New Animal Research Reveals Risks of “Healthy” Supplements Like Beta-Carotene
Antioxidants are believed to help keep cells healthy. That’s why millions of people take vitamin E, beta-carotene, and other antioxidant supplements every year. However, recent scientific studies show that these substances can be unexpectedly harmful in certain serious conditions, especially cancer.
A new study on mice found that antioxidants can help cancer cells spread to different parts of the body. In particular, melanoma — one of the most aggressive and deadly forms of skin cancer — may metastasize faster under the influence of antioxidants. The spread of cancer indicates progression to a more severe and potentially fatal stage.
Troubling Findings from Previous Human Studies
Earlier research also raised concerns about the link between antioxidant supplements and cancer risk.
In a large clinical trial in 1994, men who smoked and took high doses of beta-carotene daily had an 18% higher risk of lung cancer. The trial was stopped early in 1996 after high doses of beta-carotene and retinol (a form of vitamin A) were found to increase cancer risk.
Another form of vitamin A increased lung cancer risk by 28% in smokers and asbestos-exposed workers.
In a 2011 study involving over 35,500 men over 50, high doses of vitamin E were linked to a 17% higher risk of prostate cancer.
These findings surprised researchers, as antioxidants are generally thought to reduce cancer risk by neutralizing free radicals that damage cells.
What’s the Problem?
Modern science suggests the main issue is the high levels of antioxidants. In these conditions, they protect not only healthy cells but also cancer cells. Notre Dame biologist Zachary Schafer notes that mounting evidence shows antioxidants can help cancer cells just as they help normal cells.
Studies indicate that antioxidants accelerate the growth of not only melanoma but also lung cancer.
New Research on Melanoma
Published in Science Translational Medicine, a study by researchers at the Sahlgrenska Cancer Center in Gothenburg, Sweden, focused on melanoma because this cancer is particularly sensitive to free radicals.
Genetically predisposed mice received the antioxidant N-acetylcysteine (NAC). The doses matched those typically consumed by humans through supplements. Results showed:
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Skin tumor numbers did not increase,
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but the number of metastatic tumors in lymph nodes doubled.
Experiments on human melanoma cells produced similar results: NAC and vitamin E enhanced the cells’ ability to move and invade surrounding tissues.
Glutathione and Metastasis
Mice receiving antioxidants showed higher levels of the endogenous antioxidant glutathione in metastatic tumor cells. After neutralizing free radicals, glutathione converts to glutathione disulfide, and an increased ratio makes cells more resistant to oxidative stress. This allows cancer cells to survive and spread more effectively. Glutathione also boosts the activity of RhoA, a protein crucial for cell migration.
Previous studies showed that antioxidants can suppress p53, a tumor-suppressor gene, whose inactivation accelerates metastasis.
Clinical Implications
These molecular mechanisms help explain why antioxidants had negative outcomes in large human trials. They do not directly cause cancer but may accelerate the progression of pre-existing, undiagnosed tumors.
Medical Advice
At this stage, consulting a doctor is especially important. Further studies are needed to fully understand antioxidants’ effects on human cancer cells. Martin Bergö, one of the study authors, advises that people at high risk for lung cancer or melanoma, or those already diagnosed, should avoid antioxidant supplements:
“There is no evidence of benefit, but there is strong evidence of potential harm.”
A Promising Perspective
At the same time, these findings offer hope for new treatment strategies. If cancer cells are particularly vulnerable to free radical damage, it may be possible in the future to develop targeted drugs that:
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Block antioxidant production within cancer cells, or
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Increase free radical levels inside malignant cells,
thereby exploiting newly identified vulnerabilities in cancer biology.