The Anti-Tumor Effect of Quercetin and the Chinese Herbs and Foods That Contain It

Quercetin, a natural flavonoid compound, has drawn much attention in anti-tumor research in recent years. Some in vitro and animal experiments show that quercetin has broad-spectrum, multi-target anti-tumor effects, inhibiting the proliferation of many tumor cells including esophageal, gastric, liver, pancreatic, colorectal, colon, lung, breast, cervical, prostate, ovarian, bladder cancer, melanoma, and retinoblastoma cells.

Quercetin exerts its anti-tumor effect by modulating cell signaling pathways, inhibiting tumor cell proliferation, inducing apoptosis, suppressing angiogenesis, and synergizing with chemotherapy drugs. Some experimental results show that quercetin exerts a chemopreventive effect on tumors by inhibiting cell proliferation and through complex actions on angiogenesis-related signaling pathways.

Dietary quercetin can effectively reduce the carcinogenic action of chemical carcinogens, especially against colon and lung cancer. Quercetin aglycone can interact with certain aryl hydrocarbon receptors, which play a role in cancers induced by specific chemical carcinogens. Another study showed that giving healthy men blackcurrant drinks supplemented with quercetin for 2 weeks significantly lowered the transcriptional level of the TIMP-1 gene and plasma protein levels in peripheral blood.

The anti-tumor mechanism of quercetin is complex, and research on it is still ongoing. The following are the main mechanisms and related research progress:

1. Quercetin can induce tumor cell apoptosis: by up-regulating pro-apoptotic proteins (such as Bax, Caspase-3) and down-regulating anti-apoptotic proteins (such as Bcl-2), quercetin triggers collapse of the mitochondrial membrane potential and activates apoptosis. It can also promote programmed cell death by activating the Fas/FasL signaling pathway.

2. Quercetin can inhibit tumor cell proliferation: it can arrest tumor cells in G1 or G2/M phase, inhibiting DNA replication and mitosis. Quercetin can also limit tumor growth by inhibiting telomerase activity. For example, in breast and colon cancer cells, quercetin down-regulates Cyclin D1 and CDK4/6 expression to inhibit cell-cycle progression.

3. Quercetin can inhibit tumor angiogenesis: by down-regulating VEGF and matrix metalloproteinases (MMPs), it suppresses new vessel formation and cuts off the tumor's nutrient supply.

4. Quercetin can scavenge free radicals, acting as an antioxidant and anti-inflammatory, reducing oxidative stress damage to DNA and thus lowering the risk of gene mutation.

5. Quercetin can enhance chemosensitivity, reduce radiation damage to normal tissues, and increase tumor-cell radiosensitivity. Clinical trials show that by inhibiting multidrug resistance proteins (such as P-gp), quercetin enhances the efficacy of chemotherapy drugs (such as cisplatin and doxorubicin), lowers chemotherapy-induced oral mucositis, improves quality of life, and prolongs survival. Animal experiments show that quercetin combined with cisplatin significantly shrinks liver tumors in mice. Quercetin can also reduce tumor metastasis by inhibiting the STAT3 pathway. Some studies show quercetin may affect certain drug-metabolizing enzymes (such as CYP3A4), so combining it with chemotherapy requires caution.

Quercetin is found in many Chinese herbs. Common herbs containing it include Huai mi (Sophorae Flos Immaturus), Huai hua (Sophorae Flos), Yinxingye (Ginkgo biloba leaf), Huangqin (Scutellaria), Jinyinhua (Lonicera), Gegen (Pueraria), Juhua (Chrysanthemum), Shanzha (Hawthorn), Cebaiye (Biota leaf), Yinchen (Artemisia), Qiaomai (Buckwheat), and Luobuma ye (Apocynum leaf). Most belong to the TCM categories of heat-clearing, detoxifying, blood-cooling, and swelling-reducing herbs, traditionally used for sores, carbuncles, and ulcers.

Foods rich in quercetin include onions, cabbage, apples, blueberries, cranberries, oranges, lemons, tomatoes, spinach, almonds, walnuts, and red wine—most of which are also natural cancer-preventive foods.

Besides natural herbs and vegetables, modern pharmaceutical companies also produce convenient oral quercetin preparations. The following are three common ones.

Compound Quercetin Capsules: Besides quercetin, this preparation adds extracts of Fengweicao (Pteris multifida), Banbianlian (Lobelia), and Cheqiancao (Plantago), plus bromelain and vitamins B6, C, and B12. Through scientific proportioning it enhances absorption and synergy; it is mainly used for respiratory protection (such as prevention of Mycoplasma pneumoniae infection) and lung health, and may be used as adjuvant therapy for lung and colon cancer.

Quercetin Capsules: This preparation uses quercetin as the main ingredient, supplemented with bromelain and hesperidin, targeting cough with abundant phlegm, people exposed to dust at work, or those needing lung care; it combines anti-inflammatory, antioxidant, and respiratory-immunity-enhancing effects.

Quercetin Sustained-Release Tablets: Ordinary quercetin has a short half-life (2-4 hours) requiring frequent dosing; sustained-release tablets achieve long-acting release (up to 12 hours), requiring only 1-2 doses daily and reducing blood-concentration fluctuations. This preparation is suitable for patients with hypertension, coronary heart disease, or those needing long-term anti-tumor treatment.

Although quercetin has multi-target anti-tumor potential, most research on it is still at phase I/II clinical stage; the stability of its efficacy still needs further exploration, and it cannot yet replace standard radiotherapy and chemotherapy. Large-dose quercetin also has side effects; long-term high-dose use may cause kidney damage. Patients taking quercetin should have regular liver and kidney function checks.