According to scientists, broccoli contains a chemical called sulphoraphane, which activates cancer-fighting enzymes inside cells.  Researchers say the richest source of sulphoraphane is contained in sprouts.

In a demonstration of the plant’s anti-cancer properties, investigators smeared broccoli sprout extract on the skin of six volunteers for three days, and then exposed them to high doses of ultraviolet radiation, which is the leading cause of skin cancer.

They found there was an average 37 percent less redness and sunburn in the patches covered by broccoli extract.  Redness and sunburn are an indication of skin damage that could lead to cancer.

The results of the study are published in the journal Proceedings of the National Academy of Sciences.

Paul Talalay is a Johns Hopkins University molecular pharmacologist and the author of the study.  Talalay says sunscreen conferred no protection against the UV rays, but he says that does not mean people should stop using it.

“We want to avoid under all circumstances people doing weird things like making broccoli sprout soup and applying to their skin and thinking that they will be protected against the sun,” he said.  “They will have not have any protection whatsoever, because it’s a totally different mechanism and one cannot possibly substitute for the other.”

Applied as a thick cream, sunscreen protects the skin by deflecting the sun’s harmful rays.  But it must be constantly reapplied to remain effective.

In contrast, Talalay says, a compound made of broccoli sprouts works by penetrating skin cells and stimulating their natural cancer-fighting mechanism.

Observers call the research promising, but say more studies are needed because the results varied considerably among participants, ranging from a low of eight percent to a high of 78 percent protection against sunburn.  Talalay disagrees.

“Everybody knows you go to the beach and you get fried and I go to the beach and nothing happens to me,” he added.  “And we are in the same place.  So, the same experiment if done in a large number of individuals would be much more complex.  But I believe that the evidence certainly from animal studies is that we would get absolutely the same result.”

Talalay believes if it works in the skin, a sulphoraphane extract from broccoli sprouts is very likely to act as a hedge against cancer in other organs.

Meanwhile, researchers say there are a number of challenges in making a sun cream from broccoli sprouts, not the least of which is figuring out how to get rid of the green tint.

The American Cancer Society said it was looking for half a million volunteers willing to let researchers watch them for the next 20 years to see if they get cancer.

The aim is to match similar big studies in Europe and Asia that are looking on a large scale for the environmental and lifestyle factors that cause cancer, the second-leading cause of death in the United States after heart disease.

“This type of study involves hundreds of thousands of people, with diverse backgrounds, followed for many years, with collection of biological specimens and assessments of dietary, lifestyle and environmental exposures,” Eugenia Calle, managing director of analytic epidemiology at the American Cancer Society, said in a statement.

“It also requires active follow-up to discover if and when study participants develop cancer.”

The group will recruit men and women between the ages of 30 and 65 who have never been diagnosed with cancer. They will give blood to be tested and answer questionnaires at various times over the next 20 years.

Similar big studies have confirmed the link between cigarette smoking and lung cancer, shown that obesity increases the risk of several cancers, and linked aspirin use to a lower death rate from colon cancer.

They have also found evidence that defied conventional wisdom, such as the Women’s Health Initiative study that found hormone replacement therapy actually raises the risk of breast cancer, stroke and heart attack.