Indole-3-carbinol (I3C) is the cruciferous compound that is one of the most important ligands of the aryl hydrocarbon receptor (AhR) — it is formed from the glucobrassicin in the cruciferous vegetables (particularly the broccoli, the cabbage, the Brussels sprouts, the kale, and the cauliflower) when they are chewed or digested, and it is one of the most important and most evidence-based compounds for the modulation of the oestrogen metabolism, the regulation of the immune function, and the prevention of the hormone-related cancers. Indole-3-carbinol activates the AhR primarily through its direct binding to the AhR protein — when the I3C binds to the AhR, the AhR translocates to the nucleus, dimerises with the ARNT (aryl hydrocarbon receptor nuclear translocator), and induces the transcription of the AhR target genes (including the CYP1A1, the CYP1A2, the GST, and the UGT). The AhR activation by the I3C is the primary mechanism of its effects on the oestrogen metabolism (it induces the CYP1A2 and the 2-hydroxylation of the oestradiol, thereby shifting the oestrogen metabolism toward the less carcinogenic 2-hydroxyestrone and away from the more carcinogenic 16alpha-hydroxyestrone), on the immune function (it regulates the differentiation and the activity of the T helper cells, the regulatory T cells, and the dendritic cells through the AhR-dependent signalling), and on the cancer prevention (it induces the apoptosis and inhibits the proliferation of the cancer cells through the AhR-dependent and the AhR-independent pathways). Without adequate indole-3-carbinol and AhR activation, the oestrogen metabolism is dysregulated, the immune function is impaired, and the cancer initiation is promoted — the hallmark of the indole-3-carbinol deficiency and of the AhR insufficiency states that are associated with the oestrogen dominance, the autoimmunity, and the increased risk of the breast cancer, the cervical cancer, and the prostate cancer.
Indole-3-Carbinol and the Oestrogen Metabolism
Indole-3-carbinol supports the favourable oestrogen metabolism primarily through its activation of the CYP1A2 and the induction of the 2-hydroxylation pathway — the CYP1A2 is the enzyme that converts the oestradiol to the 2-hydroxyestrone, which is a weak and non-carcinogenic oestrogen metabolite that does not promote the breast cancer or the cervical cancer growth. When the I3C induces the CYP1A2, it shifts the oestrogen metabolism away from the 16alpha-hydroxylation pathway (which produces the 16alpha-hydroxyestrone, a strong and carcinogenic oestrogen metabolite that promotes the breast cancer and the cervical cancer growth) and toward the 2-hydroxylation pathway (which produces the 2-hydroxyestrone, a weak and anticarcinogenic oestrogen metabolite). This shift in the oestrogen metabolism is the primary mechanism by which the I3C reduces the risk of the hormone-related cancers (breast cancer, cervical cancer, ovarian cancer, prostate cancer) and it is the reason why the I3C-rich cruciferous vegetables have been associated with the reduced risk of these cancers in multiple large observational studies. The I3C also has a secondary anti-cancer effect through its condensation product, the 3,3′-diindolylmethane (DIM), which is formed in the stomach under the acidic conditions — the DIM is a more potent AhR ligand than the I3C itself, and it is therefore responsible for a significant portion of the AhR-mediated anticancer effects of the cruciferous vegetables.
The clinical importance of the indole-3-carbinol for the cancer prevention is underscored by the observation that the I3C supplementation reduces the oestrogen metabolites and improves the hormone metabolism in women with the oestrogen dominance and with the increased risk of the breast cancer. A study in 30 women with the oestrogen dominance (elevated 16alpha-hydroxyestrone/2-hydroxyestrone ratio) found that the I3C supplementation at 400mg daily for 3 months significantly shifted the oestrogen metabolism toward the 2-hydroxylation pathway (increasing the 2-hydroxyestrone by 40-50% and decreasing the 16alpha-hydroxyestrone by 30-40%), and improved the 2/16alpha ratio to the favourable range — demonstrating the potent and clinically meaningful oestrogen-modulating effect of the I3C in women with the oestrogen dominance and with the increased risk of the hormone-related cancers.
Practical Application
For general indole-3-carbinol supplementation for the AhR activation and for the oestrogen metabolism support, the evidence-based approach is to supplement with 200-400mg of I3C daily (as the pure indole-3-carbinol powder or capsule, or as the standardised broccoli extract or cruciferous vegetable extract that is standardised to contain 10-20% I3C). The I3C should be taken with the DIM (diindolylmethane) (which is the primary condensation product of the I3C and which is a more potent AhR ligand and a more effective oestrogen modulator than the I3C itself — the combination of the I3C and the DIM is one of the most effective and most evidence-based approaches for the oestrogen metabolism support and for the prevention of the hormone-related cancers). The I3C is generally well-tolerated with no significant adverse effects at the doses that are used for the AhR activation (up to 800mg daily), though the very high doses may cause the mild gastrointestinal discomfort or the skin rash in some individuals. For comprehensive AhR activation and oestrogen metabolism support, indole-3-carbinol pairs well with the DIM (which is the active metabolite that works synergistically with the I3C for the AhR activation and for the oestrogen metabolism modulation — the combination of the I3C and the DIM is one of the most effective approaches for the oestrogen metabolism support and for the prevention of the hormone-related cancers), with the calcium-d-glucarate (which is an inhibitor of the beta-glucuronidase and which works synergistically with the I3C for the oestrogen detoxification and for the prevention of the oestrogen dominance — the combination of the I3C and the calcium-d-glucarate is one of the most effective combinations for the comprehensive hormonal balance and for the prevention of the breast cancer and of the prostate cancer), with the sulforaphane (which is another NRF2 activator that works synergistically with the I3C for the phase II detoxification and for the comprehensive cancer prevention — the combination of the I3C and the sulforaphane is one of the most effective combinations for the prevention of the cancer and for the protection from the environmental toxins), and with the ellagic acid (which is another NRF2 activator that works synergistically with the I3C for the phase II enzyme induction and for the maximum detoxification capacity — the combination of the I3C and the ellagic acid is one of the most effective combinations for the comprehensive liver detoxification support and for the prevention of the cancer initiation).
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