Vitamin A supplements could reduce the risk of developing the deadly skin cancer melanoma, according to a new study.
The results show that people taking vitamin A were 60 percent less likely to develop melanoma over the six-year study. People who had taken the vitamin, but weren't currently taking it, did not gain any protective effect.
The reduced risk was more pronounced in women than men.
"This is promising evidence that in addition to sun protection, there's another option that can help prevent melanoma," said Dr. Mary Gail Mercurio, a dermatologist at the University of Rochester Medical Center, who was not involved with the study.
Vitamin A is found in foods such as sweet potato, carrots, spinach, milk, eggs and liver. The vitamin plays an important role in vision, bone health, immune function and reproduction, but high doses of it can be toxic.
The study appears today (March 1) in the Journal of Investigative Dermatology.
Genetics could increase melanoma risk
Melanoma is the sixth leading cause of cancer in the U.S., according to the American Cancer Society. About 76,000 cases of melanomas will be diagnosed this year, based on recent estimates.
In the study, researchers examined about 69,000 men and women, and after about six years, 566 had developed melanoma.
Among the 59,000 people in the study who had never taken vitamin A supplements, there were 506 cases of melanoma, while among the 5,800 people who were currently taking it and had used it regularly over the past 10 years, there were 28 cases.
Study researcher Dr. Maryam Asgari, a dermatologist and research scientist at Kaiser Permanente in Oakland, said the protective effect might be stronger in women than men because men may be more susceptible to skin damage from ultraviolet radiation.
She pointed to a recent animal study that suggests females may have more natural antioxidant protection in the skin than males.
The new study also found the melanoma risk was reduced the most in those who took high doses of the supplement. But Asgari cautioned that taking too much vitamin A could lead to such harmful conditions as birth defects, liver problems and bone loss.
"There are limits to how much vitamin A a person can consume," she said.
The recommended daily amount of vitamin A is 700 micrograms for adult women and 900 micrograms for adult men, according to the National Institutes of Health. Taking more than 2,800 micrograms of vitamin A could lead to toxic symptoms in adults.
Reducing sunlight exposure has long been recommended to reduce the risk of melanoma. This includes limiting time in direct sunlight, wearing sun block and avoiding tanning beds.
Unfortunately, not all melanoma is a result of sun exposure. There is also a strong genetic component, Mercurio said. "Even the most vigilant sun-avoider is at risk, especially if they are fair-skinned, freckle easily and have red or blonde hair."
Although she said the study's findings were compelling, she cautioned it's not clear how much vitamin A might bring a benefit.
"We don't know yet the optimal dosage," Mercurio said. "Further studies will clarify how much vitamin A in the form of a supplement would be of benefit for melanoma prevention."
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