Broccoli May Help Protect Against Respiratory Conditions Like Asthma

This research used broccoli sprouts. They say it is "a readily available food source", but I've never seen it. I've only seen bean sprouts. It does sound like regular broccoli and related foods might be helpful : cabbage, cauliflower, brussel sprouts, ...
See the wikipedia entry below for more cruciferous vegetables.

http://www.sciencedaily.com/releases/2009/03/090302133218.htm

ScienceDaily (Mar. 4, 2009) — Here's another reason to eat your broccoli: UCLA researchers report that a naturally occurring compound found in broccoli and other cruciferous vegetables may help protect against respiratory inflammation that causes conditions like asthma, allergic rhinitis and chronic obstructive pulmonary disease.

Published in the March edition of the journal Clinical Immunology, the research shows that sulforaphane, a chemical in broccoli, triggers an increase of antioxidant enzymes in the human airway that offers protection against the onslaught of free radicals that we breathe in every day in polluted air, pollen, diesel exhaust and tobacco smoke. A supercharged form of oxygen, free radicals can cause oxidative tissue damage, which leads to inflammation and respiratory conditions like asthma.

"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," said Dr. Marc Riedl, the study's principal investigator and an assistant professor of clinical immunology and allergy at the David Geffen School of Medicine at UCLA.
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As in most things, balance is best.

http://en.wikipedia.org/wiki/Cruciferous_vegetables

Cruciferous vegetables can potentially be goitrogenic (inducing goiter formation). They contain enzymes that interfere with the formation of thyroid hormone.[2][3] Cooking for 30 minutes significantly reduces the amount of goitrogens and nitriles. At high intake of crucifers, the goitrogens inhibit the incorporation of iodine into thyroid hormone and also the transfer of iodine into milk by the mammary gland.[4]

Cruciferous vegetables have recently been implicated in some pharmacological drug interactions. These vegetables are powerful inducers of the microsomal cytochrome P450 enzyme CYP1A2, which is responsible for the metabolism of many pharmacological agents[5]. By causing induction of the enzyme, it may incidentally increase the rate of phase I transformations (see pharmacokinetics) of pharmocological agents that are normally metabolized by this enzyme, expediting the process of drug metabolism. This, in turn, could produce drug plasma concentration that is less than the desired therapeutic range.