As if you needed another reason to eat chocolate, German researchers have shown that ingesting types rich in cocoa solids and flavonoids—dark chocolate—can fight skin cancer. Their findings are preliminary because they come from a trial of just 24 women who were recruited to add cocoa to their breakfasts every day for about 3 months.
Half the women drank hot cocoa containing a hefty dose of flavonoids, natural plant-based antioxidants that research has suggested prevent heart attacks. The remaining volunteers got cocoa that looked and tasted the same but that had relatively little of the flavonoids. At the beginning and end of the trial, Wilhelm Stahl of Heinrich-Heine University in Düsseldorf and his colleagues conducted a host of tests on each volunteer. One assessment involved irradiating each woman's skin with slightly more ultraviolet (UV) light than had turned her skin red before the trial began.
The skin of the women who had received the flavonoid-rich cocoa did not redden nearly as much as did the skin of recruits who had drunk the flavonoid-poor beverage. Women getting the abundant flavonoids also had skin that was smoother and moister than that of the other women.
Overexposure to UV light can foster the development of skin cancer. A dietary source of skin protection might offer some innate defense for sunny days when an individual doesn't use sunscreen, Stahl's team says.
Chocolate, these scientists note, is just the latest in a range of antioxidant-rich foods holding the potential to shield skin from sun damage. For nearly a decade, Stahl's group has conducted studies with cooked tomato products showing that their ingestion, too, can limit UV-induced skin reddening. Pigmented molecules called carotenoids—especially the one known as lycopene—appeared responsible for tomato's skin-protection benefit (see Dietary protection against sunburn (with recipe)).
Many of the carotenoids in tomatoes are powerful antioxidants that can quash free radicals. These are the molecular fragments that can cause biological havoc when they rip electrons from other molecules. Because many flavonoids also function as potent antioxidants, Stahl's team decided to investigate whether substances in chocolate might offer skin protection.
The researchers recruited women between the ages of 18 and 65. Each volunteer received packets of a dry powder to mix each day with 100 milliliters of hot water—roughly a half cup. Half of the women received powder containing 329 milligrams of flavanols, a type of flavonoid, per serving. The rest got powder delivering a mere 27 mg of flavanols per serving. The primary flavanols were epicatechin and catechin.
Mars Inc., the candy company that has been experimenting with dark-chocolate products rich in flavonoids, supplied the cocoa powder and partially funded the experiment. Harold H. Schmitz, the company's chief science officer, claims that the proprietary recipe for the product retains nearly all of the natural-cocoa flavonoids that most chocolate processing cooks and washes out.
In the June Journal of Nutrition, Stahl's team reports that the women drinking the high-flavonoid cocoa had 15 percent less skin reddening from UV light after 6 weeks of cocoa consumption and 25 percent less after 12 weeks of the trial. Both figures are comparisons with the same women's response to UV light before the study started. The women drinking the cocoa with low flavonoids showed no change during the trial.
Most flavonoids absorb UV light, and this probably played a role in the skin effect, the researchers say. However, they add, skin reddening is also an inflammatory response, and other researchers have linked consumption of flavonoids to ratcheting down the body's synthesis of inflammatory agents.
For the women getting larger doses of flavonoids, blood flow in the skin doubled over the course of the trial in tissue 1 millimeter below the surface, and increased by 37.5 percent in tissue 7 to 8 mm deep. Similar improvements in blood flow through big blood vessels have been witnessed after people have eaten dark chocolate (see Cardiovascular Showdown—Chocolate vs. Coffee).
Moreover, after 12 weeks of consuming the flavanol-rich cocoa, the women's skin was 16 percent denser, 11 percent thicker, 13 percent moister, 30 percent less rough, and 42 percent less scaly than it was at the beginning of the experiment. Although the mechanism for most of these benefits remains unclear, the Düsseldorf researchers suspect that improved blood flow was a contributor.
Mars' Schmitz agrees. "People don't think about it, but in reality your skin, just like every other tissue, depends on healthy blood flow. And in our previous work ... we showed that blood flow in the extremities—the finger tip—was improved" in people receiving cocoa flavonoids. So, he argues, "it wasn't a shot in the dark" to hypothesize that cocoa ingestion might improve overall skin condition and health. Yet, he adds, "I was still surprised to see this."
If follow-up studies confirm these skin-health data, he says, "you're talking about being able to make people look better." He adds, "We did not go into this study with the intention to create a skin-health product, but it now looks like maybe we've got one."
Not just any chocolate
Could a person realistically add enough flavonoids to his or her diet to produce the benefits suggested by the study? Flavonoid quantities in the richer cocoa were "similar to those found in 100 grams [a little over 3 ounces] of dark chocolate," Stahl's group reports.
The cocoa drink provided its flavonoids in a serving that delivered only about 50 calories—far below the 400 to 500 calories ordinarily encountered in candy providing a walloping dose of flavanols. Schmitz concludes that people can, in theory, get this efficacious dose without blimping out.
The rub is that the cocoa used in this study and in others by Mars isn't commercially available. If enough people pester the company for the cocoa, Schmitz says, "eventually we might have to offer such a product." In the meantime, he notes, the company offers a candy, CocoaVia, in flavanol-rich portions that deliver fewer than 100 calories per serving.
Targeting free radicals and more
The new skin-protection data are more than a curiosity, says Hasan Mukhtar, director of dermatology research at the University of Wisconsin–Madison. The results suggest, he says, that dietary flavonoids reach the upper layers of skin and "have the ability to counteract the oxygen free radicals generated as a consequence of exposure to UV radiation."
UV exposure leads not only to impaired immunity and accelerated aging in skin, but also to cancer, especially in light-skinned people, Mukhtar points out. Work by his group and others has shown that UV light triggers many reactions in the body that can lead to tissue damage.
In several papers, Mukhtar and his colleagues have found evidence that natural botanical antioxidants—such as those just tested in cocoa—can inhibit harmful, UV-triggered chemical pathways in the body.
In a study at the Case Western Reserve University School of Medicine, Mukhtar's group applied epicatechin-rich green-tea flavonoids to the skin of volunteers before irradiating the area with UV light. The researchers found that compared with the response of unprotected skin, the tea cut by 60 to 80 percent DNA changes known to play a role in immune suppression and skin cancer. The team noted that the treatment also prevented sunburn.
In the March-April Photochemistry and Photobiology, Mukhtar's team reports the results of treating cultured skin cells with pomegranate fruit extract, a substance rich in flavonoids. When irradiated with UV-light in a test tube, human cells in such an experiment usually undergo stress-induced inflammatory changes that can lead to cancer. However, the pomegranate extract dramatically inhibited those pre-carcinogenic changes.
Mukhtar points out that such data show that "not all of these agents affect the same signaling pathways." This suggests, he says, that eating a mix of flavonoid-rich foods may reinforce the UV protection by simultaneously acting on several potentially damaging processes. Some flavonoid treatments may even prove additive in their skin-protecting role, he says.
Chocolate's agents might offer important backup protection to some of the substances his group has been testing, says Mukhtar.
However, diet isn't the only means of getting these protective agents to the tissues that need them, Mukhtar suspects. He says it may make sense to add them to skin-care products.
That said, I'd prefer to get my protection from eating dark chocolate. Indeed, I look for any excuse to label as therapeutic my bittersweet indulgence.
Department of Dermatology
University of Wisconsin, Madison
Medical Sciences Center, Room B-25
1300 University Avenue
Madison, WI 53706
Harold H. Schmitz
Analytical and Applied Sciences
800 High Street
Hackettstown, NJ 07840
Institute for Biochemistry and Molecular Biology
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