Indole-3-Carbinol — I3C (Glucosinolate Product · Oestrogen Metabolism · Chemopreventive)

Compound	Indole-3-Carbinol (I3C)
Chemical class	Glucosinolate Hydrolysis Product — Indole Alcohol
CAS	700-06-1
Primary source	Hydrolysis of glucobrassicin in Brassica oleracea (broccoli, cabbage, Brussels sprouts)
Key applications	Oestrogen metabolism modulation, chemopreventive, hormonal balance, antiviral
Claim strength	Moderate
Typical form	I3C isolate; broccoli extract (I3C as glucobrassicin hydrolysis product)
Buy from Herbuno	Broccoli Extract Powder - Brassica oleracea →

Name origin: Indole (bicyclic aromatic ring from tryptophan biosynthetic pathway) + 3-carbinol (carbinol = primary alcohol, at position 3 of the indole ring). I3C is the direct hydrolysis product of glucobrassicin (via myrosinase) before further acid-catalysed condensation to DIM and other oligomers. Traditional use: No individual traditional use of I3C — it was identified as a specific compound in cruciferous vegetables in the 1970s. Cabbage juice’s traditional anti-ulcer properties (Garnett Cheney’s 1950s work) may partially involve I3C alongside other Brassica phytochemicals. Research trajectory: I3C has been investigated in human clinical trials for oestrogen metabolism modulation (shifting oestradiol hydroxylation toward the less active 2-OHE1 pathway), cervical dysplasia regression, breast cancer chemoprevention, and antiviral activity (HPV-associated respiratory papillomatosis). I3C is less stable than its condensation product DIM — it is rapidly converted to DIM and other condensation products in the acid gastric environment, making DIM the more pharmacologically consistent supplement form for most applications. Commercial source: Broccoli Extract Powder from Herbuno delivers I3C precursors (glucobrassicin). See sourcing options below.

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Evidence for I3C Applications

Oestrogen metabolism modulation: Human studies with I3C (200–400 mg/day) consistently show increased urinary 2-OHE1/16α-OHE1 ratio (the “oestrogen metabolite ratio”) over 4–12 weeks. A higher 2-OHE1/16α-OHE1 ratio is associated with reduced breast cancer risk in epidemiological studies. I3C also induces CYP1A1 and CYP1A2, increasing oestradiol 2-hydroxylation. Claim strength: Moderate (human biomarker studies).

Cervical dysplasia regression: The Bell et al. 2000 RCT (n=30 women with CIN 2/3) showed complete regression in 50% of women receiving I3C (200–400 mg/day) for 12 weeks versus 0% placebo. This is a clinically significant finding for I3C in HPV-associated cervical pre-cancer. A larger confirmatory trial showed mixed results. Claim strength: Moderate (one positive RCT; one less conclusive follow-up).

Antiviral — respiratory papillomatosis: I3C has been investigated for HPV-associated recurrent respiratory papillomatosis (RRP) — a chronic respiratory condition caused by HPV 6/11. Human case series and small trials show I3C (8 mg/kg/day paediatric) reduces papilloma recurrence rate in some RRP patients. The mechanism involves I3C’s modulation of HPV E6 and E7 protein expression. Claim strength: Moderate (case series and small trials).

Anti-androgenic: I3C and DIM inhibit androgen receptor transcriptional activity (competitive AR binding, ubiquitination-mediated AR degradation). Relevant for PCOS, prostate health, and male hormonal balance. Claim strength: Moderate.

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Dosage & Formulator Specification

Human clinical dose: 200–400 mg/day I3C for hormonal and chemopreventive applications. I3C is unstable — it converts to DIM and other condensation products in acidic gastric conditions. Bioavailability of intact I3C is limited; most systemic effect is mediated by DIM and other acid-condensation products formed in the stomach. For consistent delivery of the endpoint active (DIM), DIM supplements are preferred over I3C. I3C is appropriate when the full spectrum of I3C acid-condensation products (DIM + linear trimer + CTet + other oligomers) is desired rather than DIM alone.

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Frequently Asked Questions — Indole-3-Carbinol

Should I take I3C or DIM for hormonal balance?
DIM (diindolylmethane) is the primary pharmacologically active metabolite formed from I3C in the stomach. At equivalent doses, DIM provides more predictable and consistent systemic exposure than I3C because it bypasses the variable acid-condensation step. DIM is the preferred form for targeted hormonal balance and oestrogen metabolism applications. I3C may be appropriate when the broader spectrum of acid-condensation products (including DIM, CTet, and linear trimer) is desired, as some of these co-products have distinct pharmacological activities not reproduced by DIM alone.

Is I3C safe for oestrogen-sensitive conditions?
I3C’s oestrogen metabolism modulation (increasing 2-OHE1 relative to 16α-OHE1) is generally considered protective against hormone-sensitive cancers in epidemiological data. However, at high doses I3C can activate ERα in some contexts, which is undesirable in ER-positive breast cancer. Women with hormone-sensitive cancers or on hormone therapy should consult their oncologist before I3C supplementation. At dietary cruciferous vegetable consumption levels (equivalent to 1–3 cups/day broccoli), I3C exposure is considered safe for the general population.

What is CTet and why does it matter?
5,6,11,12,17,18-hexahydrocyclonona[1,2-b:4,5-b’:7,8-b“]triindole (CTet) is the cyclic trimer formed from three I3C molecules in the gastric acid environment. CTet has potent aryl hydrocarbon receptor (AhR) agonist activity — stimulating CYP1A1 gene expression and influencing xenobiotic metabolism. Some I3C pharmacological effects (CYP1A induction) may be mediated by CTet rather than I3C or DIM directly. This is why the complete I3C acid-condensation product mixture has a different pharmacological profile from isolated DIM.

Can I3C be used topically for skin and cosmetic applications?
I3C has been investigated for topical anti-ageing applications — it inhibits VEGF-mediated angiogenesis and reduces UV-induced skin damage in cell models. However, I3C’s chemical instability (condensation to DIM and other products) makes topical formulation challenging. DIM is more chemically stable and is preferred for topical applications targeting hormonal balance in skin sebum regulation (for acne). For topical antioxidant applications, sulforaphane (from broccoli extract) is more established than I3C.

Related compounds: Glucobrassicin, Diindolylmethane, Sulforaphane, Glucoraphanin

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Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.

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