By Sally J. Feltner, PhD, RDN
Antioxidants are supposed to protect our cells from free radicals that are dangerous highly reactive molecules seeking a missing electron. In that process, cell and DNA damage can occur contributing to disease. Antioxidants are claimed to help prevent many chronic diseases thought to be due to this damage like heart disease, cancer, macular degeneration and others. However, there is a growing body of evidence that suggests antioxidant supplements may actually promote cancer and not prevent it as they are claimed to do.
Most dietary supplements that do not exceed the Daily Values are harmless, but it is a good idea to avoid any supplement that boasts vitamin and/or mineral content over 100% of the Daily Value. Keep in mind that the studies that showed potential harm used what is known as megadoses (those greatly exceeding 100% RDA.)
Antioxidant vitamins include: beta carotene (a form of vitamin A), vitamin E and vitamin C. The mineral selenium is also considered an antioxidant.
The notion that megadoses of beta carotene might be harmful comes from studies in 1994 that resulted in smokers given megadoses of beta carotene developed 18% more cases of lung cancer than those individuals in the placebo group. A subsequent study with men smokers or those exposed to asbestos reported 28% more lung cancer cases in the beta-carotene and vitamin A groups. See my previous post HERE.
More recently, a trial in 2011 with 35,500 men found that men older than 50 years of age had a 17% higher risk for prostate cancer when given large doses of vitamin E.
Due to these disturbing studies, conclusions point to the possibility that antioxidants at least at high doses may protect cancer cells from free radicals. A recent study gave the antioxidant N-acetylcysteine (NAC) to mice genetically susceptible to melanoma. In this case, the dose was similar to those found in human consumption of antioxidants. The treated mice developed more tumors in lymph nodes that suggested a higher rate of metastasis (spread of cancer).
In addition, they added NAC or vitamin E to cultured human melanoma cells and found that antioxidants aided the cell’s ability to invade nearby tissues (a sign of increased metastasis)
In a lung cancer study using antioxidant supplements, researchers found that they turned off the activity of a known tumor suppressor gene called p53. The protein encoded by the gene monitors cells for damage to their DNA. It can trigger DNA repair; stop cell division; and even cause cancer cells to commit suicide (apoptosis).
Cancer develops in three stages: initiation, promotion and progression. It is thought that antioxidant supplements do not initiate cancer cells but speed up the progression to malignancy of undiagnosed or already present cancer cells.
To give us an idea of the labels on some selected products at a popular health food store:
Beta Carotene is a form of vitamin A.
1 capsule provides 15 mg – 500% Daily Value.
Vitamin C 1000 mg.
! caplet provides 6667% Daily Value
Health Claim on Label: A protective antioxidant that provides immune support.
Vitamin E 1000 IU
1 capsule provides 3333% of Daily Value
Health Claim on Label: Helps support a healthy cardiovascular system
Some cancer researchers believe that people who are at a higher risk for lung cancer or melanoma or have any form of cancer should avoid antioxidant supplements. However, there is widespread evidence that eating fruits and vegetables can help lower the risk of heart disease and certain cancers. Do not fall for the hype of supplement sellers and manufacturers who ignore the science. The concept of the free radical theory of disease is a complex issue and should not be left to the interpretations of those who only take in the profits of possibly harmful products.