While it is already known that smoking increases the risk of suffering a major heart attack, a new study has found that this risk is much higher in women, especially those under the age of 50.

However, the good news is that smokers can reduce this risk to that of a never smoker in as little as one month after quitting the habit.

Heart disease is the world's biggest killer, including in Ireland. One of the most life-threatening forms of the disease is acute ST segment elevation myocardial infarction (STEMI), which is also known as a major heart attack. It is caused by a complete blockage of one of the main coronary arteries.

Smoking is a known risk factor for heart disease and previous studies have found that the habit causes almost 50% of all STEMI cases. However until now, it was not known how these risks differed between genders and age groups.

UK researchers decided to investigate this further. They looked at all STEMI cases (3,343) which occurred in a part of the UK between 2009 and 2014.

They found that smoking increased the risk of STEMI in all patients, regardless of gender or age. However, the risk was higher in females in all age groups when compared to males.

The highest risk among both men and women was in those aged 18-49, i.e. younger smokers, but again it was highest overall among women.

In fact, women in this age group were 13 times more likely to suffer a major heart attack compared to their non-smoking females peers. Men in this age group were eight times more likely to suffer a major heart attack than their male peers.

The researchers suggested a number of reasons why smoking may pose a higher STEMI risk for women, including that the habit may reduce levels of serum oestrogens. Oestrogens are known to protect against hardening of the arteries (atherosclerosis), but oestrogens are inhibited in female smokers.

However, the researchers also found that quitting smoking significantly reduces the risk of suffering a major heart attack.

"Our study found that smoking cessation, regardless of age or gender, reduces STEMI risk to that of a never smoker, possibly within a month. Patients who smoke merit encouragement to give up their habit, and this study adds quantitative evidence to the massive benefits of doing so," said the study's lead author, Dr Ever Grech, of the South Yorkshire Cardiothoracic Centre in Sheffield.

Details of these findings are published in the Journal of the American College of Cardiology.