PSK (Krestin)

What It Is

PSK (Polysaccharide Krestin), also known simply as Krestin, is a protein-bound polysaccharide derived from the Coriolus versicolor mushroom (also called Trametes versicolor or “Turkey Tail”). It is a biologically active compound composed primarily of β-glucans linked with peptides. PSK has been widely used in Japan and other Asian countries as an immunotherapeutic agent, particularly as an adjuvant treatment for cancer. It is classified as a biological response modifier (BRM), meaning it modulates the body’s immune system to enhance its ability to fight disease.

How It Works

PSK works through immune modulation, meaning it helps stimulate or regulate the body’s natural immune defenses. The key mechanisms include:

1. Activation of Immune Cells: PSK activates various immune cells such as macrophages, dendritic cells, natural killer (NK) cells, and T lymphocytes. This activation enhances the body’s ability to identify and destroy abnormal or cancerous cells.
2. Cytokine Regulation: It promotes the production of cytokines (e.g., interleukins, interferons, and tumor necrosis factors), which are signaling molecules that coordinate the immune response and help orchestrate anti-tumor activity.
3. Enhancement of Antitumor Immunity: PSK is believed to increase the presentation of tumor antigens to the immune system, improving immune surveillance and the targeting of tumor cells.
4. Reduction of Immunosuppression from Chemotherapy: Many conventional cancer treatments (like chemotherapy and radiation) suppress immune function. PSK helps counteract immunosuppression, allowing the body to recover immune competency during or after therapy.
5. Antioxidant and Anti-inflammatory Effects: Beyond immune modulation, PSK exhibits antioxidant properties that protect cells from oxidative damage and may help regulate inflammatory responses that contribute to disease progression.

Why It’s Important

PSK’s importance lies in its role as a complementary cancer therapy and immune-enhancing agent. Key points include:

• Clinical Use in Oncology: PSK has been approved for clinical use in Japan since the 1970s as an adjunct therapy for cancers such as gastric, colorectal, lung, breast, and esophageal cancers. It is used alongside chemotherapy to improve survival rates and quality of life.
• Evidence of Improved Outcomes: Studies (mainly from Japan and China) have reported that patients receiving PSK in combination with conventional cancer therapies often experience longer survival times and lower recurrence rates compared to those receiving standard therapy alone.
• Support for Immune Health: Beyond oncology, PSK’s immune-boosting effects have led to its investigation for viral infections, chronic fatigue, and general immune support, though evidence outside cancer remains limited.
• Natural Source: Derived from a medicinal mushroom with a long history of use in traditional Asian medicine, PSK represents a bridge between modern pharmacology and natural immunotherapy.

Considerations

While PSK shows promise and has clinical backing in certain countries, there are important considerations to keep in mind:

1. Regulatory Differences: PSK is an approved prescription drug in Japan, but in most Western countries (including the U.S.), it is classified as a dietary supplement or investigational substance, not an approved pharmaceutical agent.
2. Scientific Debate and Evidence Quality: Although numerous studies (especially in Asia) support PSK’s efficacy, methodological differences and variations in study quality have made it difficult for regulatory bodies like the FDA or EMA to fully endorse it as a standard therapy.
3. Dosage and Administration: In clinical settings, PSK is typically administered orally in standardized doses as part of a structured cancer treatment plan. Over-the-counter versions may differ in purity and potency.
4. Potential Side Effects: PSK is generally well tolerated, but some individuals may experience digestive upset, darkened stool, nausea, or allergic reactions. Because it modulates immune function, caution is advised in people with autoimmune diseases or those on immunosuppressive medications.
5. Interactions with Conventional Therapies: Patients should consult healthcare providers before combining PSK with other treatments, as immune-boosting agents could theoretically interfere with immunosuppressive or cytotoxic drugs.
6. Product Quality Variability: Since PSK supplements sold outside Japan are not strictly regulated, product quality, extraction methods, and concentration can vary widely, affecting safety and efficacy.