A study published this week shows that taking vitamin A supplements may be able to decrease the risk of developing melanoma. Maryam M. Asgari of the University of California in San Francisco and coauthors show that taking retinol, a form of vitamin A results in chemoprotection against melanoma. The study is published in the Journal of Investigative Dermatology.
After an average of 5.84 years of follow-up, doses greater than 1,200 µg per day were associated with a significant reduction in melanoma risk, 40% and 26%, respectively. No association of melanoma risk and dietary vitamin A intake was seen in the study. The effect is limited to those who took vitamin A in excess of standard multivitamin guidelines and was more pronounced in women than in men.
Vitamin A is a fat-soluble vitamin that is an essential nutrient that cannot be synthesized by humans. The main source of vitamin A in the diet is from animal products: liver, eggs, and milk. Plant based provitamin A carotenoids such as beta carotene can convert to retinol in the intestine, and serve as an additional source of the nutrient. Vitamin A is necessary for healthy cell growth and differentiation.
Intake of beta carotene, either in the diet or as a supplement was not seen to have an effect on melanoma risk. The authors note that beta carotene has approximately one-twelfth of the vitamin A activity compared with retinol.
The VITAL cohort, 69,635 individuals, is the only large, prospective study that has looked specifically at the association of dietary supplements and cancer risk. Mouse models had shown that retinol and its related compounds can decrease the size of a melanoma tumor and improve survival in mice with melanoma.
The average age of the subjects was 62 years, women made up 52% of the cohort.
Men were more likely to develop primary cutaneous melanoma during the follow-up tracking period, to have fair skin, red or blond hair, have a predisposition to burn with exposure to the sun, and were more likely to have had a personal or family history of melanoma.
The protective effect looks to be specific for retinol, because the intake of carotenoids and other related compounds was not associated with a reduced melanoma risk, according to the authors.
Asgari and coauthors believe that the disparity seen between men and women may be due to fundamental gender differences that have been observed before, where women have more favorable outcomes. However, the study cannot rule out that the result occurred by chance.
The authors suggest that gender and sun exposure may also affect how retinol might prevent melanoma, as there were stronger protective effects in women and in sun-exposed sites.
Caveat of the study include the lack of assessment of known melanoma risk factors such as the number of nevi and the lack of data on serum levels of retinol or carotenoid levels of the subjects. However, based on the significant results, they suggest that vitamin A supplements could be promising as a chemopreventive agent for melanoma.