Sulforaphane Supplements: Why Myrosinase Decides What You Absorb
If you have already decided to buy a sulforaphane supplement, the number that decides whether it works is not the one printed largest on the front of the bottle. Most products in this category do not contain sulforaphane at all. They contain a precursor called glucoraphanin, and whether that precursor ever becomes the compound you are paying for depends on an enzyme that heat and processing can destroy. This guide covers what human trials actually measured, what they dosed, and how to read a label so you know what you are buying.
Why the Bottle May Not Contain What You Think
Here is the fact most product pages leave out. Broccoli does not contain sulforaphane. It contains glucoraphanin, a stable precursor that sits in the plant until something breaks it apart.
Sulforaphane appears only when glucoraphanin meets myrosinase, an enzyme stored in a separate compartment of the plant cell. Chop, chew, or blend the vegetable, and the two mix.
That separation matters commercially. Extraction, drying, and heat treatment can strip out the enzyme while leaving the glucoraphanin intact. A label can show an impressive precursor count next to a product whose conversion machinery is gone.
What is left is a supplement that asks your gut bacteria to finish the job. Across the clinical literature, formulation is one of the strongest predictors of how much compound actually reaches the bloodstream [1].
That is why two bottles can carry similar glucoraphanin numbers and land in completely different places. One has already solved the conversion problem. The other has outsourced it to bacteria that may or may not cooperate.
Glucoraphanin to Sulforaphane and the Myrosinase Step
What Myrosinase Does
Myrosinase is the enzyme that converts glucoraphanin into sulforaphane. In a fresh sprout it works the moment the plant tissue is damaged. In a capsule it works only if the manufacturer kept it alive through processing, or deliberately added it back.
When the enzyme is present and active, the difference is not subtle. Human work found that sulforaphane from preparations delivered with active plant myrosinase was 3 to 4 times more bioavailable than the same glucoraphanin delivered without it [2].
Why Gut Bacteria Are an Unreliable Backup
Your gut bacteria do carry enzymes that can convert glucoraphanin. The problem is consistency. Bacterial conversion varies widely between people, and it depends on which strains happen to be living in your gut that week.
That variability shows up in the data. In a crossover trial comparing a sulforaphane-rich beverage with a glucoraphanin-rich one, the spread between individual participants was considerably wider on the glucoraphanin side, and elimination was slower [3].
Myrosinase, not the glucoraphanin number, decides how much sulforaphane your body actually gets.
That is why the enzyme source, not the total broccoli content, is the single most useful thing to look for on a label.
The Human Number That Changes How You Shop
The cleanest demonstration comes from a 50-person crossover trial that compared two broccoli sprout beverages. One was rich in sulforaphane and had already been converted. The other was rich in glucoraphanin and delivered without active enzyme.
Researchers measured how much sulforaphane and its metabolites came out in participants' urine. The sulforaphane-rich beverage recovered a mean of 70 percent of the dose. The glucoraphanin-rich beverage recovered a mean of 5 percent [3].
Same plant family, same starting molecule, and a gap wide enough to see in a urine test. The only difference was whether the conversion had already happened before anyone drank it.
That is why two products can both say broccoli sprout extract on the front of the bottle and behave nothing alike.
Practically, that 5 percent figure is roughly what a glucoraphanin-only product delivered in that trial. The precursor is real and the dose may be honestly stated, but most of it never finishes the journey to the compound the label implies.
Why Myrosinase Beats a Big Glucoraphanin Number
Once the enzyme matters, the marketing numbers change meaning. A larger glucoraphanin figure does not help if nothing converts it.
Adding Mustard Powder to Cooked Broccoli
Cooked broccoli has lost its enzyme, which makes it a useful test case. In a randomized crossover study, 12 healthy adults ate 200 grams of cooked broccoli, with and without 1 gram of powdered brown mustard, a concentrated myrosinase source.
Mean urinary SF-NAC rose from 9.8 to 44.7 micromoles per gram of creatinine, over four times higher [4]. Nothing about the broccoli changed. The mustard put the missing enzyme back.
The Newest Human Trial
A 2026 randomized, double-blind crossover study in 16 people tested a glucoraphanin-rich broccoli seed extract against the same extract combined with mustard-seed myrosinase.
Bioavailability doubled, from 18.6 percent to 39.8 percent, and conversion during the first eight hours climbed from 8.0 percent to 25.4 percent [5]. Bacterial genes involved in glucoraphanin conversion tracked with how well each person responded.
This is the most direct human evidence on the question that matters most to a buyer: add the enzyme, and more compound shows up.
Why Standard Broccoli Supplements Underperform Fresh Sprouts
Two crossover studies from the same research group compared fresh broccoli sprouts with conventional broccoli supplements, one of them matched for glucosinolate content. Both found bioavailability dramatically lower from the supplements, with plasma and urinary peaks arriving later [6][7].
The food supply has the same weakness. A study comparing fresh with commercially frozen broccoli found bioavailability about tenfold higher from the fresh soups, attributed to myrosinase destroyed during commercial blanching and freezing [8].
Freshness and enzyme activity travel together. Processing is what breaks them apart.
Delayed peaks matter for a practical reason. A compound that arrives later and in smaller amounts gives your body less to work with at any one moment, and it makes the timing of a supplement around meals far harder to predict.
What Is Actually Inside the Capsule Types
Capsules are not an automatic win either. The delivery format changes how much of the enzyme survives the trip.
Stomach acid inhibits myrosinase. A pilot study that tracked participants before and after starting a proton pump inhibitor showed that gastric acidity appears to attenuate glucoraphanin bioavailability, and that enteric coating improved conversion, most likely by sparing myrosinase from stomach acid [9]. The same study found that higher body mass tracked with lower conversion efficiency.
An in vitro digestion model, not a human trial, then compared encapsulation with loose powder. Encapsulated broccoli seed extract combined with mustard seed powder at a 4 to 1 ratio converted at 72.1 percent, against 29.3 percent for free powder [10]. Adding ascorbic acid improved conversion further.
That last result comes from a laboratory model of digestion, so treat the size of the gap as directional rather than as a number you would personally see.
Read together, the pattern is consistent. The format that performs best delivers the precursor and a protected enzyme source to the intestine together, not to the stomach.
How Much Sulforaphane Per Day and What Trials Dosed
This is where the honest answer is uncomfortable. There is no established sulforaphane dosage, because the trials measured different things in different groups of people.
The phase I safety study assigned three cohorts 25 micromoles of glucoraphanin, 100 micromoles of glucoraphanin, or 25 micromoles of isothiocyanate, dosed every eight hours for seven days. Recovery as a fraction of dose was 17.8 percent, 19.6 percent, and 70.6 percent respectively [11].
The preformed isothiocyanate arm recovered far more than either glucoraphanin arm at the same nominal amount. In familiar units, 25 micromoles of glucoraphanin works out to about 11 milligrams, and 100 micromoles to about 44 milligrams.
A separate protocol gave 200 micromoles per day and split it into two 100 micromole doses twelve hours apart. The split schedule held higher plasma metabolite levels at later time points than a single daily dose [12].
That split is the practical basis for a twice-daily routine rather than one large morning dose.
Where the Evidence Runs Out
Absorption is well documented. Measured benefit in a person is not, and you deserve to know that before you spend money.
In an 89-patient randomized, double-blind, placebo-controlled trial, participants took 25 micromoles or 150 micromoles of sulforaphane daily for four weeks. The compound was absorbed, and both doses were well tolerated. Nrf2 target gene expression showed no consistent pattern of change across the groups, and neither inflammation measures nor lung-function measures differed from placebo [13].
The split-dose study reached a similar conclusion on molecular targets. No dose response was observed for heme oxygenase-1, histone deacetylase activity, or p21 [12].
A review of the field explains why this is not surprising. After more than 50 clinical trials examining absorption and downstream effects, the field still lacks validated human biomarkers of effect [1].
Switching on a pathway in a laboratory is not the same thing as producing a measured benefit in a person.
None of this makes sulforaphane worthless. The absorption data is solid and the mechanism is real. It means the defensible claim is narrower than the marketing: a well-formulated product supports the body's own antioxidant and detoxification enzyme systems, and how that shows up for you individually is not yet something a blood test can predict.
Is Sulforaphane Safe
Tolerability across the human trials has been good. The phase I study ran 32 hematology and chemistry tests before, during, and after dosing and reported no concerning changes [11].
The long-standing worry about cruciferous vegetables and the thyroid has now been tested directly. A 12-week randomized trial in 45 women found no effect on TSH, free thyroxine, thyroglobulin, or thyroid autoimmunity status [14]. That is a clearer answer than the vague caution usually repeated about this family of vegetables.
One real caution remains. Laboratory research shows sulforaphane can modulate the drug-metabolism enzyme system that clears many medications [15]. Because that system handles so many prescriptions, clear any new supplement with your prescriber before you start.
Staying near the amounts used in the human studies is also a reasonable instinct, since those doses are the ones with the most human safety data behind them [11].
How to Read a Sulforaphane Label
Bring these five questions to any product page.
- Count glucoraphanin, not broccoli powder. The precursor amount is the only number that tells you how much convertible material you are getting.
- Look for a stated myrosinase source. It may be mustard seed powder or a named enzyme. If the label never mentions the enzyme, the conversion is being handed to your gut bacteria.
- Prefer a capsule or an enteric-coated form over loose powder. Stomach acid works against myrosinase, and a coating can spare it [9][10].
- Look for a named extract standardized to a percentage. A standardized broccoli sprout extract tells you what you are actually buying.
- Ignore equivalent to X pounds of broccoli. That phrase describes plant material, not delivered compound, and it converts nothing on its own.
Those five questions also answer the best sulforaphane supplement question for you. The strongest option states its glucoraphanin amount, names its myrosinase source, and puts both in a form that survives the stomach.
Units are the last trap. Some labels print micrograms, some print milligrams, and some print micromoles, and the three are easy to confuse at a glance. Convert everything to milligrams before you compare: micrograms divided by 1,000 gives milligrams. The trial doses of 25 and 100 micromoles of glucoraphanin land at about 11 milligrams and about 44 milligrams.
How to Think About the Purchase
You are not choosing between sulforaphane and nothing. You are choosing between a product that delivers the compound and one that asks your gut bacteria to build it on the spot.
The evidence supports a simple preference order: an enzyme-active preparation first, a capsule over loose powder second, and a clear glucoraphanin number over vague broccoli language third.
Agape Nutrition carries professional-grade options in this category, including formulas that pair a broccoli seed extract with a myrosinase source, so you can compare products against the five questions above instead of against a marketing claim.
Buy the enzyme, not the broccoli count. That is the whole decision.
What We Recommend
Three options below answer the label questions above. Each one names its myrosinase source rather than leaving the conversion to gut bacteria, and each was verified live and in stock on October 8, 2026 at the price shown.
XYMOGEN, OncoPLEX Plus Myrosinase 30 Capsules
The enzyme-active option, a broccoli seed extract paired with a named myrosinase source so the conversion step is built into the capsule instead of being outsourced to gut bacteria.
$54.99
XYMOGEN, ActivEssentials with OncoPLEX & D3 60 Packets
A daily packet system that carries the OncoPLEX broccoli component alongside a broader foundational blend with vitamin D3, for readers who want the daily basics and the cruciferous material in one product.
$117.99
Allergy Research Group, Nrf2 Renew 120 Veg Capsules
A vegetarian capsule that approaches antioxidant support through the Nrf2 pathway the body already uses, offered as a non-broccoli format for readers who want a different route to the same enzyme systems.
$75.39
References
- Yagishita Y, Fahey JW, Dinkova-Kostova AT, Kensler TW. Broccoli or Sulforaphane: Is It the Source or Dose That Matters? Molecules. 2019. https://pubmed.ncbi.nlm.nih.gov/31590459/
- Fahey JW, Holtzclaw WD, Wehage SL, Wade KL, Stephenson KK, Talalay P. Sulforaphane Bioavailability from Glucoraphanin-Rich Broccoli: Control by Active Endogenous Myrosinase. PLoS One. 2015. https://pubmed.ncbi.nlm.nih.gov/26524341/
- Egner PA, Chen JG, Wang JB, Wu Y, Sun Y, Lu JH, et al. Bioavailability of Sulforaphane from two broccoli sprout beverages: results of a short-term, cross-over clinical trial in Qidong, China. Cancer Prev Res (Phila). 2011. https://pubmed.ncbi.nlm.nih.gov/21372038/
- Okunade O, Niranjan K, Ghawi SK, Kuhnle G, Methven L. Supplementation of the Diet by Exogenous Myrosinase via Mustard Seeds to Increase the Bioavailability of Sulforaphane in Healthy Human Subjects after the Consumption of Cooked Broccoli. Mol Nutr Food Res. 2018. https://pubmed.ncbi.nlm.nih.gov/29806738/
- Mastaloudis A, Holcomb L, Fahey JW, Sakaguchi CA, Nieman DC, Kay C, et al. Exogenous myrosinase from mustard seed increases bioavailability of sulforaphane from a glucoraphanin-rich broccoli seed extract in a randomized clinical study. Sci Rep. 2026. https://pubmed.ncbi.nlm.nih.gov/41692762/
- Clarke JD, Hsu A, Riedl K, Bella D, Schwartz SJ, Stevens JF, Ho E. Bioavailability and inter-conversion of sulforaphane and erucin in human subjects consuming broccoli sprouts or broccoli supplement in a cross-over study design. Pharmacol Res. 2011. https://pubmed.ncbi.nlm.nih.gov/21816223/
- Clarke JD, Riedl K, Bella D, Schwartz SJ, Stevens JF, Ho E. Comparison of isothiocyanate metabolite levels and histone deacetylase activity in human subjects consuming broccoli sprouts or broccoli supplement. J Agric Food Chem. 2011. https://pubmed.ncbi.nlm.nih.gov/21928849/
- Saha S, Hollands W, Teucher B, Needs PW, Narbad A, Ortori CA, et al. Isothiocyanate concentrations and interconversion of sulforaphane to erucin in human subjects after consumption of commercial frozen broccoli compared to fresh broccoli. Mol Nutr Food Res. 2012. https://pubmed.ncbi.nlm.nih.gov/23109475/
- Fahey JW, Wade KL, Stephenson KK, Panjwani AA, Liu H, Cornblatt G, et al. Bioavailability of Sulforaphane Following Ingestion of Glucoraphanin-Rich Broccoli Sprout and Seed Extracts with Active Myrosinase: A Pilot Study of the Effects of Proton Pump Inhibitor Administration. Nutrients. 2019. https://pubmed.ncbi.nlm.nih.gov/31261930/
- Zhu W, Cremonini E, Mastaloudis AF, Mitchell AE, Bornhorst GM, Oteiza PI. Optimization of sulforaphane bioavailability from a glucoraphanin-rich broccoli seed extract in a model of dynamic gastric digestion and absorption by Caco-2 cell monolayers. Food Funct. 2025. https://pubmed.ncbi.nlm.nih.gov/39670818/
- Shapiro TA, Fahey JW, Dinkova-Kostova AT, Holtzclaw WD, Stephenson KK, Wade KL, et al. Safety, tolerance, and metabolism of broccoli sprout glucosinolates and isothiocyanates: a clinical phase I study. Nutr Cancer. 2006. https://pubmed.ncbi.nlm.nih.gov/16965241/
- Atwell LL, Hsu A, Wong CP, Stevens JF, Bella D, Yu TW, et al. Absorption and chemopreventive targets of sulforaphane in humans following consumption of broccoli sprouts or a myrosinase-treated broccoli sprout extract. Mol Nutr Food Res. 2015. https://pubmed.ncbi.nlm.nih.gov/25522265/
- Wise RA, Holbrook JT, Criner G, Sethi S, Rayapudi S, Sudini KR, et al. Lack of Effect of Oral Sulforaphane Administration on Nrf2 Expression in COPD: A Randomized, Double-Blind, Placebo Controlled Trial. PLoS One. 2016. https://pubmed.ncbi.nlm.nih.gov/27832073/
- Chartoumpekis DV, Ziros PG, Chen JG, Groopman JD, Kensler TW, Sykiotis GP. Broccoli sprout beverage is safe for thyroid hormonal and autoimmune status: Results of a 12-week randomized trial. Food Chem Toxicol. 2019. https://pubmed.ncbi.nlm.nih.gov/30735751/
- Lubelska K, Milczarek M, Modzelewska K, Krzysztoń-Russjan J, Fronczyk K, Wiktorska K. Interactions between drugs and sulforaphane modulate the drug metabolism enzymatic system. Pharmacol Rep. 2012. https://pubmed.ncbi.nlm.nih.gov/23238480/
Frequently Asked Questions
Does myrosinase really matter in a sulforaphane supplement?
Yes, and it is the most consequential line item in the formula. Glucoraphanin is a precursor, and it needs myrosinase to become sulforaphane. When the enzyme is active and present, the compound is 3 to 4 times more bioavailable than the same amount of glucoraphanin delivered without it [2]. When it is missing, your gut bacteria become the conversion step, and bacterial conversion varies a great deal from one person to the next. In a 16-person randomized crossover, adding mustard-seed myrosinase to a broccoli seed extract doubled bioavailability from 18.6 percent to 39.8 percent [5].
How much sulforaphane per day should I take?
There is no officially established daily amount. The clinical studies used a range rather than one target. The phase I safety study dosed 25 and 100 micromoles of glucoraphanin, which works out to about 11 milligrams and about 44 milligrams, along with 25 micromoles of preformed isothiocyanate, every eight hours for seven days [11]. Another protocol used 200 micromoles per day split into two 100 micromole doses twelve hours apart, and that split schedule held higher plasma levels at later time points than a single daily dose [12]. If you want a starting point that mirrors the human work, twice daily with food is better supported than one large dose.
What is the difference between glucoraphanin and sulforaphane?
Glucoraphanin is the storage form found in the plant. Sulforaphane is what it becomes after myrosinase acts on it. The distinction matters because the two behave very differently in the body. In a 50-person crossover trial, a sulforaphane-rich beverage produced a mean urinary recovery of 70 percent of the dose, while a glucoraphanin-rich beverage produced a mean of 5 percent [3]. A bottle that lists glucoraphanin and nothing else is selling you the starting material.
Is a broccoli sprout extract better than broccoli powder?
It depends entirely on how the extract was made. What matters is whether myrosinase survived or was added back. Two crossover studies from the same research group found bioavailability dramatically lower from conventional broccoli supplements than from fresh sprouts, with peaks arriving later [6][7]. Look for a named extract standardized to a percentage and a stated myrosinase source. General broccoli powder language tells you nothing about enzyme activity.
Can I just eat broccoli instead of taking a supplement?
Fresh raw sprouts are an excellent source, but cooked and frozen broccoli is unreliable. Cooking destroys myrosinase, and a study comparing fresh with commercially frozen broccoli found bioavailability about tenfold higher from the fresh soups because the freezing process had destroyed the enzyme [8]. If you eat cooked broccoli, adding a small amount of powdered mustard seed, a myrosinase source, raised mean urinary SF-NAC from 9.8 to 44.7 micromoles per gram of creatinine, over four times [4]. A supplement is simply a way to get a measured amount in a form you will actually take consistently.
Does sulforaphane affect thyroid function?
The concern comes from the broader cruciferous vegetable family, and it has been tested directly. A 12-week randomized trial in 45 women found no effect on TSH, free thyroxine, thyroglobulin, or thyroid autoimmunity status [14]. If you have a diagnosed thyroid condition or take thyroid medication, mention any new supplement to your prescriber. The specific worry about this compound and thyroid hormones was not borne out in that trial, though one 12-week study is not the last word.