Sulforaphane Bioavailability: Myrosinase, Absorption & What Reaches the Body

Sulforaphane bioavailability is not a fixed number. The amount that reaches systemic circulation depends on what you ingest—preformed sulforaphane, glucoraphanin paired with active myrosinase, glucoraphanin without active enzyme, or a food whose preparation preserved or destroyed myrosinase.

That distinction is the reason two products can display impressive broccoli-extract milligram numbers yet deliver very different sulforaphane exposure. Human studies repeatedly show that conversion is part of the dose.

What does “sulforaphane bioavailability” mean?

Most human sulforaphane studies do not directly measure every molecule entering every tissue. Instead, they estimate exposure by measuring sulforaphane and its dithiocarbamate metabolites—often in urine over 8–24 hours after dosing. That gives a useful measure of how much administered precursor or sulforaphane was converted, absorbed and metabolized.

Because formulations and measurement methods differ, a bioavailability percentage from one trial should not be pasted onto another supplement label. The useful question is comparative: which delivery systems consistently produce more—and less variable—human exposure?

The four delivery systems that matter

Preformed sulforaphane vs glucoraphanin: the clearest human comparison

A randomized crossover study in 50 healthy adults compared a glucoraphanin-rich broccoli sprout beverage with a sulforaphane-rich beverage made by enzymatically converting the precursor before ingestion. Average urinary bioavailability was about 70% with the sulforaphane-rich preparation versus about 5% with the glucoraphanin-rich preparation.^[1]

The important lesson is not that every preformed sulforaphane product is exactly 70% bioavailable. It is that removing the uncertain precursor-conversion step can dramatically change delivered exposure.

Active myrosinase changes the conversion equation

Glucoraphanin is a stable precursor. Myrosinase is the enzyme that hydrolyzes it into sulforaphane. When a preparation contains no active plant myrosinase, conversion depends heavily on the gut microbiome and varies widely between people.

In human work comparing glucoraphanin-rich preparations, formulations without active myrosinase averaged roughly 10% conversion, while preparations supplying active myrosinase produced approximately 30–40% conversion and reduced variability.^[2]

The newest randomized crossover study in our Data Center reinforces that pattern. Sixteen healthy adults received broccoli seed extract with or without mustard-seed myrosinase. Average sulforaphane bioavailability rose from 18.6% without added myrosinase to 39.8% with it.^[3]

This is why a supplement stating only “broccoli seed extract” or “glucoraphanin” gives you incomplete information. You also want to know whether active myrosinase is present and whether its activity is preserved through manufacturing and storage.

Fresh sprouts can outperform a myrosinase-inactivated supplement

A crossover study compared fresh broccoli sprouts with a broccoli supplement containing glucoraphanin but lacking active plant myrosinase. Fresh sprouts produced markedly higher and faster sulforaphane exposure.^[4]

That does not mean “food always beats supplements.” It means enzyme-active food can outperform an enzyme-inactive precursor supplement. A well-designed glucoraphanin + active-myrosinase supplement is a different formulation class.

Raw vs cooked broccoli: preparation changes what reaches the body

Human trials show that cooking can sharply change sulforaphane exposure because heat can inactivate plant myrosinase. Raw broccoli produced higher and faster sulforaphane bioavailability than cooked broccoli in a controlled crossover study.^[5]

Commercial freezing can have a similar effect because broccoli is commonly blanched before freezing. In an 18-person randomized crossover study, lightly cooked fresh broccoli produced approximately tenfold greater sulforaphane bioavailability than similarly prepared commercial frozen broccoli, with the difference attributed largely to myrosinase destruction during commercial blanching.^[6]

This does not mean every frozen broccoli product is equivalent to the product tested. Processing methods differ, and the study measured acute pharmacokinetics rather than a long-term health outcome.

Can you restore myrosinase after cooking?

Yes—at least experimentally. A randomized human study found that adding mustard seed, which supplies active myrosinase, to cooked broccoli significantly increased sulforaphane bioavailability.^[7]

This gives the food literature the same basic message as the supplement literature: the precursor is only half of the system.

Does stomach acid destroy myrosinase?

Gastric conditions are another formulation variable. A Johns Hopkins pilot study used Avmacol, a glucoraphanin + active-myrosinase supplement, to compare conversion under normal gastric acidity and during proton-pump-inhibitor use, and also compared enteric-coated with uncoated tablets.^[8]

Overall conversion from the active-myrosinase product was around one-third of the glucoraphanin dose. Enteric coating improved conversion under normal gastric acidity by about 28%, but it also produced more gastrointestinal discomfort and did not improve conversion during proton-pump-inhibitor treatment.

Editorial interpretation: gastric delivery can matter, but “enteric coated” is not a universal quality badge. The entire system—precursor content, enzyme activity, release location, tolerability and actual human conversion—matters.

What role does the gut microbiome play?

When active plant myrosinase is absent, some gut bacteria can hydrolyze glucoraphanin. The problem is that microbial conversion is highly variable. In the 2026 crossover study, several bacterial genes correlated with glucoraphanin conversion, but adding a defined myrosinase source still approximately doubled average bioavailability.^[3]

So “your gut bacteria will convert it” is biologically plausible but not equivalent to reliable delivery.

How quickly is sulforaphane absorbed and cleared?

Sulforaphane is absorbed and metabolized relatively quickly. Across human pharmacokinetic studies, plasma concentrations generally peak within a few hours and most urinary metabolite recovery occurs within the first day. The exact timing shifts with direct sulforaphane versus precursor delivery because glucoraphanin must first be converted.

That difference explains why precursor-only formulations can produce slower and more prolonged exposure while preformed sulforaphane produces a faster peak. Neither pattern is automatically superior for every biological target.

How to read a sulforaphane supplement label for bioavailability

1. Identify the active starting material. Is the label disclosing sulforaphane, glucoraphanin, “sulforaphane glucosinolate,” or only broccoli-extract weight?
2. Look for active myrosinase. If the product is glucoraphanin-based, this is one of the strongest formulation variables supported by human data.
3. Do not convert extract milligrams into sulforaphane milligrams. They are not equivalent units.
4. Look for lot-level or assay transparency. A brand should ideally show what was measured rather than rely on raw-material marketing.
5. Separate formulation evidence from outcome evidence. Better bioavailability proves better delivery—not better longevity, cancer prevention or disease treatment.

Bioavailability vs dose: why these are different questions

Suppose two products each provide the same nominal glucoraphanin dose. If one depends on gut bacteria and the other supplies active myrosinase, the delivered sulforaphane exposure may differ substantially. That is why our sulforaphane dosage guide treats “administered dose” and “delivered dose” as separate concepts.

For the chemistry behind the conversion step, see Myrosinase & Sulforaphane. For product selection, see our best sulforaphane supplements guide.

Bottom line

The best-supported rule in sulforaphane supplementation is that formulation is part of the dose. Preformed sulforaphane bypasses precursor conversion. Glucoraphanin paired with active myrosinase consistently produces more and less-variable sulforaphane exposure than glucoraphanin alone. Food preparation, gastric delivery and individual microbiome differences can further change the result.

That makes bioavailability the first question to answer before interpreting any claim about benefits, dosage or product superiority.