ACAAI 2011: Diet's Role in Immune Therapy Difficult to Study

BOSTON--Thomas B. Casale, MD, FACAAI, professor of medicine at Creghton University School of Medicine in Omaha, Neb., gave the Ira Finegold Lecture today at the American College of Allergy, Asthma, & Immunology’s annual meeting.

Casale spoke about the role that diet and supplement can have on immune therapy. Immune tolerance is a starting point. “For allergies, the immune system could be trained to ignore allergens like pollen and cat dander but still fight bacterial pathogens,” he said.

The goals are to decrease pathologic immune responses, rather than necessarily to return to an immunologically naïve or unresponsive state; stop treatment with persistent pathologic and clinical improvements; and have a favorable risk/benefit ratio.

Casale discussed whether dietary supplements can impact asthma and allergies. Herbal supplements are gaining in popularity but there are concerns about their efficacy and safety, he said. In China, where herbal therapies are considered conventional, studies looked at consumption of omega 3 plus fish oil. High levels are associated with regular fish consumption under the age of 12 months, which can reduce allergen sensitivity for at least the first four years of life.

Omega 3 fatty acid supplement alone doesn’t appear to improve asthma or allergic rhinitis symptoms. Casale said studies showing whether use of omega 3 would prevent allergies and asthma must control for who took the supplement and when. Was it the mother and did she take it during pregnancy or during breastfeeding? Another important factor is the duration of treatment. These variables make it “very difficult to design good studies.”

Vitamin D is potentially important to allergies and asthma, Casale said. “The prevalence of asthma has been increasing in parallel with trends in vitamin D deficiency. Vitamin D deficiency has been associated with epidemiologic patterns observed in the asthma epidemic.” A study of more than 6,000 children aged 1 to 21 estimated that 9 percent, 7.6 million, American children, are vitamin D deficient, and another 61 percent are vitamin D insufficient. Exposure to sunlight isn’t the answer: 28 percent of those studied in Costa Rica were deficient and 51 percent of Hawaiians, despite a rate of sun exposure of 29 hours per week, were deficient.

Casale said studies have found no association between vitamin D and the presence or absence of asthma. Studies suffer, however, from a lack of long-term follow-up and are uncorrected for seasonal variances, he said. Plus, often only a single measurement of serum 25(OH)D3 is taken. “Long-term, double blind, randomized, controlled trials are lacking.”

“We know that vitamin D is the strongest predictor of asthma with an odds ratio of 4.82,” Casale said. Vitamin D plays role in fetal lung growth and maturation and higher prenatal intake has a potential role against wheezing illnesses. However, kids born to mothers with higher levels of vitamin D have increased prevalence of asthma.

“There are a lot of unanswered questions,” Casale said. “The studies are confusing and divergent. The available literature regarding dietary manipulation as asthma/allergy therapy is largely unconvincing. There are few interventional studies with positive, clinically relevant endpoints.”