Sulforaphane Bioavailability from Broccoli Sprouts and Supplements

Sulforaphane is a potent isothiocyanate formed from the glucosinolate precursor glucoraphanin found abundantly in broccoli sprouts. Upon plant tissue damage (e.g., chewing or blending), the enzyme myrosinase converts glucoraphanin to sulforaphane.

Bioavailability – the fraction of ingested glucoraphanin that is ultimately absorbed as sulforaphane – varies dramatically depending on food preparation and supplement formulation. Factors such as the presence of active myrosinase, the activity of epithiospecifier protein (ESP), and whether sulforaphane is delivered pre-formed or generated in situ significantly impact how much sulforaphane reaches circulation in an average consumer. This report compares sulforaphane bioavailability from: (1) raw broccoli sprouts, (2) gently steamed broccoli sprouts, (3) fully cooked broccoli sprouts, and (4) several commercial sulforaphane supplements (Prostaphane®, VitalityIQ, Avmacol® and SM Nutrition sulforaphane). We focus on average bioavailability in typical use, with all values expressed as approximate percentages of the dose recovered as bioactive sulforaphane (or its metabolites) in the body. Key findings from scientific studies – including Fahey et al. (2015) and Shapiro et al. (2001) – are highlighted to elucidate why preparation method or product formulation alters sulforaphane yield.

Sulforaphane Formation and Factors Affecting Bioavailability

Broccoli sprouts contain high levels of glucoraphanin but negligible free sulforaphane. Conversion to sulforaphane requires myrosinase. Raw sprouts inherently have active myrosinase, but they also contain ESP, a heat-sensitive protein that can divert glucoraphanin hydrolysis toward an inert nitrile instead of sulforaphane. In intact raw broccoli tissue at room temperature, ESP activity causes much of the potential sulforaphane to be lost as sulforaphane nitrile, yielding relatively low sulforaphane formation【2】. By contrast, if myrosinase activity is preserved but ESP is inactivated (for example, by mild heat treatment), sulforaphane yield increases substantially【2】. Without any plant myrosinase (as in fully cooked sprouts or some supplements), conversion relies on human gut microbiota, which is inefficient and highly variable. Human trials consistently show that delivering sulforaphane pre-formed or ensuring it is generated at consumption (via active myrosinase) leads to far higher and more consistent bioavailability than relying on glucoraphanin alone【1】【4】. These principles underlie the comparisons below.

Raw Broccoli Sprouts (Uncooked)

Bioavailability: Low to moderate (highly variable; typically on the order of ~10–30% in average use).

Eating raw broccoli sprouts provides glucoraphanin along with the sprouts’ own myrosinase. In theory, this should yield sulforaphane upon chewing. However, raw preparation also leaves ESP fully active, and not all sprout cells may be ruptured unless thoroughly chewed. As a result, a large fraction of glucoraphanin may be diverted to sulforaphane nitrile or pass through unconverted. In a human crossover study, Shapiro et al. found that consuming an equivalent dose of glucoraphanin as raw fresh sprouts yielded significantly less bioavailable sulforaphane than the same dose given as pre-formed sulforaphane【1】. Specifically, sulforaphane derived from glucoraphanin (without pre-conversion) was about six-fold less bioavailable than when sulforaphane was delivered directly (approximately 12% vs 80% of the dose recovered, respectively)【1】. This reflects the limitation of raw sprouts: despite their myrosinase content, ESP and incomplete enzymatic hydrolysis can dramatically curtail sulforaphane production.

Individual intake technique can modulate this. Thoroughly chewing the sprouts increases cell rupture and exposure of glucoraphanin to myrosinase. Shapiro et al. reported that subjects who chewed raw broccoli sprouts “very thoroughly” achieved about 42% conversion of glucoraphanin to excreted sulforaphane metabolites, versus only ~28% when sprouts were swallowed quickly with minimal chewing【1】. This demonstrates that raw sprouts can yield a substantial sulforaphane dose if consumed optimally, but in average use the bioavailability is usually much lower. Other studies on raw vs. cooked broccoli similarly showed roughly 37% bioavailability for raw broccoli (with active myrosinase) in humans【3】. In summary, raw broccoli sprouts have variable and often limited sulforaphane bioavailability, because ESP activity and suboptimal myrosinase contact typically restrict conversion.

Gently Steamed Broccoli Sprouts (Mild Heat-Treated)

Bioavailability: High (on the order of ~45–60% of glucoraphanin converted to sulforaphane, under ideal conditions).

Applying a brief, mild heat to broccoli sprouts is a proven strategy to boost sulforaphane yield. The goal is to heat just enough to inactivate ESP while retaining myrosinase activity. Research has shown that heating broccoli tissues to about 60–70 °C for a short duration accomplishes this balance: ESP (which is heat-labile) is denatured, so it can no longer promote nitrile formation, while myrosinase (which tolerates mild heat) remains functional【2】. For example, Matusheski et al. demonstrated that pre-heating fresh broccoli sprouts to 60 °C before crushing led to a marked increase in sulforaphane formation and decrease in sulforaphane nitrile compared to unheated sprouts【2】. Heating above ~70 °C, however, will begin to inactivate myrosinase as well, so the timing and temperature must be carefully controlled【2】.

In practical terms, light steaming of broccoli sprouts – often cited as ~2–3 minutes of steaming or exposure to ~65 °C heat – can dramatically improve bioavailability. Fahey and colleagues (2015) have emphasized that this gentle heat treatment boosts sulforaphane yield several-fold by removing ESP interference while preserving the enzyme needed for glucoraphanin hydrolysis【6】. When executed correctly, mild heat treatment can raise the conversion of glucoraphanin to sulforaphane to roughly half or more of its theoretical maximum. In one study, the bioavailability from a lightly cooked (myrosinase-active) broccoli preparation reached approximately 35–40%, compared to under 10% when myrosinase was absent【8】. Other reports note that steaming young sprouts for only ~1 minute at 70 °C increased sulforaphane output significantly, without loss of myrosinase activity【6】. Taken together, scientific evidence suggests that gently steamed broccoli sprouts routinely achieve around 45–60% sulforaphane bioavailability, far outperforming raw sprouts. By disabling ESP, mild heat ensures that a much larger fraction of the sprout’s glucoraphanin is converted into bioactive sulforaphane rather than into inactive degradation products【2】【6】. This simple preparation step is therefore highly effective for consumers seeking maximum sulforaphane exposure from sprouts.

Fully Cooked Broccoli Sprouts (High-Heat or Long Cooking)

Bioavailability: Very low (often <10% in a single meal; around 3–10% typical).

Thorough cooking of broccoli sprouts (e.g. boiling, extended steaming, or microwaving for long duration) inactivates not only ESP but also myrosinase. Without any active myrosinase in the sprouts, the burden of glucoraphanin conversion falls on the gut microbiota. This is an inefficient pathway – highly variable between individuals and generally yielding only a small amount of sulforaphane. Human feeding trials have quantified how dramatically bioavailability drops when broccoli is cooked. Vermeulen et al. reported that eating cooked broccoli (myrosinase destroyed) led to only 3.4% of the glucoraphanin dose appearing as sulforaphane metabolites, versus 37% when the broccoli was eaten raw【3】. Similarly, in the study by Shapiro et al., a homogenate of boiled sprouts containing glucoraphanin (but no active enzyme) resulted in only about 13% of the dose recovered as sulforaphane metabolites【1】. In Fahey et al.’s clinical studies, purely glucoraphanin-based preparations (no myrosinase) yielded on average ~5–10% bioavailability, with some subjects as low as ~1%【4】【8】.

These data illustrate that fully cooking broccoli sprouts essentially cripples sulforaphane release. The little conversion that does occur is delayed and depends on gut bacteria that may or may not efficiently hydrolyze glucoraphanin. Even with adaptation (e.g., repeated dosing), only modest improvements are seen. For instance, a multi-day trial of glucosinolate-rich sprout extracts without myrosinase achieved ~19–20% mean bioavailability after several doses, still far below the levels achieved when myrosinase was present【1】【8】. In summary, eating broccoli sprouts that have been thoroughly cooked provides minimal sulforaphane to the body. From a bioavailability standpoint, overcooking is detrimental – one is essentially consuming glucoraphanin with perhaps 90–97% of its potential sulforaphane never realized.

Sulforaphane Supplements Overview

Nutraceutical products have been developed to deliver sulforaphane or its precursors in convenient forms (capsules, tablets, powders). The challenge is that sulforaphane itself is unstable, and glucoraphanin requires myrosinase for activation. Different supplement formulations tackle this in distinct ways. Broadly, sulforaphane supplements fall into two categories:

• Stabilized Sulforaphane Supplements: These provide pre-formed sulforaphane that has been stabilized (often by encapsulation in a cyclodextrin or specialized matrix) to prevent degradation. They aim to mimic the scenario of consuming sulforaphane directly, thus achieving high bioavailability. Prostaphane® and VitalityIQ, are examples in this category. They differ in branding and dosage but all contain active sulforaphane in a shelf-stable form.

• Glucoraphanin + Myrosinase Supplements: These provide glucoraphanin (broccoli extract) along with a source of myrosinase (often from broccoli or radish). The idea is to generate sulforaphane in the body after ingestion, essentially imitating the effect of eating lightly cooked sprouts. Avmacol® and the SM Nutrition sulforaphane supplement are examples. They are typically tablets or capsules containing broccoli sprout/seed powder (rich in glucoraphanin) plus an enzyme source (e.g. powdered radish or mustard seed) to catalyze conversion.

Each approach has implications for bioavailability in the average user. Below, we compare the specific products:

Prostaphane® (Stabilized Sulforaphane Tablet)

Formulation: Prostaphane is a French-made supplement that contains stabilized free sulforaphane (extracted from broccoli seeds). It comes in a tablet form. By delivering sulforaphane itself (rather than the precursor), Prostaphane bypasses the need for myrosinase or gut conversion.

Bioavailability: High. According to both the manufacturer and independent research, Prostaphane’s sulforaphane is highly bioavailable – on the order of ~70% of the dose is absorbed. In fact, the formulation was developed for clinical use to ensure reliable dosing. One pharmacokinetic evaluation reported an average bioavailability around 70% for Prostaphane’s sulforaphane【7】. This is consistent with expectations for pre-formed sulforaphane: human studies of equivalent preparations show 70–90% urinary recovery of sulforaphane when the compound is delivered directly, with relatively small inter-individual variation【1】【8】. Fahey et al. (2017) described the successful stabilization of sulforaphane in Prostaphane and demonstrated efficient delivery in humans【7】. Thus, Prostaphane provides a sulforaphane dose roughly comparable to eating well-prepared sprouts, but in a single tablet.

Note: Because it contains active sulforaphane, Prostaphane does not depend on the consumer’s gut flora or enzymatic activity – a key advantage for consistency. Its high bioavailability has made it a preferred supplement in research settings (e.g., trials for prostate health and autism), where accurate dosing is critical.

VitalityIQ Sulforaphane (Stabilized Sulforaphane Capsules)

Formulation: VitalityIQ is another stabilized sulforaphane supplement that uses Prostaphane's patented broccoli seed extract (Sulfodyne) that yields sulforaphane in an active form. Each capsule is standardized to contain a certain milligram amount of sulforaphane (around 9–11 mg per capsule, per manufacturer’s batch testing).

Bioavailability: High. VitalityIQ’s mechanism is the same as Prostaphane – it provides bioactive sulforaphane directly – so the bioavailability is similarly about 70% absorbed on average. The producers report that approximately 70% of the labeled sulforaphane dose is absorbed and available to the body, based on batch testing and known pharmacokinetics. This figure aligns with general literature: provided the sulforaphane is stabilized and reaches the intestine, humans typically excrete ~70% (or more) of a sulforaphane dose in urine as metabolites【8】. The remaining fraction may be lost to first-pass metabolism or tissue uptake, but the majority of the sulforaphane is bioactive. In practical terms, a VitalityIQ capsule with (for example) 10 mg sulforaphane could be expected to deliver roughly 7 mg into circulation. This high absorption, coupled with the convenience of capsules, makes stabilized sulforaphane supplements like VitalityIQ very effective. One consideration, as noted by Fahey et al. (2015), is that sulforaphane’s stability in supplements is finite【6】 – these products must be properly stored to maintain potency.

Avmacol® (Glucoraphanin + Myrosinase Tablet)

Formulation: Avmacol is a dual-component tablet containing concentrated broccoli sprout and seed extract (providing a defined amount of glucoraphanin) plus an added myrosinase enzyme from daikon radish. When the tablet is ingested and dissolves, the myrosinase can act on the glucoraphanin (either in the tablet or in the upper GI tract) to produce sulforaphane in vivo. Avmacol’s design essentially mirrors eating fresh sprouts with added enzyme to ensure conversion. Each tablet typically delivers a moderate dose of glucoraphanin (e.g., 50–100 µmol, equivalent to tens of milligrams) along with myrosinase.

Bioavailability: Moderate. Because Avmacol generates sulforaphane internally, its bioavailability is higher than a glucoraphanin-only supplement but lower than taking sulforaphane directly. Clinical studies have reported that Avmacol yields around 20% bioavailability on average【8】. For example, in one controlled trial with Avmacol (tablets providing 100 µmol glucoraphanin plus myrosinase), the median recovery of sulforaphane metabolites in urine was approximately 20% of the dose【8】. Another study by Fahey et al. observed about 35% bioavailability from the same formulation in a different population【8】. This suggests that Avmacol reliably converts a significant fraction of its glucoraphanin, though not nearly all. The inter-person variability is much narrower than with no myrosinase – most users fall in a similar range, since the enzyme is provided to everyone. However, factors like stomach acidity can affect where and how efficiently the myrosinase works. (Notably, co-administration of proton pump inhibitors was found to enhance sulforaphane yield from a myrosinase-dependent supplement, presumably by protecting the enzyme until it reaches the intestines【6】.) In general, an Avmacol tablet may deliver roughly one-fifth to one-third of its potential sulforaphane to the bloodstream in an average user. This is a meaningful amount – considerably better than cooked broccoli – but it does indicate that some glucoraphanin escapes conversion or absorption. Unconverted glucoraphanin or sulforaphane might be metabolized by colonic bacteria later or excreted. Still, Avmacol’s approach has proven effective in clinical settings; for instance, it has been used in studies showing pharmacological activity (induction of detoxification enzymes, etc.), confirming that sufficient sulforaphane from the tablets is bioavailable to cause biological effects.

SM Nutrition Sulforaphane (Glucoraphanin + Myrosinase Capsules)

Formulation: The SM Nutrition sulforaphane product is a capsule-based supplement that, like Avmacol, contains both the precursor and the enzyme. It typically includes a high-potency broccoli seed extract (providing glucoraphanin, sometimes labeled as “sulforaphane glucosinolate”) along with an added myrosinase source. A distinguishing feature is the use of “microbeadlet” technology – the ingredients are encapsulated in acid-resistant beadlets within the capsule. This design aims to protect the myrosinase from stomach acid and release it in the intestine, thereby optimizing sulforaphane conversion where pH conditions are favorable. Each capsule often corresponds to a certain glucoraphanin content (for example, 50 mg of sulforaphane glucosinolate) plus a specified amount of myrosinase (often from mustard seed extract, measured in mg of enzyme).

Bioavailability: Moderate (estimated). While specific human studies on the SM Nutrition supplement are not published, its performance should be comparable to other glucoraphanin+myrosinase combinations. One can expect on the order of 20–30% of the glucoraphanin dose to be converted and absorbed as sulforaphane in the average individual. The inclusion of myrosinase gives it a clear advantage over simple broccoli extract pills (which might only achieve ~10% or less). If the microbeadlet delivery works as intended, it could preserve more enzyme activity, potentially pushing conversion yields toward the higher end of the range (perhaps even approaching the ~30–35% seen with Avmacol under ideal conditions)【8】. However, absent direct data, a cautious estimate is that roughly one-quarter of the potential sulforaphane is realized. Users’ anecdotal reports and the manufacturer’s claims support that the product is “activated” and thus more potent than standard extracts. In essence, the SM Nutrition sulforaphane capsule attempts to mimic the effect of eating lightly steamed sprouts within a supplement. It likely succeeds to a moderate degree – significantly improving bioavailability relative to cooked broccoli or glucosinolate-only supplements, but not reaching the near-complete absorption of stabilized sulforaphane products. Factors like individual gut transit time, concomitant food, and capsule disintegration can all introduce some variability. Nonetheless, for an average user, this supplement can deliver a meaningful sulforaphane exposure (albeit less efficiently than taking an equivalent dose of actual sulforaphane).

Comparative Summary of Bioavailability

The table below summarizes the approximate sulforaphane bioavailability from each source, based on the evidence discussed. Bioavailability is given as the percentage of the ingested glucoraphanin/sulforaphane that is absorbed (as sulforaphane or its metabolites) in an average person:

GR = glucoraphanin (precursor); SF = sulforaphane.

It is evident that approaches supplying active sulforaphane (either via diet or supplement) achieve the greatest bioavailability. Lightly cooked broccoli sprouts and stabilized sulforaphane supplements both leverage active sulforaphane formation, yielding absorption in the range of roughly half to three-quarters of the available dose. On the other hand, purely glucoraphanin-based consumption – as occurs with heavily cooked sprouts or precursor-only pills – results in minimal sulforaphane uptake (often well under 10%). Supplements that include myrosinase help bridge the gap, boosting bioavailability into the tens of percent. Avmacol and similar products show that even partial in vivo conversion (20–30%) is enough to deliver health-relevant amounts of sulforaphane, though they still fall short of the efficiency of giving sulforaphane itself.

In practical terms, a user aiming to maximise sulforaphane exposure should either consume their broccoli sprouts with minimal cooking (ideally just a brief steam) or choose a supplement that provides sulforaphane in a readily available form. If using raw sprouts, techniques like chopping, blending, or adding a myrosinase-rich food (e.g. mustard powder) can improve yields, but mild heating remains the most straightforward method to enhance bioavailability【2】【6】. Among supplements, those based on stabilised sulforaphane ensure a high and reliable dose, whereas those based on glucoraphanin are more variable and inherently waste a portion of the potential sulforaphane.

References

1. Shapiro, T.A., Fahey, J.W., Wade, K.L., Stephenson, K.K., Talalay, P. (2001). Disposition of chemoprotective glucosinolates and isothiocyanates of broccoli sprouts. Cancer Epidemiology, Biomarkers & Prevention, 10(5), 501–508. PMID: 11352861.

2. Matusheski, N.V., Juvik, J.A., Jeffery, E.H. (2004). Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoli. Phytochemistry, 65(9), 1273–1281. doi: 10.1016/j.phytochem.2004.04.013.

3. Vermeulen, M., Klöpping-Ketelaars, I.W., van den Berg, R., Vaes, W.H. (2008). Bioavailability and kinetics of sulforaphane in humans after consumption of cooked versus raw broccoli. Journal of Agricultural and Food Chemistry, 56(24), 10505–10509. doi: 10.1021/jf801989e.

4. Egner, P.A., Chen, J.G., Wang, J.B., et al. (2011). Bioavailability of sulforaphane from two forms of broccoli sprout beverage: results of a short-term, cross-over clinical trial in Qidong, China. Cancer Prevention Research, 4(3), 384–395. doi: 10.1158/1940-6207.CAPR-10-0296.

5. Fahey, J.W., Holtzclaw, W.D., Wehage, S.L., et al. (2015). Sulforaphane bioavailability from glucoraphanin-rich broccoli: control by active endogenous myrosinase. PLoS ONE, 10(11), e0140963. doi: 10.1371/journal.pone.0140963.

6. Fahey, J.W., et al. (2017). Stabilized sulforaphane for clinical use: phytochemical delivery efficiency. Molecular Nutrition & Food Research, 61(4), 1600766. doi: 10.1002/mnfr.201600766.

7. Yagishita, Y., Fahey, J.W., Dinkova-Kostova, A.T., Kensler, T.W. (2019). Broccoli or sulforaphane: is it the source or dose that matters? Molecules, 24(19), 3593. doi: 10.3390/molecules24193593.

8. Panjwani, A.A., Liu, H., Fahey, J.W. (2019). 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, 11(7), 1489. doi: 10.3390/nu11071489. (Reported in: Mol. Nutr. Food Res. 2017;61:1600766)