Kenfield said many of the women she had interviewed reported a quick improvement in quality of life. "There is definitely an immediate benefit of quitting, such as being able to breathe better because you have less carbon monoxide," she said. "Your heart rate goes down, your blood pressure goes down, you have better circulation."
Making inroads into chronic diseases is more complicated.
Smoking damages the cardiovascular system in several ways. It interferes with natural chemicals that keep blood vessels open and prevent harmful clots. It also reduces levels of good cholesterol and makes bad cholesterol more likely to do harm.
"You stop smoking, and basically you're reversing this process," said Dr. Michael Miller, director of preventive cardiology at the University of Maryland Medical Center. "It's like taking away a natural stimulant."
Years of smoking subjects the lungs to carcinogens that can damage the DNA in cells. For a single cell to turn cancerous, it takes an accumulation of genetic changes - a process that occurs over time.
"By stopping, you don't accumulate more damage," said Dr. James Hermann, an associate professor of oncology at the Johns Hopkins Kimmel Cancer Center. "There's still some damage that's occurred in some of the smokers already, but at least you don't incur more."
Some may quit in time to prevent the final insult that tips a cell into a cancerous state. For some, quitting may come too late: The final injury has already occurred, even though the person might not yet have symptoms. But as a general rule, "The longer you've quit, the better; the less you've smoked, the better," Hermann said.
The Harvard researchers calculated the risk of dying according to the severity of a person's smoking habit. Women with a 40-year habit of at least 35 cigarettes (almost two packs) a day were 114 times more likely to die of emphysema or chronic bronchitis than nonsmokers. If they smoked fewer than 15 cigarettes daily, their risk was 23 times that of a nonsmoker.
Women who smoked 35 cigarettes daily were 40 times as likely to die of lung cancer and almost five times as likely to die of a heart attack as nonsmokers. If they smoked the lesser number, they were almost 12 times as likely to die of lung cancer, and three times as likely to die of a heart attack.
Meanwhile, researchers from Rockville-based Nabi Biopharmaceuticals reported results of a six-month trial yesterday at the annual vaccine conference of the National Foundation for Infectious Diseases in Baltimore.
The vaccine, called NicVAX, is designed to trigger antibodies that bind to nicotine as it enters the bloodstream. Together, the antibodies act like a giant sponge, soaking up nicotine before it binds. In the trial, 301 volunteers were given five injections over six months and had their smoking habits tracked for a year.
Sixteen percent of the 201 volunteers who got the medication managed to quit smoking for a full year, compared with only 6 percent of the 100 volunteers given a placebo, company officials said.
A booster shot might be necessary if people get nicotine cravings after extended periods, a company official said.
The company expects to begin a larger trial later this year and seek government approval sometime after that for a product that would be given in a doctor's office.
jonathan.bor@baltsun.com
Sun reporter Dennis O'Brien contributed to this article.
