Scientists have worked out how caffeine might protect against certain skin cancers – a finding that could lead to better sunscreens.
The research, conducted in mice, suggests that caffeine changes the activity of a gene involved in the destruction of cells that have DNA damage and are therefore more likely to become cancerous. The scientists said this may lead to new ways of preventing skin cancer, though other experts cautioned that it did not mean coffee lovers were better protected against the disease.
Skin cancer is a common disease. According to Cancer Research UK, around 100,000 cases of non-melanoma were registered in the UK in 2008, and just under 12,000 cases of the more dangerous malignant melanoma. These cancers can be caused by over-exposure to ultraviolet light from the sun, which can damage the DNA of skin cells, leading to errors when the cells divide.
The overall protective role of caffeine against cancers has been noted in previous studies, but Allan Conney of the department of chemical biology at Rutgers University in New Jersey wanted to find the specific molecular mechanisms behind it. He suspected that the response might involve a gene called ATR, which is suppressed when caffeine molecules are around. This suppression encourages the death of DNA-damaged cells.
Conney tested the idea by creating genetically modified mice whose ATR genes were deficient and exposing them to ultraviolet light until they developed skin cancer. After 19 weeks of UV exposure, he found that these mice developed 69% fewer tumours than those that had fully functioning ATR genes. In addition, tumours in the GM mice developed three weeks later than in standard mice.
After 34 weeks of UV exposure, all the mice had developed tumours, mainly a type of non-melanoma cancer called squamous cell carcinoma (SCC). The results were published on Monday in the Proceedings of the National Academy of Sciences.
"All of this suggests the possibility that caffeine, possibly [applied to the skin], would have an inhibitory effect on sunlight-induced skin cancer," said Conney. "In addition to the effects on the ATR pathway, caffeine also has sunscreening properties."
SCCs are less common than the other type of non-melanoma cancer, called basal cell carcinomas, but it's the former that are more dangerous. "People rarely die from basal cell carcinomas, but you need more invasive cutting to get it out," said Conney. "There's more disfiguration with basal cell than squamous cell. It's the squamous cell cancers that can metastasise and are more dangerous."
Jessica Harris, a health information manager at Cancer Research UK, pointed out that Conney's study examined how caffeine affected genes when it was directly applied to the skin, rather than ingested. "It didn't look at the effects of drinking coffee, so doesn't tell us whether or not this could reduce the risk of skin cancer," she said.
Studies looking at coffee consumption and cancer in large groups of people have provided mixed results, she added. "Some have found that coffee drinking may slightly reduce the risk of certain types of cancer, but the evidence is not yet strong enough to be certain, and these effects tend to be seen among people who drink very large amounts."
The best way to reduce the risk of skin cancer, said Harris, "is to enjoy the sun safely, taking care not to burn by using a combination of shade, clothing and sunscreen."
Dot Bennett, a professor of cell biology at St George's, University of London, said that any move to add caffeine or related molecules to sunscreens should be undertaken with care. "First one might want to check there is no adverse effect of caffeine on the incidence of other cancers, especially melanoma (pigmented skin cancer), which kills over four times as many people as [squamous cell carcinoma]. But caffeine lotion might promote tanning a little, since this family of molecules stimulates pigment cells to make more pigment."
