The findings hold important implications for smokers as well as the clinicians who are trying to help them quit.
"The human body really is a miracle. It knows when it is not getting what it's used to, and it automatically does something about it," says Karen Ahijevych, an associate professor of nursing and a member of The Ohio State University Comprehensive Cancer Center – Arthur G. James Cancer Hospital and Richard J. Solove Research Institute.
The findings appear in the April issue of Pharmacology, Biochemistry & Behavior.
Ahijevych and her research team studied 25 women over six days in three different situations: smoking their usual amount, restricted intake (50 percent) and increased intake (167 percent). Thirteen of the women were black and 12 were white. The women smoked their regular brands of cigarettes and researchers noted levels of carbon monoxide (CO) and cotinine in the participants' blood before and after four of the cigarettes each day. Carbon monoxide reflects general exposure to hundreds of toxins and carcinogens in smoke while cotinine, a metabolite of nicotine, reveals how much nicotine has been absorbed over time.
The scientists also carefully observed the way the women smoked – scientists call it "smoking topography" – measuring such things as the number and size of the puffs per cigarette, the length of time between puffs and how much of the cigarette was smoked before it was extinguished.
Researchers discovered that, generally, when women smoked in a restricted environment, they took larger drags and smoked more of the cigarette before putting it out. In addition, when smoking fewer cigarettes, the women produced more CO in their exhaled air per cigarette, compared to when they smoked their regular number of cigarettes or increased use.
Higher CO and nicotine boosts were especially pronounced among women who were defined as efficient smokers – those who normally register high levels of cotinine per cigarette with regular smoking ( more than 20 nanograms per millileter of blood.)
"We were surprised at how much the very efficient smokers could increase their levels of CO and nicotine even further," says Ahijevych. "And the interesting thing is that most of these women were totally unaware that they were changing the way they were smoking to make up for fewer cigarettes."
There appeared to be differences in ethnicity as well, with black women registering higher percentage increases of carbon monoxide levels across all smoking situations, compared to whites. Ahijevych says this may be due to the fact that all of the black women smoked menthol cigarettes, and menthol smokers tend to inhale greater amounts of smoke because it is somewhat easier to take in, compared to non-mentholated smoke.
Researchers also found that black menthol smokers had higher carbon monoxide levels compared to white smokers in a restricted environment. Because both black and white menthol smokers registered higher CO levels that white non-menthol smokers, however, Ahijevych concludes there is a potential influence of menthol regardless of race.
"There are a lot of social pressures on smokers to quit these days," says Ahijevych. "Workplaces and restaurants are increasingly adopting bans on smoking, and we know that as taxes on tobacco increase, sales drop off. Millions of people want to quit, and they often see cutting back as the first step in a long-term strategy. Unfortunately, our research suggests that this may be giving them a false sense of security."
Ahijevych, who has been studying smoking cessation for sixteen years, says the best way to quit is through the use of pharmacotherapy – a broad reference that includes various patches, gums and other prescription items that can help offset craving.
"The bottom line for smokers is to be aware that just because they smoke 12 cigarettes a day instead of 20 doesn't mean that they are less dependent on tobacco," says Ahijevych. "As clinicians, we need to understand that a person who smokes half a pack a day may be just as dependent as a person who smokes a whole lot more, and may need an equally aggressive treatment plan."
Study co-authors include Harrison Weed and Jo Clarke.
The National Institute of Drug Abuse/NIH funded the study. Researchers also had support from the General Clinical Research Center at Ohio State.
The Ohio State University Comprehensive Cancer Center is a network of interdisciplinary research programs with over 200 investigators in 13 colleges across the OSU campus, the Arthur G. James Cancer Hospital and Richard J. Solove Research Institute and Children's Hospital, in Columbus. OSUCCC members conduct research on the prevention, detection, diagnosis and treatment of cancer, generating over $75 million annually in external funding.