Dark-skinned smokers may be at greater risk for nicotine addiction than their paler counterparts, a new study finds.

Researchers found that in African Americans, darker skin — specifically that acquired by sun exposure, not genetics — is directly linked to smoking frequency and dependence.

"African Americans are known to have a more difficult time quitting and suffer from more tobacco-related diseases," said Gary King, a medical sociologist at Pennsylvania State University and lead author of the study, published in Pharmacology, Biochemistry and Behavior. "By addressing the connection between biological aspects of skin color and tobacco use, this has global implications for all groups, especially to populations with high levels of UV radiation."

Melanin pigments, which determine skin color, bind tightly to nicotine. As a consequence, nicotine and tobacco's cancer-causing agents tend to linger and accumulate in other melanin-containing tissues like the heart, lungs, liver and brain, potentially putting those organs at increased risk for tobacco-related diseases. This study is the first to explore the relationship between skin melanin levels and smoking behavior, said King.

The more melanin, the browner the skin. But there's more than one way to get there. Melanin levels are genetically determined, but they can also be increased by exposure to the sun or other sources of ultraviolet rays, like tanning beds. Though both kinds of melanin are molecularly indistinguishable, King wanted to know if they had different effects on smoking behaviors.

He evaluated African American smokers from inner city Harrisburg, Pennsylvania. He measured the color of the skin on their foreheads, which is controlled by both genes and the sun, and on their inner arms, which should result primarily from genetics. He then quantified the smokers' average number of cigarettes per day and nicotine dependence.

King's team found that the darkness of the forehead was positively correlated to the number of cigarettes smoked per day as well as nicotine dependence, while darkness of the inner arm did not demonstrate this link. King says the mechanism is unclear, but he thinks people with higher levels of melanin in the skin would accumulate higher levels of nicotine, which might leach into the bloodstream and travel to nicotine receptors in the brain. Low levels of nicotine constantly coursing through the body might make it easier to develop a dependence.

As skin darkness also has has been shown to have links to racial discrimination, King also surveyed the participants for stress levels, perception of racial discrimination and attitudes toward race and health. He found no links to smoking frequency or dependence, though he acknowledged that other studies have found this correlation.

King hopes the findings will help understand why African American smokers have a more difficult time quitting than Caucasians, and are disproportionately affected by smoking-related diseases.

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Image: Flickr/nasrulekram

Citation: "Link between facultative melanin and tobacco use among African American," by Gary King, Valerie B. Yerger, Guy-Lucien Whembolua, Robert B. Bendel, Rick Kittles and Eric T. Moolchan. Pharmacology, Biochemistry and Behavior. Volume 92, Issue 4, June 2009.