The nose is an unusually good place to test an anti-inflammatory compound. Researchers can apply a known allergen directly, wash the nasal passages afterward, and count the inflammatory cells and cytokines that showed up. That design has been used twice to test broccoli sprout extract in humans, once against diesel exhaust particles and once against seasonal grass pollen, and the two studies did not produce the same answer.
Key Takeaways
- A study using intranasal diesel exhaust particle challenge found four days of broccoli sprout extract reduced total nasal cell counts by 54 percent compared with the unprotected challenge (p < 0.001) [1].
- That study used broccoli sprout extract delivering 100 micromoles of sulforaphane daily in mango juice for four days before the challenge [1].
- A separate randomized trial in 47 patients with confirmed grass pollen allergic rhinitis tested broccoli sprout extract with and without nasal steroid spray over three weeks [2].
- The pollen trial measured peak nasal inspiratory flow, total nasal symptom scores, and nasal mucus cytokines, a more clinically meaningful set of endpoints than cell counts alone [2].
- Neither study supports replacing antihistamines or prescribed nasal steroids with a supplement.
The Diesel Exhaust Study
This study started by characterizing what a nasal inflammatory response actually looks like. Twenty-nine participants received an intranasal challenge with 300 micrograms of an aqueous diesel exhaust particle suspension, an amount the researchers described as roughly equivalent to a day of particulate exposure on a Los Angeles freeway. Nasal white blood cell counts rose 66 percent over screening levels and 85 percent over control levels 24 hours after the exposure [1].
After a four-week washout, participants took broccoli sprout extract delivering 100 micromoles of sulforaphane in mango juice daily for four days, then repeated the challenge. Total nasal cell counts fell by 54 percent relative to the unprotected challenge, a difference that reached p < 0.001 [1].
The mechanism proposed was the same Nrf2 phase 2 enzyme pathway that runs through the rest of the sulforaphane literature. Supporting work cited alongside this trial found that sulforaphane increased phase 2 enzyme expression and decreased diesel-particle-induced IL-8, GM-CSF, and IL-1 beta in mouse bronchial epithelial cells, and that broccoli sprout homogenate increased phase 2 enzyme expression in human nasal epithelial cells.
The Grass Pollen Trial
Diesel exhaust particles are a pollutant challenge, not an allergy in the everyday sense. The more directly relevant question is whether this helps people who actually have hay fever, which is what the second study set out to test.
Forty-seven patients with grass-induced allergic rhinitis, confirmed by skin testing and an up-dosing nasal challenge, were randomized into four groups: nasal steroid spray plus broccoli sprout extract, nasal steroid spray plus placebo tablet, saline nasal spray plus broccoli sprout extract, and saline nasal spray plus placebo tablet. Peak nasal inspiratory flow, total nasal symptom scores, and nasal mucus cytokine levels were measured before and after a three-week intervention [2].
The four-arm design is the useful part. It allows separating the effect of the supplement alone, the steroid alone, and the two together, rather than just comparing supplement against nothing. Total nasal symptom score and peak nasal inspiratory flow are also endpoints a patient would actually notice, unlike cell counts in a lavage sample.
Reading These Two Studies Together
The honest read is that broccoli sprout extract has a demonstrated effect on a laboratory measure of nasal inflammation following a pollutant challenge, and that the more clinically framed pollen study exists but does not establish it as an allergy treatment. Two small studies, different challenge models, different endpoints, and no large trial in ordinary seasonal allergy sufferers is not a foundation for recommending it as a hay fever remedy.
There is also a dose question. The diesel study used 100 micromoles of sulforaphane per day, which is at the upper end of what commercial supplements deliver. Anyone comparing this to a product on a shelf should check what the label actually provides, using our dosage guide and our bioavailability explainer, since glucoraphanin listed on a label is not the same as delivered sulforaphane.
What to Do With This
If seasonal allergies are disrupting sleep, work, or breathing, the tools with strong evidence are nasal corticosteroids, antihistamines, and allergen avoidance. Sulforaphane is a research-stage question, not an alternative to any of those. The most defensible position is that if someone is already taking sulforaphane for other reasons, there is preliminary human evidence it affects nasal inflammatory responses, and that is where the claim should stop. Our article on asthma and respiratory research covers the related airway literature.
A Note on the Evidence
Both studies described here are small, and the challenge models used (diesel exhaust particles, controlled pollen challenge) are laboratory conditions rather than everyday allergy exposure. This article is informational and is not medical advice. Do not stop or replace prescribed allergy medication based on it.
Frequently Asked Questions
Does sulforaphane help with hay fever?
There is preliminary human evidence that broccoli sprout extract reduces nasal inflammatory responses after a controlled challenge [1], and a randomized trial has tested it in confirmed grass pollen allergic rhinitis [2]. This is not enough evidence to recommend it as a hay fever treatment.
How much sulforaphane did the nasal studies use?
The diesel exhaust particle study used broccoli sprout extract delivering 100 micromoles of sulforaphane per day in mango juice for four days before the challenge [1].
Can sulforaphane replace a nasal steroid spray?
No. The pollen trial specifically tested broccoli sprout extract alongside nasal steroid spray rather than as a replacement, and nasal corticosteroids have a far larger evidence base for allergic rhinitis.
How quickly did the effect appear?
In the diesel exhaust study, participants took the extract for only four days before the repeat challenge, and the reduction in nasal cell counts was measured at that point [1].
Is this the same as the asthma research?
Related but separate. The nasal studies measure upper airway inflammation after a direct challenge, while the asthma literature looks at lower airway function and symptoms. Both run through the same Nrf2 phase 2 enzyme mechanism.
References
- Heber D et al. Sulforaphane-rich broccoli sprout extract attenuates nasal allergic response to diesel exhaust particles. Food and Function (2014). PMID 24287881
- Yusin J et al. The Effect of Broccoli Sprout Extract on Seasonal Grass Pollen-Induced Allergic Rhinitis. Nutrients (2021). PMID 33920642
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.
