Also, critics of the study feel that the number of skin cancers reported — 157 in total — was too small to draw the conclusion that antioxidants are associated with higher skin cancer risk in women.
Scientifically speaking, it is unlikely that the difference was due to chance alone. Some, however, were still wary of the study's results.
"The small number of skin cancers is concerning," said Alam.
"Different results might have been found if they gave the antioxidants to younger people and followed them for a longer period of time," said Mary Kavanagh, a nutritionist at Case Western University in Cleveland. She adds that many people do not develop skin cancer until they're in their 70s.
The other mystery is why the increased risk was seen in women, but not in their male counterparts.
The researchers found no difference in skin cancer rates among the men who were taking the antioxidant or placebo. They speculate that this may be, "attributed in part to differences in nutrient metabolism." Women, the researchers say, tend to have, "higher concentrations of antioxidants in the skin," thought to be related to a higher dietary intake when compared to men.
"Women have thinner skin than males, thus, ultraviolet damage could reach the skin more readily," said Jana Klauer, a New York-based physician who specializes in nutrition and metabolism. "There are estrogen receptors in skin, which may play a role as well."
Consumers continue to purchase over-the-counter antioxidants at a rapid rate despite studies, including this one, that indicate they offer no benefit and may even be harmful. Thus, the underlying question remains as to what people can do to protect themselves from skin cancer.
"The best protection against skin cancer is achieved by avoiding the sun, wearing protective clothing and using a good sunscreen," Klauer said. "This is especially important for anyone who is fair-skinned or who had a serious sunburn as a child. … Simply taking an antioxidant vitamin is folly."
Clemens thinks that the key is in eating your antioxidants in the form of fruits and vegetables rather than in pill form.
"These kinds of studies suggest that single nutrients versus those found in a food matrix may not be as effective in reducing risk for specific health conditions," he said.