A common nutrient found in leafy greens and corn may do more than protect eyesight. 

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New research shows that zeaxanthin, a plant-derived carotenoid, can strengthen the body’s cancer-fighting immune cells and make immunotherapy more effective.

The study, recently published in the journal Cell Reports Medicine, found that zeaxanthin enhanced the ability of CD8+ T cells — immune cells that kill tumors — to attack cancer. 

When given orally to mice, the nutrient slowed the growth of melanoma and colon tumors. That effect disappeared when CD8+ T cells were removed.

“We were surprised to find that zeaxanthin, already known for its role in eye health, has a completely new function in boosting anti-tumor immunity,” said senior author Dr. Jing Chen, a professor of medicine at the University of Chicago. 

“Our study shows that a simple dietary nutrient could complement and strengthen advanced cancer treatments like immunotherapy,” he added in a news release.

The researchers discovered that zeaxanthin helps stabilize the T-cell receptor (TCR) complex on CD8+ T cells. This makes the receptor work better and strengthens signals inside the cell. 

As a result, the T cells produce more cytokines, which help them attack cancer more effectively.

In additional lab tests, zeaxanthin improved the tumor-killing ability of engineered human T cells against melanoma, multiple myeloma and glioblastoma cells. And pairing zeaxanthin with immunotherapy in mice further slowed tumor growth compared with immunotherapy alone, researchers said.

Zeaxanthin is widely available as an over-the-counter supplement for eye health. The researchers stressed, however, that clinical trials are needed to test whether these benefits are the same for cancer patients.

Results of tests in animals are often different in humans.