand the role of vitamin D in the development of allergy and asthma.

Extraskeletal effects of vitamin D

In humans, vitamin D is obtained through ultraviolet B exposure, diet and supplement intake. It is converted to 25-hydroxyvitamin D₃ by the liver. Circulating 25-hydroxyvitamin D₃ is converted to the active form, 1,25-dihydroxyvitamin D₃, in a variety of sites including the kidney and cells of the immune system. Experimental evidence suggests an effect of 1,25-dihydroxyvitamin D₃ on multiple different processes and cell types. In the immune system it leads to a decrease in the Th1 response, thought to be the mechanism involved in the association between low vitamin D levels and a variety of autoimmune diseases. It modulates the Th2 response affecting cytokines such as IL-4, IL-5 and IL-13. This is one possible link between vitamin D and allergy/asthma. It has been shown to upregulate T-regulatory cells, leading to an increase in the synthesis of the anti-inflammatory cytokine IL-10. In macrophages, vitamin D upregulates synthesis of the antimicrobial peptide cathelicidin, which may enhance the ability to fight infections. In airway smooth muscle cells, it has been shown to modulate chemokine release. Vitamin D may play a role in fetal lung development and in the differentiation of type II pneumocytes and surfactant secretion. Vitamin D has also been associated with a lower incidence of and mortality from a variety of cancers.

The paper concludes with "The role of vitamin D in the pathogenesis of immune-mediated diseases such as asthma is only beginning to be understood. Several ongoing or planned human clinical trials are aimed at clarifying this link in the next 5 years. . . The elucidation of the precise roles of vitamin D in the immune system and in the pathogenesis of multiple diseases has the potential to have profound effects on our ability to prevent and treat these disorders."

I hope my summary was an accurate account, and no disservice was done.