Isothiocyanates

PhytochemicalIsothiocyanateBest with a meal

What is it

Isothiocyanates (ITCs) are sulfur-containing compounds formed when glucosinolates in cruciferous vegetables (broccoli, kale, cabbage, mustard, watercress) are hydrolyzed by the enzyme myrosinase, typically when the vegetables are chopped or chewed. The best-studied ITCs include sulforaphane, allyl isothiocyanate, and phenethyl isothiocyanate.

Evidence for 3 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Cancer chemoprevention (broad)

Good Evidence

Strong preclinical and observational evidence; cruciferous vegetable intake is associated with reduced risk of several cancers. Direct supplement RCTs are fewer.

Detoxification support (phase II enzymes)

Good Evidence

Human studies confirm ITCs upregulate phase II detoxification enzymes in tissues and blood.

H. pylori suppression

Limited Evidence

Small trials suggest sulforaphane-rich broccoli sprouts reduce H. pylori colonization; not a substitute for antibiotic eradication.

How it works

Isothiocyanates activate the Nrf2-Keap1 antioxidant pathway, inducing production of phase II detoxification enzymes (glutathione S-transferase, NAD(P)H quinone dehydrogenase 1, and others). This 'indirect antioxidant' mechanism supports cellular detoxification of carcinogens and reactive oxygen species. ITCs also modulate inflammation (NF-kB inhibition), have direct antimicrobial activity against H. pylori and other pathogens, and may have anti-cancer effects via multiple mechanisms in preclinical models. Formation depends on myrosinase activity. Cooking destroys myrosinase; raw cruciferous vegetables or supplements with intact myrosinase (or pre-formed sulforaphane) provide more ITCs. Some gut bacteria can also produce ITCs from undigested glucosinolates.

Dosage

From food: 1 to 3 servings of cruciferous vegetables daily provides meaningful ITC exposure. From supplements: standardized to 8 to 50 mg sulforaphane or specific ITCs daily; products vary widely.

When and how to take it

From food: distribute throughout day. From supplements: with food to support absorption and reduce GI irritation. Cooking briefly preserves more myrosinase than prolonged cooking.

3 commercial forms

Compare the main delivery options and what they’re best suited for.

Whole cruciferous vegetables

Best whole-food approach; broccoli, kale, cabbage, Brussels sprouts, watercress.

Provides intact glucosinolates and myrosinase when raw or briefly cooked.

Broccoli sprout extract (sulforaphane)

Most evidence-supported supplement form.

Most studied concentrated ITC; varies in stability.

Glucoraphanin + myrosinase combinations

Some products combine precursor and enzyme.

Designed to form sulforaphane during digestion.

Safety

Cruciferous vegetable consumption is universally considered safe. Concentrated ITC supplements at higher doses may cause GI upset. Allyl isothiocyanate (mustard oil) is irritating in concentrated form. Long-term safety of high-dose supplements is less established than food intake.

Who should be cautious

Hypothyroidism with iodine deficiency: very high intake of raw cruciferous vegetables may worsen; cooked vegetables are not a concern. Pregnancy: cruciferous vegetables are nutritious and safe; concentrated extracts lack data. Anticoagulants: high vitamin K in cruciferous vegetables can interact with warfarin.

Interactions

ITCs induce phase II enzymes and may alter metabolism of drugs cleared by those pathways. Theoretical interactions with thyroid medications (cruciferous goitrogen content at very high intake). Generally considered low interaction risk at food levels.

Food sources

Broccoli sprouts (high sulforaphane)

Amount
1/2 cup
%DV
—

Broccoli

Amount
1 cup cooked
%DV
—

Kale

Amount
1 cup cooked
%DV
—

Watercress (high PEITC)

Amount
1 cup
%DV
—

Mustard greens (allyl ITC)

Amount
1 cup cooked
%DV
—

Frequently asked questions

Do I get ITCs from cooked broccoli?⌄

Heavy cooking destroys myrosinase, but some ITCs still form via gut bacteria. Adding raw mustard powder to cooked broccoli can restore myrosinase activity and ITC formation.

Are ITC supplements better than vegetables?⌄

Whole vegetables provide ITCs plus fiber, vitamins, and other phytonutrients. Supplements offer concentrated ITC delivery but at the cost of these other benefits. Both can be reasonable approaches.

References

Isothiocyanates on Wikidata — Wikidata link

Isothiocyanates on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Isothiocyanates (PubMed search) — PubMed link

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.