Antioxidants are known to protect against cancer. However, a recent study found that antioxidants actually helped cancer cells to grow, negating the previous belief that they aid in cancer prevention and reinforcing what other studies have found -- that antioxidants are harmful for people with cancer.
Researchers investigated how an antioxidant supplement called N-acetylcysteine (NAC) would affect melanoma in mice. They gave the mice NAC for 80 days and found that the number of tumors doubled at the end the experiment. The tumors also spread to the lymph nodes. On the other hand, the tumors of mice that were not given NAC did not increase, according to Live Science.
Additionally, the researchers investigated how human melanoma cells grown in the lab would respond to NAC and another popular antioxidant, vitamin E. After exposing the melanoma cells to the antioxidants, the researchers found that the cancer cells showed a greater ability to spread to other tissues compared to those that were not exposed to the antioxidants.
"It is not far-fetched to propose that antioxidants could increase [the spread of cancer] in melanoma patients," study author Martin Bergo from the University of Gothenburg in Sweden told Live Science. "Therefore, we would recommend people who have been diagnosed with malignant melanoma to avoid antioxidant supplements."
The study's results are similar to those from a 2014 study from the same authors, which showed that antioxidants accelerated the growth of lung cancer cells in mice. A separate 2013 study from different authors found that vitamin E increased the risk of developing prostate cancer in healthy men by 17 percent.
Does this mean that people should avoid antioxidants altogether? Ekaterina Dadachova, radiology professor at Albert Einstein College of Medicine who was not involved in the study, told Live Science that supplements have much higher levels of antioxidants than natural foods.
"One would have to eat several pounds of vitamin-E-containing food in order to reach the level that would be in one supplement tablet," she said, adding that it is safe to eat natural food that contains antioxidants.
Dr. Vadim Gushchin at the Mercy Medical Center, who was also not involved in the study, said more studies are needed to establish the link between antioxidant supplements and the increased growth of cancer cells.
The study was published in the Oct. 7 issue in the journal Science Translational Medicine.