Broccoli not replacing sunscreen any time soon
Broccoli could prevent skin cancer, reported the Daily Mail and other newspapers on October 23 2007. The extract from the vegetable “could be better protection against skin cancer than sunscreen”, when applied to the skin, the newspaper said. The broccoli extract works by increasing the protective enzymes in the skin, rather than by absorbing the ultraviolet light (UV) from the sun’s rays – which is how sunscreens work. The Daily Telegraph reported that “conventional sunscreens used in the same experiments were essentially ineffective”.
This story is based on a small experimental study that looked at whether applying an extract of broccoli to the skin protected against the reddening effects of UV. The study did not look at whether the extract protected against skin cancer. Instead it monitored the reddening of the skin that occurs in response to UV exposure. The levels of certain proteins that are involved in the skin’s response to UV were also investigated. Although this study highlights an area for future research, much larger studies will be needed to see whether this extract can protect human skin against the DNA damage caused by UV, and whether it is any better or more convenient than any of the other skin protection products available.
Where did the story come from?
Dr Paul Talalay and colleagues from The Johns Hopkins University in the US carried out this research. The study was funded by the American Cancer Society, National Institutes of Health, American Institute for Cancer Research and the Lewis B and Dorothy Cullman Foundation. Some of the authors act as unpaid consultants to Brassica Protection Products (BPP), a company that produces broccoli sprouts, the son of one of the authors is CEO of BPP, and The Johns Hopkins University is an equity owner of BPP. The study was published in the peer-reviewed scientific journal Proceedings of the National Academy of Sciences of the United States of America.
What kind of scientific study was this?
This was an experimental study. Researchers first looked at how to assess the effects of UV radiation on skin and then looked at the effects on the skins of mice and humans of broccoli sprout extract. They also looked at the effect it had, if any, on the skin’s reaction to UV.
The researchers looked whether the development of redness in human skin was a good measure of UV damage. They recruited five adult volunteers with different skin types (types 1, 2, and 3) who had no skin diseases. They asked volunteers not to eat cruciferous plants (cabbage, broccoli, brussel sprouts and so on, including mustard, horseradish, and wasabi) for a week before the study and during the study. Researchers found that test areas on a volunteer’s back reddened a similar amount in response to the same dose of UV, but that different areas on the same person’s back reddened differently. When increasing doses of UV were applied, the redness increased. This led them to conclude that they could use this test to measure any protective effects of broccoli.
In the second part of the study, researchers looked at the effects of an extract made from three-day-old broccoli sprouts, which are rich in the chemical sulforaphane, on human skin. They applied the extract to three small areas of the lower back on three volunteers at 24-hour intervals, with each area receiving one application, two applications, or three applications. They then took a biopsy sample of the skin to look at which dose had the greatest effect on a particular protein that helps to protect cells from the effects of UV light.
The researchers then looked at the protective effects of different doses of broccoli sprout extract by applying the doses to one volunteer on three successive days and then assessing the redness that resulted from exposure to UV. In another volunteer, they used different doses of UV and applied the extract to four different spots on the volunteer’s back, each with a corresponding area treated with solvent alone, and these were exposed to eight different doses of UV. They repeated this experiment on six further volunteers using different doses of the extract.
Finally, they looked at whether applying the extract would have a lasting effect by applying the extract to one person’s skin and then exposing them to UV either 48 or 72 hours after the application and looking at the reddening.
What were the results of the study?
The researchers found that applying broccoli sprout extract to the skin on three consecutive days resulted in the greatest increase in protein levels in three volunteers, so this dose was used in subsequent experiments.
They found that applying increasing doses of the broccoli sprout extract gave increasing protection against skin reddening when exposed to UV in the one volunteer tested. The broccoli extract reduced the increase in redness that was expected in response to increasing doses of UV, and this reduction appeared to be relatively consistent for the six higher UV doses.
The extract reduced redness significantly more than the solvent alone (control). On average, the extract reduced redness by about 38%. They found that the extract could reduce redness even if applied two or three days before UV exposure, in the one volunteer tested, although the reduction in redness was less than that seen when UV exposure came within 24 hours of applying the extract.
What interpretations did the researchers draw from these results?
They concluded that the broccoli extract protects human skin against UV radiation, and this protection is long lasting, a feature they say has not been shown for other forms of UV protection that are applied to the skin.
What does the NHS Knowledge Service make of this study?
This experimental study was carried out in a very small number of people. Before any conclusions about the effects of broccoli extract in protecting human skin from UV can be drawn, much larger studies will be needed. This study used redness as its measure of UV damage, but future studies will be needed to show that the extract also prevents damage to the DNA that is a known effect of UV. It is this cellular event that leads to the development of skin cancer. This study also cannot say whether eating broccoli (rather than applying the extract to the skin) will protect against sun-related skin damage, and people should continue to take standard precautions to avoid exposing their skin to damaging UV rays.
Sir Muir Gray adds...
Broccoli is my favourite green veg; there are already plenty of good reasons to eat it and this might be another one. However, people should not reduce the traditional sun-protective practices (slip, slop and slap) on the strength of an extra spoonful of broccoli.
