GradedHealth

Do broccoli sprouts have health benefits? What the small trials show

Small trials suggest broccoli sprouts may help blood sugar and hay fever. The evidence is early, and several trials found no benefit.

Published October 2026

Short answer

Small, early trials suggest broccoli sprouts may modestly lower blood sugar and ease some hay fever symptoms. Other trials found no benefit, so the evidence is limited. Evidence grade C (Limited). Small trials (most under 100 people) with mainly blood-marker outcomes; downgraded for small size and surrogate outcomes, with mixed results.

Key takeaways

  • Two small trials in people with prediabetes or type 2 diabetes found modest drops in blood sugar or insulin resistance [1][2].
  • Two trials of high-glucoraphanin broccoli found LDL 'bad' cholesterol fell about 5 to 7%, against about 2% on ordinary broccoli [3].
  • Autism results conflict: one trial in young men improved behaviour scores, while a trial in children found no significant change [4][5].
  • In people with hay fever, sprout extract added to a nasal steroid spray improved nasal airflow more than the spray with placebo [6].

The short version

The broccoli sprouts are the richest food source of sulforaphane, a plant compound that switches on the body's own antioxidant defences [7]. Small trials suggest sprouts may help blood sugar a little and ease some hay fever symptoms [1][2][6]. The evidence is early: most trials had fewer than 100 people, and several found no benefit [7][8].

What the studies show

In a 12-week trial of 74 people with prediabetes, a daily broccoli sprout extract did not reach its main goal, but fasting blood sugar fell about 0.2 mmol/L more than with placebo [1]. A 4-week trial in 63 people with type 2 diabetes found that 10 grams of broccoli sprout powder a day lowered insulin levels and a measure of insulin resistance, at borderline statistical strength [2].

Two trials with 130 people tested high-glucoraphanin broccoli, which is not sprouts, eaten at 400 grams a week for 12 weeks. LDL cholesterol fell 5 to 7% on that broccoli, against about 2% on ordinary broccoli [3].

Autism is the most mixed result. In a placebo-controlled trial of 44 young men with autism, 18 weeks of sulforaphane lowered a behaviour checklist score by 34% and a social responsiveness score by 17%, while placebo changed little [4]. A trial of 40 children aged 3 to 7 found no significant change on behaviour or autism scales [5].

In a trial of 70 children with ADHD, adding sulforaphane to methylphenidate for eight weeks led to larger drops in ADHD rating scores than methylphenidate with placebo, with large effect sizes [9].

In 52 men with fatty liver, two months of broccoli sprout capsules lowered two liver enzymes slightly (ALT from a median of 54 to 48.5 international units per litre); placebo did not [10].

In 47 people with grass-pollen hay fever, adding sprout extract to a daily nasal steroid spray improved nasal airflow more than the spray with placebo; symptom scores improved only at some time points [6].

After heavy weight training, 10 young men who took 30 mg of sulforaphane a day for four weeks had lower blood levels of creatine kinase, a muscle-damage marker, than when they took placebo [11]. A later crossover trial in 15 people found that 320 micrograms of broccoli-derived glucoraphanin for two weeks did not speed recovery in soreness, strength or muscle markers after hard exercise [12].

In 37 former smokers who finished a 12-month trial, sulforaphane lowered Ki-67, a marker of cell growth in the airways, by 20%, while placebo rose 65%. Biopsy scores did not change significantly [13]. This is a tissue marker, not a count of lung cancers [13].

Not every result was positive. In 40 adults with asthma, eating 100 grams of broccoli sprouts a day for three days raised blood sulforaphane but did not lower airway inflammation or improve lung function [7].

A 2024 meta-analysis of observational studies linked more broccoli eating with lower cancer risk. Cohort studies covering about 700,000 people showed an 11% lower risk [14]. This covers broccoli in general, not sprouts, and observational studies cannot prove cause [14].

The nuances

Doses differed widely between trials, from 30 milligrams of sulforaphane a day to 100 grams of sprouts, so there is no agreed dose [9][7].

Several trials have industry ties. The blood sugar trial's authors hold a patent licensed to a company, and the autism trial's patents are licensed to Brassica Protection Products [1][4].

Results are also uneven. A 2024 trial in 25 people on hemodialysis found no change in two inflammation-related genes [8]. A 2025 review noted that about half of completed sulforaphane trials remain unpublished [15].

On safety, the blood sugar trial reported mostly stomach upset and no severe adverse events [1]. A 12-week trial of a sprout-derived beverage in 45 women found no change in thyroid function [16]. In a 24-person study, sulforaphane alone did not change the liver enzyme that clears many medicines across the group, but in people with the highest starting activity it lowered it, so medicine interactions are possible [17]. The trials read did not report pregnancy, breastfeeding or upper-limit data, so talk to a doctor before taking sprout extracts if you are pregnant, breastfeeding, have kidney disease [8] or take medicines.

What this means for you

Sprout extracts were well tolerated in the blood sugar trial, with stomach upset the main side effect [1]. The most promising results so far are for blood sugar and hay fever, and both come from small trials [1][6]. Eating broccoli regularly is linked to lower cancer risk in observational studies, but that does not show that sprouts or extracts would have the same effect [14]. If you are considering sprout extracts for blood sugar or allergies, talk to a doctor first, especially if you take diabetes or allergy medicines [1][17].

Go deeper

References

  1. Effect of broccoli sprout extract and baseline gut microbiota on fasting blood glucose in prediabetes: a randomized, placebo-controlled trial.. Nat Microbiol, 2025.
  2. Effect of broccoli sprouts on insulin resistance in type 2 diabetic patients: a randomized double-blind clinical trial.. Int J Food Sci Nutr, 2012.
  3. Diet rich in high glucoraphanin broccoli reduces plasma LDL cholesterol: Evidence from randomised controlled trials.. Mol Nutr Food Res, 2015.
  4. Sulforaphane treatment of autism spectrum disorder (ASD).. Proc Natl Acad Sci U S A, 2014.
  5. Sulforaphane Treatment in Children with Autism: A Prospective Randomized Double-Blind Study.. Nutrients, 2023.
  6. The Effect of Broccoli Sprout Extract on Seasonal Grass Pollen-Induced Allergic Rhinitis.. Nutrients, 2021.
  7. A Randomized Controlled Trial of the Effect of Broccoli Sprouts on Antioxidant Gene Expression and Airway Inflammation in Asthmatics.. J Allergy Clin Immunol Pract, 2016.
  8. Sulforaphane Supplementation Did Not Modulate NRF2 and NF-kB mRNA Expressions in Hemodialysis Patients.. J Ren Nutr, 2024.
  9. Sulforaphane Adjunct to Methylphenidate for Attention-deficit/Hyperactivity Disorder: A Randomized, Double-blind, Placebo-controlled Trial.. Clin Neuropharmacol, 2025.
  10. Sulforaphane-rich broccoli sprout extract improves hepatic abnormalities in male subjects.. World J Gastroenterol, 2015.
  11. Oral chronic sulforaphane effects on heavy resistance exercise: Implications for inflammatory and muscle damage parameters in young practitioners.. Nutrition, 2021.
  12. Short-Term Effects of Broccoli-Derived Glucoraphanin on Recovery from Eccentric Muscle Damage: A Double-Blind Randomized Crossover Study.. Nutrients, 2026.
  13. Randomized Phase II Clinical Trial of Sulforaphane in Former Smokers at High Risk for Lung Cancer.. Cancer Prev Res (Phila), 2025.
  14. Broccoli Consumption and Risk of Cancer: An Updated Systematic Review and Meta-Analysis of Observational Studies.. Nutrients, 2024.
  15. Sulforaphane as a potential therapeutic agent: a comprehensive analysis of clinical trials and mechanistic insights.. J Nutr Sci, 2025.
  16. Broccoli sprout beverage is safe for thyroid hormonal and autoimmune status: Results of a 12-week randomized trial.. Food Chem Toxicol, 2019.
  17. Sulforaphane is not an effective antagonist of the human pregnane X-receptor in vivo.. Toxicol Appl Pharmacol, 2013.