Toronto, ON -- (SBWIRE) -- 05/08/2014 -- In fact, nicotine dependence has risen 12 percent from 1989 to 2006, and the number of highly nicotine-dependent people has gone up 32 percent, according to research expected to be presented Tuesday at the American College of Chest Physicians annual meeting, in Philadelphia.

Nicotine dependence can vary from smoker to smoker, experts noted.

"My clinical perception has been that over the last five years, patients that I am seeing require much more intensive treatment because tobacco dependence is more severe," said lead researcher Dr. David P. Sachs, from the Palo Alto Center for Pulmonary Disease Prevention in California.

Studies have shown that the more nicotine-dependent an individual is, the less effective standard treatment will be, Sachs said. "These people will suffer severe nicotine withdrawal symptoms, and they will be more likely to relapse back to cigarette use," he explained.

For the study, Sachs' team compared the degree of nicotine dependence between 1989 and 2006 in three groups of smokers, a total of 630 in all, who enrolled in smoking cessation programs.

Nicotine dependence was measured using the Fagerstrom Tolerance Questionnaire, which assesses nicotine dependence on a scale of 0 to 11 points.

Over 15 years, scores on the questionnaire increased by 12 percent, and the number of people with scores of 7 to 11 went up 32 percent. Overall, the proportion of people who were highly nicotine-dependent rose from 55.5 percent to 73 percent over the study period, Sachs' group found.

Sachs believes that it's the most nicotine-dependent smokers who are now showing up at quit-smoking programs. "If these patients are going to get effective treatment and not be at risk for relapse, they need more intensive treatment," he said.

About 10 percent of smokers are actually not nicotine-dependent, Sachs said. "These are smokers who can stop 'cold turkey' and not experience physical nicotine withdrawal symptoms. It's really a matter of willpower for them," he said.

Once those smokers have stopped, "that leaves the people who are genetically dependent on nicotine," Sachs said.

Dr. Norman H. Edelman is a professor of preventive medicine, internal medicine, physiology and biophysics at Stony Brook University in New York and chief medical officer of the American Lung Association. He said there could be several explanations for the increase in degree of nicotine dependence among current smokers.

"I agree with the author's conclusions with regard to increasing difficulty to be expected in achieving smoking cessation," Edelman said. "This may be the reason rates of smoking cessation have been declining."

There may, however, be other reasons for the increase in nicotine dependence, Edelman said. "Is the reason for the increase in nicotine addiction due to the fact that cigarette companies have been increasing the nicotine content of cigarettes? Is the reason for this finding the fact that we have been successful with the less-addicted, and now have the more addicted 'hard-core' [smokers] left?" he asked.

In another study, also expected to be presented at the meeting Tuesday, U.S. Navy researcher Michael A. Wilson reported that the prevalence of smoking among Marines and sailors serving in Iraq is more than two times the U.S. average.

Wilson found that of 408 Marines and sailors in Iraq, 64 percent used some form of tobacco, much higher than the U.S. national average for tobacco use (29.6 percent), and a big jump from the 38.9 percent of troops using tobacco in a similar survey conducted in 2004.

Cigarette smoking accounted for 52 percent of tobacco use, followed by smokeless tobacco (36 percent) and the use of both (24 percent). Most of the troops surveyed (74 percent) said they wanted to quit.

The long-term consequences of increased smoking are worrisome, Wilson warned. "This study indicates the prevalence of tobacco abuse in combat units deployed to Iraq is substantially higher than the national average," he wrote. "Such abuse will likely cause a greater negative impact on the long-term health of U.S. veterans than combat-related injuries and will have great financial consequences for both VA and U.S. health-care systems," he concluded.