For young adults who smoke, the risk of a major heart attack is 8 times higher than for their peers who never smoked or who gave it up, a UK study found.

Older adults who smoke are also more likely than non-smokers their age to end up with heart attacks, researchers say.

Many people underestimate the health risks that come with smoking, said senior author Dr. Ever Grech, of the South Yorkshire Cardiothoracic Center at the Northern General Hospital in Sheffield.

"Many patients seem aware there are some risks of a heart attack with smoking, but they were blissfully unaware that the risks were anything more than slightly higher than usual," Grech told Reuters Health.

Smoking has been tied to an increased risk of cardiovascular problems since the 1950s, Grech and his colleagues write in the journal Heart. Smokers have heart attacks at younger ages, but no study has looked at the incidence of heart attacks among young smokers in a local population.

For the new study, the researchers used data collected between 2009 and 2012 on people over age 18 in South Yorkshire. The population included 1,727 individuals who were treated for STEMIs, which are major heart attacks caused by a blockage in one of the heart's main arteries. About 49 percent of the STEMI patients were current smokers, about 27 percent were ex-smokers and about 24 percent were never smokers.

Applying the results to the South Yorkshire population, the researchers calculated that in a group of 100,000 people, 60 smokers under age 50 would have a heart attack every year, compared to a combined total of 7 never-smokers and former smokers in that age group.

The difference is equal to about an eight-fold increase in risk for young smokers, compared to non-smokers.

Likewise, the researchers found about a five-fold increase in risk among smokers ages 50 to 65 years and about a three-fold increase in risk among smokers over age 65 years, compared to their non-smoking peers.

Grech said the findings confirmed his observations from working in a cardiac catheterization laboratory, where doctors open clogged arteries in patients with STEMIs.

"We can use this data to make people better aware of the risks and provide positive encouragement and assistance," he said.

The increased risk among smokers likely arises because smoking affects the plasticity of arteries and what happens inside them, said Dr. Umesh Khot, who is vice chair of cardiovascular medicine at the Cleveland Clinic in Ohio.

"The harms of smoking in terms of heart attacks of patients who smoke will happen a lot sooner than people think," said Khot, who wasn't involved with the new study.

He said it's never to late to quit smoking to reap some health benefits.

"For this type of heart attack known as STEMI, the risk drops off very fast," he told Reuters Health.

In an editorial accompanying the new study, Dr. Yaron Arbel of Tel Aviv Medical Center in Israel called for society to play a more active role in preventing and treating smoking habits in the general population through medical, legislative, commercial and educational efforts.

"Without all these efforts, we will not reduce the risks associated with smoking," he wrote.