Consumption of broccoli sprouts led to a two- to three-fold increase in levels of antioxidant enzymes linked to the protection of human airways against oxidative tissue damage, which leads to inflammation and respiratory conditions like asthma, according to findings published in Clinical Immunology.
"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 lead researcher Marc Riedl from the David Geffen School of Medicine at UCLA.
The tissue of cruciferous vegetables, like broccoli, cauliflower, cabbage and Brussels sprouts, contain high levels of the active plant chemicals glucosinolates. These are metabolised by the body into isothiocyanates, which are known to be powerful anti-carcinogens. The main isothiocyanate from broccoli is sulphoraphane.
"We found a two- to three-fold increase in antioxidant enzymes in the nasal airway cells of study participants who had eaten a preparation of broccoli sprouts," said Riedl. "This strategy may offer protection against inflammatory processes and could lead to potential treatments for a variety of respiratory conditions."
The study extends out understanding of the potential health benefits of broccoli, with previous studies reporting that the isothiocyanates exert powerful anti-carcinogenic activity.
Listen to your mother! Eat your broccoli!
Riedl and his co-workers recruited 65 people and assigned them to receive varying oral doses of sulforaphane-containing broccoli sprouts or non-sulforaphane-containing alfalfa sprouts for three days. Rinses of nasal passages were collected at before and after the study and used to quantify gene expression of antioxidant enzymes, including glutathione-s-transferase M1 (GSTM1), glutathione-s-transferase P1 (GSTP1), NADPH quinone oxidoreductase (NQO1), and hemoxygenase-1 (HO-1), in cells of the upper airways.
No adverse effects were reported by the subjects, while the nasal rinses showed significant and dose-dependent induction of the antioxidant enzymes at broccoli sprout doses of 100 grams and higher, compared with the alfalfa placebo group.
Indeed, at a broccoli sprout dose of 200 grams (the maximum tested) a 101-per cent increase of GSTP1 and a 199-per cent increase of NQO1 were reported.
"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," said Riedl.
The results of the study provide “vital information for planning additional clinical trials”, said the researchers. In particular, they noted that future human studies are necessary to “thoroughly investigate the potential beneficial effects of Phase II enzyme induction on environmentally-induced oxidative stress and associated allergic airway inflammation”.
According to the European Federation of Allergy and Airway Diseases Patients Association (EFA), over 30m Europeans suffer from asthma, costing Europe €17.7bn every year. The cost due to lost productivity is estimated to be around €9.8bn.
Source: Clinical Immunology March 2009, Volume 130, Issue 3, Pages 244-251“Oral sulforaphane increases Phase II antioxidant enzymes in the human upper airway” Authors: M.A. Riedl, A. Saxon, D. Diaz-Sanchez