French scientists have shown that taking antioxidant supplements, which include vitamins C and E and beta carotene, may increase a woman's risk of skin cancer by 68 percent.
The risk of melanoma, the most serious form of skin cancer, was four times greater for women taking the antioxidant supplements.
A study released in the Journal of Nutrition on Monday examined the relationship between antioxidant use and skin cancer risk.
The researchers looked at about 13,000 French adults, ages 35 to 60, half of whom took an oral daily capsule of antioxidant that contained vitamins C, E, beta carotene and selenium. The other half took a placebo.
The researchers then recorded how many got skin cancer over an average period of 7½ years.
What they found was that 51 of the women taking the antioxidants developed skin cancer, compared to only 30 percent of those taking the placebo.
The findings were a surprise to many who believed that antioxidants actually protect against sun damage that leads to skin cancer. And some researchers say more evidence is needed before a definitive verdict can be delivered on the supplements.
In theory, exposure to ultraviolet light, usually the sun, increases the amount of "free radicals" in the skin — the microscopic "vandals" indicted in skin cancer.
The authors state that, "Excessive exposure to sunlight or other sources of UV light can overwhelm the skin's antioxidant power."
It is for this reason that antioxidant pills have been recommended for the prevention of sunburns and for their protective properties.
Previous studies on animals have shown that when antioxidants are given prior to exposure to ultraviolet light there is a protective effect against skin cancer.
This study, the researchers say, was different because the "antioxidants are given only after many years of exposure to sunlight." They conclude that at this stage in life — ages 35 to 60 — it may be too late to prevent genetic damage, hence the skin cancer.
"This study suggests that antioxidants may not be as protective for skin cancer as many believe," said Murad Alam, professor of dermatology at Northwestern University in Chicago.
Roger Clemens, doctor of pharmacy at University of Southern California, agrees, but he thinks similar information regarding lack of beneficial antioxidant effects have been found before.
"These findings are not surprising," Clemens said. "Prior studies indicated that vitamins C, E and beta carotene were not cardioprotective [heart protective] for women."
And Jeffrey Blumberg, director of the antioxidants research laboratory at Tufts University in Boston, points to a study that demonstrated that high-dose beta carotene can lead to lung cancer in individuals who smoke.
Other researchers note that the findings of the study could be called into question based on the fact that the research was initially designed to find something else entirely — the effects of antioxidants on reducing (rather than increasing) the incidence of cancer and heart disease.
"It is difficult to attribute much significance to this study as it was not designed to answer the question being asked," Blumberg said.