Skin color may point to possible susceptibility to nicotine dependence, say scientists at Penn State.
They believe that higher concentrations of melanin, the colour pigment in skin and hair, may be placing smokers with darker skins at increased susceptibility to nicotine dependence and tobacco-related carcinogens than lighter-skinned smokers.
"We have found that the concentration of melanin is directly related to the number of cigarettes smoked daily, levels of nicotine dependence, and nicotine exposure among African Americans," said Gary King, professor of Biobehavioral Health.
Studies conducted in the past have already shown that nicotine has a biochemical affinity for melanin, says the researcher.
He reckons that this association may lead to an accumulation of the addictive agent in melanin-containing tissues of smokers with greater amounts of skin pigmentation.
"The point of the study is that, if in fact, nicotine does bind to melanin, populations with high levels of melanin could indicate certain types of smoking behaviour, dependence, and health outcomes that will be different from those in less pigmented populations. And the addiction process may very well be longer and more severe," said King.
For their study, the researchers recruited 150 adult African American smokers from three sites in inner city Harrisburg during summer 2007.
The subjects provided the research team with the average number of cigarettes smoked each day, and answered a questionnaire that measured nicotine dependence - the Fagerstrom Test of Nicotine Dependence (FTND).
The researchers also measured amongst the smokers the levels of cotinine, a metabolic by-product of nicotine that can be used as a biomarker for tobacco use.
King and colleagues surmise that, along with tobacco toxicants, nicotine's half-life may be extended due to the accumulation in melanin-containing tissues.
Statistical analyses of data on the three measures of smoking-cigarettes per day, FTND score, and cotinine levels-along with a host of other variables including age, education and social demographics of the smokers, reveal that facultative melanin-the total amount of melanin acquired genetically plus the amount from the tanning effect of sunlight-is significantly linked to the number of cigarettes smoked per day as well as the FTND score.
This link was not observed with constitutive melanin, which is the amount of melanin solely acquired genetically.
King, however, insists that further research with larger samples of smokers is needed to obtain a clearer picture of the link between skin colour and nicotine addiction.
"We also think that studies conducted at different times of the year and in different geographic regions would help avoid seasonal variations such as the effect of tanning during summer. Additionally, nicotine levels could also be influenced by factors such as consumption of alcohol, amount of exercise, diet, body fat and stress. Future studies will have to control for these factors as well," King explained.
The findings appear in the June issue of the journal Pharmacology, Biochemistry and Behavior.