It costs pennies, but it supports the fight against cancer. Scientists: This is a surprising discovery.

• Zeaxanthin, known primarily for protecting eyesight, has also been shown to enhance the activity of immune cells in the fight against cancer.
• Studies have shown that it stabilizes CD8+ T cell receptors, which increases their ability to destroy cancer cells.
• In experiments on mice, zeaxanthin supplementation slowed the growth of tumors and enhanced the effects of anticancer immunotherapies.
• Zeaxanthin is cheap, safe, and available in diet or supplements, but further human clinical trials are needed.

Zeaxanthin is a natural carotenoid compound found in the retina and is essential for health. Its powerful antioxidant properties protect the cells of the retina's macula from damage caused by free radicals and UV radiation. The human body cannot produce zeaxanthin on its own , so it must be supplied externally, primarily through a diet rich in fruits and vegetables—or supplements.

Now, scientists from the University of Chicago (USA) have discovered that zeaxanthin can also increase the activity of immune cells in the fight against cancer .

The authors highlight the potential of zeaxanthin as a widely available supplement that may improve the effectiveness of anticancer immunotherapies.

"It's a surprising discovery that zeaxanthin, already known for its role in eye health, has a completely new function in strengthening anti-cancer immunity. Our study shows that a simple dietary nutrient can complement and enhance the effectiveness of advanced cancer treatments, such as immunotherapy," said Dr. Jing Chen, lead author, as quoted in the press release.

By examining a large library of blood nutrients, Chen's team identified zeaxanthin as a compound that directly enhances the activity of CD8+ T cells, a key type of immune cell that kills cancer cells. These cells use a molecular structure called the T cell receptor (TCR) to recognize and destroy abnormal cells.

Scientists have found that zeaxanthin stabilizes and enhances TCR complex formation on CD8+ T cells after interaction with cancer cells. This, in turn, triggers stronger intracellular signaling that enhances T cell activation, cytokine production, and tumor-killing capacity.

In mouse models, dietary supplementation with zeaxanthin slowed tumor growth. Importantly, when combined with immune checkpoint inhibitors—a type of immunotherapy that has revolutionized cancer treatment in recent years—zeaxanthin significantly enhanced its antitumor effects compared to immunotherapy alone.

To expand on the study, the researchers tested human T cells genetically modified to recognize specific tumor antigens and found that zeaxanthin treatment improved the cells' ability to destroy melanoma, multiple myeloma, and glioblastoma multiforme cells in laboratory experiments.

Zeaxanthin is sold over-the-counter as a dietary supplement intended to improve eye health. It occurs naturally in vegetables like bell peppers (especially yellow, orange, and red), spinach, and kale (eating these foods with fat facilitates zeaxanthin absorption). It is inexpensive, widely available, well-tolerated, and, most importantly, its safety profile is known—meaning it can be safely tested as an adjunct to cancer therapies.

The study also highlights the importance of a balanced diet. In previous studies, Chen's group found that trans-vaccenic acid (TVA), a fatty acid derived from dairy and meat and produced by bacteria in the digestive tract of cattle, also increases T cell activity—but through a different mechanism. Together, the results suggest that nutrients from both plant and animal sources may provide complementary benefits for immune health.

Although the results are promising, the researchers emphasize that the work is still in its early stages. Most findings come from laboratory experiments and animal studies. Therefore, clinical trials will be necessary to determine whether zeaxanthin supplements can improve outcomes in cancer patients.