THURSDAY, March 5 (HealthDay News) -- A compound found in broccoli and other cruciferous vegetables may help prevent respiratory inflammation linked to diseases such as asthma, allergic rhinitis and chronic obstructive pulmonary disease, according to a University of California, Los Angeles, study.

The compound sulforaphane stimulates increased production of antioxidant enzymes in the airway that protect against the large amounts of tissue-damaging free radicals humans breathe in every day in polluted air, pollen, diesel exhaust and tobacco smoke. This tissue damage can lead to inflammation.

The study included 65 people who received varying doses of either broccoli or alfalfa sprout preparations for three days. Broccoli sprouts are the richest natural source of sulforaphane, while alfalfa sprouts don't contain the compound.

"We found a two- to threefold increase in antioxidant enzymes in the nasal airway cells of study participants who had eaten a preparation of broccoli sprouts," principal investigator Dr. Marc Riedl, an assistant professor of clinical immunology and allergy at UCLA's David Geffen School of Medicine, said in a university news release. "This strategy may offer protection against inflammatory processes and could lead to potential treatments for a variety of respiratory conditions."

He added that a "major advantage of sulforaphane is that it appears to increase a broad array of antioxidant enzymes, which may help the compound's effectiveness in blocking the harmful effects of air pollution."

"This is one of the first studies showing that broccoli sprouts -- a readily available food source -- offered potent biologic effects in stimulating an antioxidant response in humans," Riedl said.

The study was published in the March issue of Clinical Immunology.

More research is needed to examine the benefits of sulforaphane for specific respiratory conditions, and it's too early to recommend a particular dosage, Riedl said.