Smoking just two cigarettes a day can wreak havoc on your heart, study shows

New research dismantles the long-held belief that smoking less means less harm. 

Scientists now say the body suffers significant cardiovascular damage from even low levels of smoking.

Researchers from the American Heart Association's Tobacco Regulation and Addiction Center analyzed data from 22 long-term health studies involving more than 320,000 adults.

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The findings, published in PLOS Medicine, show that smoking even a few cigarettes a day sharply raises the risk of heart disease and early death and that quitting entirely is the only way to reverse those risks.

In the study, adults were divided into never smokers, current smokers and former smokers, according to a press release.

Researchers looked at how much people smoked, measuring in "pack-years" and cigarettes per day. For former smokers, they looked at how long it had been since they quit.

The team then compared those patterns to multiple health outcomes, including heart attack, stroke, heart failure, atrial fibrillation and overall death rates.

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Current smokers had more than double the risk of dying from any cause compared to people who never smoked. 

Those who smoked just two to five cigarettes a day had double the chance of developing heart disease.

"Smoking even two to five cigarettes a day can more than double your risk of any type of heart disease and raise your risk of death from any cause by 60% compared to people who never smoked," the association stated in the release.

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The study also found that health risks "immediately decrease" after someone stops smoking, and continue to substantially drop over time.

Within 10 years, former smokers saw major improvements, and after about 20 years, they had more than an 80% lower risk than current smokers, but the damage takes a long time to fully fade.

According to the AHA, "while quitting smoking greatly reduced smoking-related health risks in the first 10 years, it may take 30 years or more for health risks among people who previously smoked to be on par with people who never smoked."

Researchers say the lesson from this study is that the only safe level of smoking is not smoking at all.

"Lower-intensity smoking is associated with cardiovascular risk, and the primary public health message for current smokers should be early cessation, rather than reducing the amount of smoking," they wrote.

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The authors noted a few limitations, namely that smoking habits were self-reported at the start of each study.

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"The stigma attached to smoking could lead to underreporting of current smoking status, particularly among women, affecting the accuracy of the data," the study states.

The researchers also did not include data on e-cigarettes or other tobacco products.