Development of a standardized methodology for double-blind, placebo-controlled food challenge in patients with brittle asthma and perceived food intolerance

OBJECTIVE

To develop a standardized, double-blind, placebo-controlled, food challenge (DBPCFC) methodology for identifying food intolerance in patients with brittle asthma.

SUBJECTS/SETTING

Patients with brittle asthma and perceived food intolerance were studied in hospital.

DESIGN

Each of 3 protocols began with 5 days of dietary exclusion. Protocol 1 consisted of open food challenges in 29 patients, protocol 2 consisted of 2 daily DBPCFCs in 22 patients, and protocol 3 involved 1 daily DBPCFC in 18 patients. Total immunoglobulin E level was measured and food-specific radioallergosorbent tests and skin prick tests were conducted. A standard panel of hyperallergenic foods were masked in a soup (developed specially for this study) for every food challenge. Peak expiratory flow, forced expiratory volume, and symptoms were assessed as objective measures of response. Open food challenges at home followed each protocol. Each protocol took approximately 14 days in the hospital and 4 to 6 months at home.

RESULTS

For protocols 1, 2 and 3, positive reactions were experienced by 52%, 55%, and 66% of patients, respectively. Radioallergosorbent tests and skin prick tests were shown to have 40% and 71% sensitivity, respectively, and 74% and 77% specificity for predicting a positive food challenge.

APPLICATIONS/CONCLUSIONS

The high prevalence of food intolerance in patients with brittle asthma was confirmed, as was the poor positive predictive value of skin prick tests and radioallergosorbent tests. The food challenge method developed enables standardized identification of food intolerances in patients with brittle asthma and may be useful in other groups.

Dietary antioxidants and magnesium in type 1 brittle asthma: a case control study

BACKGROUND

Type 1 brittle asthma is a rare form of asthma. Atopy, psychosocial factors and diet may contribute to this condition. As increased dietary magnesium has a beneficial effect on lung function and selenium, vitamins A, C and E have antioxidant properties, a study was undertaken to test the hypothesis that patients with brittle asthma have diets deficient in these nutrients compared with subjects with non-brittle asthma and healthy adults.

METHODS

A case control study of the dietary intakes of 20 subjects with brittle asthma, 20 with non-brittle asthma, and 20 healthy adults was performed using five day weighed dietary records. Intake of magnesium was the primary outcome measure with selenium and vitamins A, C and E as secondary outcomes. Serum levels were measured at the same time as the dietary assessment.

RESULTS

Sixty subjects (27 men) of mean age 49.5 years were recruited and completed the study. Subjects with brittle asthma had statistically lower median dietary intakes of vitamins A and E than the other groups (vitamin A: brittle asthma 522.5 micrograms/day, non-brittle asthma 869.5 micrograms/day, healthy adults 806.5 micrograms/day; vitamin E: brittle asthma 4.3 mg/day, non-brittle asthma 4.6 mg/day, healthy adults 4.5 mg/day). Median dietary intakes for the other nutrients were not significantly different between groups. Serum levels were within normal ranges for each nutrient in all subjects. Intakes less than the reference nutrient intake (RNI) for magnesium and vitamins A and C, and less than the safe intake (SI) for vitamin E were more likely in patients with brittle asthma than in those with non-brittle asthma.

CONCLUSION

Nutrient deficiency and reduced antioxidant activity may contribute to disease activity in type 1 brittle asthma, although a prospective study of replacement therapy will be needed to confirm this hypothesis.