Before I begin this post, allow me to restate that I am not a doctor, and therefore my understanding of information presented at the AAAAI 2008 meeting is not 100% clear. That said, I will do my best to accurately relay what I learned about the role of vitamin D in atopic disease.
Dr. Matthias Wjst, MD, explained that dietary sources of vitamin D are not ideal. It is best to get vitamin D from natural sunlight exposure. In fact, dietary supplementation of vitamin D may be related to the increase in allergies and asthma.
Early vitamin D3 supplementation has been linked to asthma. Dr. Wjst also pointed out that inhabitants of the islands of Tristan da Cunha have a very high incidence of allergies and asthma – and they also consume a very high amount of dietary vitamin D from sea bass.
Many ‘allergy’ genes seem to be regulated by vitamin D, and vitamin D also appears to regulate an antimicrobial response within the immune system. Dr. Wjst proposed that oral vitamin D supplementation could be a not-so-visible component of the hygiene hypothesis.
The hygiene hypothesis is a hot topic among allergists; it suggests that the prevalence of allergic diseases in modern, developed societies is related to our overly hygienic lives. For example, kids who grow up on farms usually have lower rates of allergies and asthma. However, if a child stays indoors in a sterile environment all the time, then his immune system is never challenged and never has a chance to ‘learn’ what it should attack. Thus, the immune system overreacts to substances like pollen.
Dr. Wjst suggested that perhaps oral vitamin D supplementation early in life leads to fewer infections and therefore more allergies; this is another way of looking at the hygiene hypothesis.
Dr. Margherita Cantorna, PhD, presented molecular evidence for the role of vitamin D in asthma and autoimmune diseases. A great deal of this evidence went over my head, but I did learn that T-cells have vitamin D receptors, and that vitamin D deficiency exacerbates autoimmune diseases like multiple sclerosis, lupus, arthritis, type I diabetes, and inflammatory bowel disease. Also, inflammatory bowel disease is much more prevalent in urban areas, Northern areas, and developed countries.
So… It looks like too much vitamin D in the diet can increase the incidence of allergic diseases; however, too little vitamin D can make allergic diseases worse.
Dr. Cantorna told attendees that vitamin D seems to normalize T-cell function in the immune system.
Here's the key point: People generally don't get hyper-doses of vitamin D by spending time in the sun; however, it's easy to get hyper-doses of vitamin D through oral supplementation.
My takeaway: I'm going to try to spend more time outdoors in the sun, allowing the vitamin D machinery in my skin to do its job.
This was not the first time I had heard about the possible role of vitamin D in atopic disease. Several months ago I interviewed Dr. Thomas A.E. Platts-Mills, former President of the AAAAI and one of the world's preeminent allergy researchers, and he alluded to the possible vitamin D connection.
Dr. Platts-Mills believes that the hygiene hypothesis does not offer a full explanation. He thinks that the rise in allergies and asthma is due to the fact that we have essentially become an indoor species:
‘Yes, you need cleanliness in order to get allergy, but the rise in asthma from 1960 onward, which was occurring among allergic patients, is much more likely to be due to the major change in lifestyle that occurred then, which is that we moved indoors and have essentially become an indoor species. In the 1950s, children would spend three hours a day outdoors playing. From about 1960 onwards, that's progressively decreased so that now it's unusual for children to go outdoors. The outdoor exposure could be beneficial because it allows the children to open up their lungs and exercise their lungs; it could be beneficial because they don't get so fat; it could be beneficial because their environment is better; or even, as has recently been suggested, because they get more exposure to the sun and therefore aren't vitamin D deficient.’
To read the full interview with Dr. Platts-Mills, see Dr. Thomas A.E. Platts-Mills on Allergen Avoidance through Environmental Control.
For more information about the role of vitamin D in atopic disease, also see Geographic Differences in EpiPen Prescriptions – Sunlight, Vitamin D & Allergies.