For most former smokers who quit at least 15 years ago, the risks of heart failure and death are the same as those of someone who never smoked, according to a new U.S. study.

“These results support the majority of literature, including that of the U.S. Surgeon General,” said senior author Dr. Ali Ahmed of the Center for Health and Aging at the Washington DC VA Medical Center.

But those who were heavy smokers – meaning at least a pack a day for 32 years or more - do still have an elevated risk, even after 15 years, which was a surprise, Ahmed told Reuters Health by email.

“While all individuals who quit smoking will benefit from a decreased chance of death, to achieve the full complement of health benefits of smoking cessation of one who has never smoked, smokers need to smoke less and quit early, and for those are not smokers – never start smoking,” he said.

Ahmed and his coauthors used the ongoing Cardiovascular Health Study of adults over age 65, which included 2556 people who had never smoked, 629 current smokers and 1297 former smokers who had quit at least 15 years earlier. Of those who had quit, 312 had been heavy smokers, with 32 “pack-years” or more of smoking.

After 13 years of follow-up, about 21 percent of never smokers and 21 percent of former smokers experienced heart failure. But among former smokers with at least 32 pack-years, almost 30 percent suffered heart failure.

When the researchers accounted for other factors like age, sex, race, education, other health conditions and medications, current smokers were about 50 percent more likely to have heart failure than never smokers or former smokers, as reported in Circulation: Heart Failure.

Over the same time period, current smokers were twice as likely to die from any cause, compared to never-smokers, and former heavy smokers were about 26 percent more likely than never-smokers to die.

“When one smokes, it induces atherosclerosis, or the buildup of plaque in the arteries,” which narrows the arteries and increases the risk of blood clot or heart attack, Ahmed said. “However, when one quits smoking, the buildup of plaque and risk of blood of clots decreases, allowing one’s cardiovascular risk to return to normal over time.”

“To date, this is the first study that investigated the role of amount and duration of prior smoking on the health benefits of prolonged cessation for former smokers,” said Dr. Gerasimos Siasos of Brigham and Women's Hospital in Boston, Massachusetts, who was not part of the study.

Former heavy smokers may not achieve the health profile of never smokers, but the cardiovascular risk for them is definitely lower compared to current smokers, Siasos told Reuters Health by email.

Quitting smoking also reduces the risk of lung cancer and other cancers of the upper gastrointestinal tract, said Bich Tran, a public health and epidemiology researcher at the University of New South Wales in Sydney, Australia. Tran was also not involved in the new study.