What Is The Best Sulforaphane Supplement?

Written by David Roberts, MPH · Co-Founder, Mara Labs

What Does Bioavailability Mean for a Sulforaphane Supplement?

Bioavailability is the share of a labeled dose that reaches your bloodstream and your cells in a form they can use. For sulforaphane, that number is the entire question.

The reason is simple. Most products sold as sulforaphane supplements do not contain sulforaphane.

They contain glucoraphanin — sometimes printed on the label as "sulforaphane glucosinolate" or "broccoli sprout extract." Glucoraphanin is the precursor. It is biologically inactive until an enzyme converts it.

The pharmacokinetics have been characterized in detail. Upwards of 70 percent of an administered sulforaphane dose is recovered as thiol conjugates in urine. For glucoraphanin, that figure is about 10 percent, with a slower elimination phase reflecting poor and highly variable conversion. [2]

Same shelf. Same category. A sevenfold difference in what your cells receive.

What Are the Three Ways to Get Sulforaphane Into the Body?

There are three, and they are not interchangeable. Each one asks your body to do a different amount of work before the active compound exists.

Glucoraphanin alone. Broccoli sprout powders and most capsule extracts. Conversion depends entirely on myrosinase-like activity from your gut bacteria in the colon.

Glucoraphanin plus myrosinase. Beverages and capsules that supply the enzyme alongside the precursor. Better on paper, with a durability problem covered further down.

Pre-formed or stabilized sulforaphane. The active molecule delivered directly. No enzyme required, no bacterial conversion, no dependency on the state of your microbiome that week.

These figures come from controlled research settings. [2][3] Real-world shipping, storage, heat exposure, and individual gut conditions push the precursor numbers down further, not up.

Who Is Jed Fahey and Why Does His Research Matter Here?

Jed Fahey, PhD, is a nutritional biochemist at Johns Hopkins University and director of its Brassica Chemoprotection Laboratory. His lab did the foundational work characterizing how compounds in cruciferous vegetables reach and act on human cells.

His 2015 paper in PLoS ONE is the one that matters for this question. The title states the finding: sulforaphane bioavailability from glucoraphanin-rich broccoli is controlled by active endogenous myrosinase. [6]

That design isolated the single variable everyone else was glossing over. Not how much glucoraphanin is in the product — whether the enzyme needed to convert it is still functional when it arrives.

His group also established why sprouts became the reference source at all: three-day germinated broccoli seed contains 20 to 50 times more glucoraphanin than mature broccoli. [3]

Why Does the Same Supplement Work Differently in Different People?

Because conversion is a biological process, not a chemical constant. Two people can take an identical glucoraphanin dose and produce sulforaphane levels that differ by an order of magnitude.

Four variables drive most of that spread.

Gut microbiome composition. Several bacterial genera, including Bifidobacterium, Lactobacillus, and Bacteroides, can hydrolyze glucosinolates. Their populations vary enormously between individuals. [5]

Stomach acidity. Higher acid degrades both glucoraphanin and plant-derived myrosinase before either reaches the small intestine, where absorption is most efficient.

Heat and processing. Blanching or microwaving broccoli inactivates myrosinase and sharply reduces the sulforaphane that reaches plasma. The same physics applies to heat-processed supplement ingredients. [5]

Genetics. Polymorphisms in GSTM1 and GSTT1 — genes encoding a detoxifying glutathione-S-transferase — shift how isothiocyanates are processed and excreted. [5]

The consequence is worth stating plainly. The dose printed on a glucoraphanin label is not the dose your body receives, and there is no way to know your own conversion rate without measuring it.

Why Do Label Claims Overstate What You Receive?

Because many of them are arithmetic, not measurement. The number on the bottle is often a calculated ceiling that assumes a perfect conversion that never happens in a human body.

The industry term is "sulforaphane potential." A lab measures the glucoraphanin content, multiplies it by 0.406 to account for relative molecular weights, and prints the result. No provision is made for whether myrosinase survived processing. [4]

A second problem compounds it. Epithiospecifier protein, or ESP, redirects the reaction toward nitriles instead of isothiocyanates. Where ESP has not been fully deactivated, the potential figure overstates the yield again. [4]

A third: some assays add exogenous myrosinase to force complete conversion in the test tube. The result reads well and tells you nothing about what the capsule does on its own. [4]

Assays that rely on the enzyme the product retained after processing produce lower numbers — and more closely approximate what happens in human physiology. [4]

Why Doesn't Adding Myrosinase to the Capsule Fix It?

Because the enzyme rarely survives the trip. Myrosinase is a protein, and stomach acid treats it the way it treats any other protein.

It is also fragile on the shelf. Enzyme activity drops with heat, moisture, and age, so a capsule that tested well at manufacture may test very differently after a summer in a distribution warehouse.

Timing works against it too. When conversion happens late, in the colon rather than the small intestine, absorption is slower and less complete.

The clinical record reflects this. One trial tested a broccoli supplement containing glucoraphanin with no active myrosinase and produced no statistically significant results — gut-mediated conversion was too unpredictable to generate consistent outcomes across the study population. [3]

Some participants converted efficiently. Most did not.

What Does Stabilized Sulforaphane Change?

It removes the conversion step entirely. There is no precursor to hydrolyze, no enzyme to protect, and no bacterial population to depend on.

Sulforaphane's own properties are what make this work once it is delivered intact. It is a small molecule, molecular weight 177.29, and lipophilic — it dissolves in fat and crosses cell membranes to reach intracellular targets directly. [3]

Absolute bioavailability has been demonstrated at around 80 percent, with plasma concentrations peaking roughly one hour after ingestion. Polyphenols, by comparison, typically run 1 to 8 percent. [3]

The engineering challenge is that the same chemical reactivity making sulforaphane biologically potent also makes it unstable in a bottle. Stabilization means solving that without altering the molecule responsible for the activity.

Has Stabilized Sulforaphane Been Shown to Activate Nrf2 in People?

Yes. That distinction — measured activation versus assumed potential — is the one we set out to test directly in 2023.

Nrf-2 is the transcription factor governing the body's antioxidant response, a network of more than 200 genes. Sulforaphane binds KEAP1, which releases Nrf-2 into the nucleus, where it drives expression of genes including glutathione synthetase. [8]

We measured glutathione induction in HepG2 liver cells as an indirect readout of Nrf-2 activity, comparing four sulforaphane products against a leading glucoraphanin product. [8]

The second arm moved from cells in a dish to people. Buccal cells were collected by cheek swab at baseline, then again two hours after a single 10 mg serving. BrocElite® Plus induced Nrf-2 directly in vivo. Stabilized Sulforaphane Brand #1 did not. [8]

A separate study looked at the inflammatory side. Six participants abstained from supplements and cruciferous vegetables for seven days, then provided urine samples across three days with a placebo and a 10 mg dose. The 10 mg serving reduced interleukin-6 by an average of 28 percent in 24 hours. [9]

This is what separates a mechanism claim from a marketing claim. Any brand can print a milligram figure. Showing that the pathway turns on requires measuring it.

"Sulforaphane is notoriously unstable. Our naturally stabilized capsule delivers 5 mg of already-converted sulforaphane — roughly equivalent to 2.5 pounds of mature broccoli — to activate NRF2. Combined with synergistic isothiocyanates, it can drive NRF2 activity up to fivefold versus sulforaphane alone."

— Dr. John Gildea, PhD, Co-Founder & Chief Science Officer

How Do You Evaluate a Sulforaphane Supplement Before You Buy?

Five questions separate a real product from a well-designed label. Ask them in this order.

1. Does it contain sulforaphane or glucoraphanin? "Sulforaphane glucosinolate" and "broccoli sprout extract" both mean the precursor. A product containing the active compound will say so explicitly.
2. Is the number measured or calculated? A "potential" or "yield" figure is arithmetic performed on glucoraphanin content, not an assay of what the capsule delivers.
3. Can the brand show Nrf2 activation? Bioactivity in a test tube is not the same as pathway activation in a cell. If a company implies one from the other, treat it as a red flag.
4. What is in it besides the active compound? Ask about solvents, flow agents, and fillers. Ask whether every batch is third-party tested for content, glyphosate, heavy metals, and contaminants.
5. Who formulated it, and why? There is a difference between a company that solved a delivery problem and a company that found a category.

Which Delivery Option Makes Sense for You?

It depends on how much variability you are willing to accept. Both routes are legitimate; they are not equivalent.

If you enjoy the ritual — growing sprouts, juicing, mixing powders — that route can be rewarding. It asks for daily prep, cold storage, careful timing once the enzyme meets moisture, and acceptance of batch-to-batch swings.

If what you want is the same dose reaching your cells every day, without your microbiome casting a vote, stabilized sulforaphane is the more dependable tool.

We did not invent sulforaphane. Johns Hopkins researchers isolated it in 1992, and more than 2,000 papers have followed. [1]

We stabilized it, so the dose on the label is the dose your cells receive.

Frequently Asked Questions About Sulforaphane Bioavailability

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult a healthcare professional before beginning any new supplement, especially if you are pregnant, nursing, taking medication, or managing a condition. Individual results may vary.