Each volunteer was exposed to a pulse of UV radiation on small patches of their skin (less than 1 inch in diameter) that were either treated or untreated with different doses of broccoli extract.
The researchers found that the degree of skin redness (erythema) caused by UV rays, which is an accurate index of the inflammation and cell damage caused by UV radiation, is markedly reduced when treated with the extract.
At the highest doses, UV-induced redness and inflammation were reduced by an average of 37 percent. The extracts were protective even when applied three days prior to UV exposure. The protection did vary considerably among the subjects, ranging from 8 percent to 78 percent.
Lead researcher Paul Talalay, M.D., professor of pharmacology, more importantly revealed that the extract is not a sunscreen. Sunscreens work by absorbing UV light and preventing its entry into the skin. This extract on the other hand, works inside cells by boosting the production of a network of protective enzymes that defend cells against many aspects of UV damage.
As a result, the effects are long lasting. The protection lasts for several days, even after the extract is no longer present on or in the skin. Talalay says: "Treatment with this broccoli sprout extract might be another protective measure that alleviates the skin damage caused by UV radiation and thereby decreases our long-term risk of developing cancer."
The protective chemical agent in the broccoli sprout extracts is sulforaphane. It was first identified by Talalay and his colleagues more than 15 years ago and has been shown to prevent tumor development in a number of animals treated with cancer-causing chemicals.
The study appears in this week's issue of the Proceedings of the National Academy of Sciences.