Smoking at an early age, particularly before turning 20, can lead to significant health issues in the future, regardless of whether you quit smoking for many years.

A study conducted by Seoul National University Hospital in South Korea analyzed data from over 9.2 million adults to explore the connection between the age individuals begin smoking and their risk of experiencing heart attacks or strokes as they age.

While the relationship between smoking and cardiovascular disease is well-documented, there has been limited research into how the age at which someone starts smoking impacts these health risks.

The findings, published in the medical journal Nature, involved 9,295,979 Korean adults who participated in health screenings in 2009.

Importantly, none of the participants showed signs of heart disease or had suffered a stroke before the study, and approximately 3.7 million of them were smokers.

Among these smokers, nearly 25% began smoking before the age of 20, with 2% starting even earlier, before the age of 15.

The researchers then looked at data to see who had suffered a heart attack, a stroke, or died from any cause. 

They also built up a bigger health picture for each person by estimating how much they smoked over their lifetime (packs per year), their age, sex, weight, blood pressure and cholesterol levels, if they had diabetes, if they drank alcohol and how regularly they exercised. 

Starting to smoke before the age of 20 carried serious risks for long term health 

Exploring the trends, the highest risks were seen in people who started smoking before age 20 and smoked heavily, which was defined has smoking more than 20 packs of cigarettes a year. 

Even people who had once smoked heavily but quit remained at higher risk.  

When they were compared with non-smokers, this group had more than double the risk of heart attack, and around 80 per cent higher risk of stroke. 

They were also at a much higher risk of dying during the follow-up period of up to 9.3 years. 

The heavy smokers who started young were worse off than the heavy smokers who didn’t start until adulthood (defined as 20 and over), but the people who started smoking before their fifteenth birthday were at the highest risk of stroke, heart attack, overall cardiovascular disease risk and death.

The risks remained high even after adjustments were made for how much they had smoked in total – i.e. if they had started young but also quit soon after. 

This led the researchers to conclude that when it comes to smoking cigarettes, the earlier someone started, the more damage each additional cigarette did over time. 

They argued that this might be because young blood vessels may be more vulnerable to damage and because damage to the arteries – a major cause of cardiovascular disease – can begin in childhood. 

Starting to smoke before the age of 20 was found to increase your risk of heart attack and stroke

Early smoking can also trigger long-term inflammation, affect cholesterol levels and how the blood clots, and cause stronger nicotine addiction. 

People who start smoking earlier were also more likely to drink more alcohol, exercise less and eat more processed foods. 

However, the because the study was observational, and taken from a one-time questionnaire, the results cannot be regarded as causational. 

Lead author Jung Hun Koh said that they hope the research will increase the amount of anti-smoking information aimed at younger people. 

They said: ‘Early initiation of smoking may imply the possibility of stronger addiction to the harmful social behaviour. 

‘In line with these findings, our analysis supports age- and intensity-dependent effects of smoking on the onset of cardiovascular diseases.

‘Moreover, we showed that smoking initiation in adolescence and in early adulthood both significantly elevate the risks of cardiovascular and mortality compared to starting smoking at age 30 or above.’ 

The Korean study comes just months after US researchers released a paper claiming that having a couple of cigarettes can lead to seriously detrimental health implications, even years after giving up. 

Researchers from Johns Hopkins Ciccarone Center for Prevention of Cardiovascular Disease in Baltimore, US, looked at data from 22 separate studies which followed a total of 330,000 people for close to two decades, 19.9 years. 

The team, lead by Dr. Michael Blaha, Professor of Cardiology and Epidemiology, documented more than 125,000 deaths and 54,000 cardiovascular events, such as heart attacks, strokes and heart failure. 

He said: ‘This is one of the largest studies of cigarette smoking to date using the highest quality data in the cardiovascular epidemiology literature. 

After crunching the numbers, they concluded that even very low-intensity smoking—which they defined as between two to five cigarettes per day—was associated with a 50 per cent higher risk of heart failure and a 60 per cent higher risk of death from any cause, compared to never smoking.

The study, published in journal PLOS Medicine, also found that a person’s risk of suffering a cardiovascular event dropped most substantially in the first decade after quitting smoking, with the risk continuing to decrease over time. 

But even thirty years after smoking their last cigarette, ex-smokers still had a higher risk of a cardiovascular illness when compared to those who never smoked.

Dr Blaha said that the research, which looked at the under represented demographic of ‘low-intensity’ smokers, showed that when it comes to giving up cigarettes, it’s a case of the sooner the better.