Sulforaphane

What sulforaphane is

Sulforaphane is an isothiocyanate, that is, a mustard oil. In the plant it is present as the inactive precursor glucoraphanin. Only when cells are damaged, for example during chewing, does glucoraphanin meet the plant’s own enzyme myrosinase and become sulforaphane. Young broccoli sprouts contain particularly large amounts of glucoraphanin.

Cooking destroys myrosinase. Gut bacteria then take over part of the conversion, but less reliably. How much difference this makes is shown by a small study with 12 adults: after 200 g of cooked broccoli with 1 g of mustard powder, 44.7 µmol of a sulforaphane breakdown product per gram of creatinine were found in the urine, without mustard powder only 9.8. Mustard seed itself contains myrosinase and steps in for the destroyed enzyme.

How it is supposed to work

Sulforaphane activates the transcription factor Nrf2. This switches on a program of protective genes, including phase II detoxification enzymes that couple pollutants to glutathione and make them excretable. Unlike with many plant compounds, this step can be measured directly in humans.

That is exactly what the studies in Qidong did, a region with high air pollution. They measured how much glutathione-conjugated benzene and acrolein ends up in the urine. A follow-up study with 170 participants also showed a dose-response relationship: only the full dose significantly increased benzene excretion, by 63.2 %, the half and one-fifth doses did not. From this, the authors derive an effective amount of about 25 µmol of excreted sulforaphane metabolites per day. Important in practice: bioavailability did not decrease over 12 weeks of daily intake, so no habituation was seen. For blood glucose there is a separate mechanism: in liver cells, sulforaphane lowered glucose production via Nrf2. For autism, anti-inflammatory and mitochondrial effects are also discussed.

User reports

After the first autism study, the researchers followed up with the families until 2016. 16 of 26 families in the sulforaphane group responded; 9 of the young men were still taking a sulforaphane supplement, and one more person was planning to. The reports of the caregivers were published, many of whom describe positive changes. This is an uncontrolled case series and not proof of efficacy, but it shows how those affected experienced the effect themselves.

What matters in a product

The Institute of Pharmaceutical Biology at the University of Münster analyzed 14 broccoli food supplements and found very large differences in quality. In several products, glucoraphanin was not detectable at all. Then there is the question of conversion: if a supplement also supplies active myrosinase, sulforaphane was 3 to 4 times more bioavailable in one study. In a more recent crossover study with 16 people, mustard seeds raised bioavailability from 18.6 to 39.8 %.

What the studies show

Air pollutants in Qidong

Randomized, placebo-controlled, 291 participants, 12 weeks. The sprout beverage supplied 600 µmol of glucoraphanin and 40 µmol of sulforaphane daily. Excretion of the benzene conjugates rose by 61 %, that of the acrolein conjugates by 23 %; crotonaldehyde remained unchanged. This is a pharmacological endpoint; whether it prevents diseases was not studied.

The first autism study

Double-blind, 29 young men aged 13 to 27 on sulforaphane and 15 on placebo, 50 to 150 µmol daily depending on body weight over 18 weeks. Scores on the Aberrant Behavior Checklist fell by 34 %, those on the Social Responsiveness Scale by 17 %; with placebo they changed by less than 3.3 %. After discontinuation, the scores rose back toward baseline.

Prediabetes and gut flora

Double-blind, 35 people with broccoli sprout extract and 39 with placebo over 12 weeks. The predefined target of 0.3 mmol/l lower fasting blood glucose was missed; overall the value fell by 0.2 mmol/l. A subgroup with a particular metabolic profile responded more strongly, with 0.4 mmol/l, and these people more often had gut bacteria with a gene needed for the conversion of glucoraphanin.

Where the data stop

For cancer prevention there are no clinical endpoints in humans. A systematic review of 8 randomized trials in cancer patients found altered biomarkers and inconsistent PSA values; a meta-analysis was not possible because of the differences between the trials. The protective effects come from laboratory and animal experiments; a systematic review of 9 animal studies found, for example, fewer skin tumors after carcinogen and UVB exposure.

In autism, the effect does not hold in the meta-analysis: after 18, 22 and 36 weeks the difference was no longer significant, and heterogeneity was high. In schizophrenia, sulforaphane did not improve overall symptoms in 4 studies with 369 patients. Negative symptoms improved slightly after 12 weeks, by 1.06 points, but the effect did not last; at least fewer patients discontinued treatment with sulforaphane. For blood glucose, the prediabetes study missed its primary target, even though an older study in poorly controlled type 2 diabetes and overweight found lower fasting values and HbA1c. Statements about the liver as a detoxification organ are based on excretion markers, not on liver values.

Status, approval and legal

Broccoli sprouts, powders and extracts are foods or food supplements in Germany. Health claims on broccoli and sulforaphane, for example on cell protection or gastrointestinal health, have not been authorized by the EU after review by EFSA. There is no legal maximum amount, and the contents of supplements vary widely. Doping relevance is not described in the literature reviewed.

Safety

In the autism studies, irritability, insomnia, constipation and headaches occurred, but not more often than with placebo: irritability, for example, in 10.0 % of the 180 participants on sulforaphane and in 8.5 % of the 153 in the control groups. In the prediabetes study there were gastrointestinal complaints; there were no serious side effects. In the first, high-dose autism study, 2 participants each had one seizure; anyone with epilepsy should discuss this with a doctor. The frequently cited concern about the thyroid was not confirmed in a study with 45 women over 84 days; TSH, thyroid hormone and autoimmune status remained the same. There is no official upper limit.

Sources

• Egner et al., Cancer Prev Res 2014
• Chen et al., Am J Clin Nutr 2019
• Long et al., BMC Pharmacol Toxicol 2025
• Wang, Ren, Li, EXCLI J 2025
• Singh et al., PNAS 2014
• Dwibedi et al., Nat Microbiol 2025
• ElKhalifa et al., Front Oncol 2023
• Chartoumpekis et al., Food Chem Toxicol 2019
• Okunade et al., Mol Nutr Food Res 2018
• University of Münster, broccoli food supplements