That refreshing glass of iced coffee or iced tea might do more than cool you off in the summer heat. A new study of nearly 113,000 men and women found a link between those who took in the most caffeine and a lower risk of the most common type of skin cancer.

About 1 in 5 Americans will develop skin cancer in their lifetime, and 4 out of 5 of them will be diagnosed with basal cell carcinoma, according to the researchers. The number of new cases is increasing by 4% to 8% each year, suggesting that basal cell carcinoma will soon be as common as all other cancers combined, they write.

The three most common types of skin cancer are basal cell, squamous cell, and melanoma. Basal cell can often be cured, and melanoma is the deadliest.

The researchers followed women from the Nurses' Health Study and men from the Health Professionals Follow-Up Study. Every other year, study participants completed mailed questionnaires with the latest information about their lifestyle, diet, and medical history. And every questionnaire asked participants how frequently they had consumed caffeinated and decaf coffee, tea, cola, and chocolate in the previous two years.

The researchers collected 24 years' worth of information from 72,921 women and 22 years' worth from 39,976 men. Coffee was by far the most common source of caffeine.

After taking into account other factors related to skin cancer risk, such as the number of severe sunburns and natural hair color, the researchers found that women who ate or drank the most caffeine had an 18% lower risk of basal cell skin cancer than women who ate or drank the least. In men, the biggest caffeine consumers had a 13% lower risk of basal cell carcinoma than those who consumed the least.

No Link to Risk of Other Skin Cancers

The researchers did not find an association between caffeine intake and risk of squamous cell skin cancer, although animal studies have suggested such a link. But only 1,953 squamous cell cancers were diagnosed -- compared to 22,786 basal cell cancers -- so there might not have been enough cases to show a relationship to caffeine intake, researcher Jiali Han, PhD, says.

With another 10 years of follow-up, though, he and his colleagues might observe a difference in squamous cell cancer risk between the highest and lowest levels of caffeine consumption, Han says.

Caffeine intake was not associated with a lower risk of melanoma, the deadliest and least common of the three major types of skin cancer. There were only 741 cases of melanoma among the study participants.

Decaf coffee was not associated with a lower risk of skin cancer, so, Han says, "most likely we think [reduced skin cancer risk] is due to caffeine."

Mouse studies in which the animals received caffeinated water to drink have also linked the compound to a lower risk of skin cancer, says Han, an epidemiologist at the Harvard School of Public Health and Brigham and Women's Hospital.

And other studies in which caffeine was applied to the skin of mice have also found a connection to a lower skin cancer risk. The mouse studies have shown that caffeine promotes the elimination of skin cells damaged by ultraviolet light before they have a chance to develop into tumors.

"I'm not recommending people drink coffee only because of this paper," Han says, although he noted that other studies have shown that the beverage is linked to a decreased risk of diabetes, certain cancers, and Parkinson's disease. Linked is a key word with this type of research. Although this type of study can show a strong association between caffeine and skin cancer, it cannot prove cause and effect.

And, Han says, he's not advising that people drink coffee and then bake at the beach. The best way to prevent skin cancer is to minimize exposure to ultraviolet light from the sun or tanning booths, he says.
A Little Caffeine With Your Sunscreen?

Because topical caffeine reduces the risk of skin cancer in mice, should you expect to see a line of "Coffee-tone" sunscreen products any time soon? Some pricey sunscreens already list caffeine among their ingredients.

"It's not been studied carefully," says Allan Conney, PhD, a toxicology professor at Rutgers who's conducted research into the relationship between topical and oral caffeine and skin cancer in mice. "We've been trying to interest some of the major companies to put caffeine into products and do some studies."

Adding caffeine to sunscreen wouldn't be difficult, Conney says, but no company has yet expressed willingness to invest the time and money into clinical trials required to convince the FDA to allow a claim of reduced skin cancer risk.

Han's study appears in Cancer Research.