CYP1A1 is an important enzyme involved in the detoxication of toxic substances from our bodies. However, this enzyme can also activate some toxic compounds into cancer-causing agents. That is why some CYP1A1 gene variants make people more susceptible to certain kinds of cancer. Read on to find out more about CYP1A1, its genetics, and the natural substances that can increase or decrease CYP1A1 activity.


CYP1A1 is one of the cytochrome P450 monooxygenases (CYPs). These are enzymes that help eliminate most of the drugs and toxins from the human body [1].

Read more about CYPs here.

CYP1A1 Function (Drug Metabolism)

CYP1A1 metabolizes:

  • polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene [2]. PAHs are a group of more than 100 different chemicals that are released from burning coal, oil, gasoline, trash, tobacco, wood, or charcoal-broiled meat.
  • estrogen [2, 3].

CYP1A1 is increased when environmental pollutants and chemicals bind to AhR [4].

When CYP1A1 processes PAHs, it can activate them as cancer-causing agents [2].

CYP1A1 Location

Unlike most other CYP enzymes, this one is mainly found outside of the liver, in tissues such as the lungs [5].

CYP1A1 the Good

CYP1A1 is important for the removal of toxic chemicals from our organism. Mice lacking this enzyme die within 30 days of benzo[a]pyrene treatment, whereas normal mice survive with no signs of toxicity [4].

Although this enzyme can activate cancer-causing substances, it primarily plays an important role in their detoxication [4].

It can also convert natural products found in food into anti-cancer agents [4].

Some anti-tumor drugs, such as phortress and aminoflavone, actually function by increasing CYP1A1 [4].

CYP1A1 the Bad

CYP1A1 plays a major role in activating cancer-causing chemicals, such as PAHs [5].

This enzyme is further involved in the activation of aflatoxin B1, a cancer-causing fungal toxin present in foodstuffs [4].

It also activates tobacco-related cancer-causing N-nitrosamines, such as the NNK [4].

Elevated CYP1A1 activity is associated with higher lung cancer risk (300 subjects)[5].

CYP1A1 Gene Polymorphism

  • RS4646903

The C variant (more active than the T variant) can increase susceptibility to DNA damage and cancer risk. In fact, rs4646903 was associated with leukemia, cervical, hepatocellular, lung, prostate, and head and neck cancers (meta-analysis, 268 studies, 55,963 cases, and 76,631 controls) [6, 7, 8].

On the other hand, carriers of the rs4646903 C/C showed a reduced risk of rectal cancer compared with T/T carriers (2769 subjects) [9].

This variant may increase the risk of polycystic ovary syndrome (meta-analysis, 3489 subjects)[10].

  • RS1048943

Carriers of the rs1048943 G variant have an increased risk of lung cancer (561 subjects) [7], leukemia (meta-analysis) [8] and hepatocellular carcinoma (liver cancer) (2016 subjects) [11].

  • RS2606345

Women with the rs2606345 C/C genotype (two Cs) have higher levels of this enzyme and lower levels of estradiol (1340 subjects)[12].

  • RS4646421

People carrying the rs4646421 A variant have an increased risk of hepatocellular carcinoma (2021 subjects)[11].

Increasing or Decreasing CYP1A1

These natural substances increase CYP1A1 activity:

These natural substances decrease CYP1A1 activity:

  • Berries and their component ellagic acid can reduce CYP1A1 overactivity [3].
  • Green tea extracts [18].
  • Sulforaphane found in broccoli [19].
  • St. John’s Wort [20].
  • Lycopene, a red pigment found in tomatoes, carrots, and watermelon [21].
  • Naringenin and 6′,7′-dihydroxybergamottin (from grapefruit juice) [22].
  • Galangin, found in some plants (Alpinia officinarum, Alpinia galanga, and Helichrysum aureonitens) and propolis [23].
  • Zyflamend, a widely used herbal formulation produced from the extracts of ten common herbs (rosemary, turmeric, ginger, holy basil, green tea, hu zhang, Chinese goldthread, barberry, oregano, and Baikal skullcap) [24].

These Both Increase and Decrease CYP1A:

Many foods appear to act as both inducers and inhibitors of CYP1 enzymes, based on the dose, or the differences in active compounds:

  • Curcumin at 0.1% of the diet induces this enzyme, yet a diet of 1% turmeric is inhibitory [3].
  • Black tea at 54 mL/d induced CYP1A1, yet 20 mg/kg of theaflavins was inhibitory [3].
  • Soybean intake at 100 mg/kg increased enzyme activity, yet at 1 g/kg black soybean extract and 200 mg daidzein twice daily was inhibitory [3].

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