Smoking as few as three to five cigarettes a day can significantly increase the risk of heart attack, according to research published in the current issue of the Journal of Epidemiology and Community Health. The study also found that women are much more susceptible than men to the detrimental effects of tobacco.
The findings are based on a population sample of over 12,000 men and women who took part in the Copenhagen City Heart Study, which began in 1976. It monitored the participants, all aged 20 years or older at the start of the study, up to 1998.
After adjusting for major cardiovascular disease risk factors, including cholesterol levels, lifestyle, family history, weight and diabetes, the results showed a strong and increasing link between the amount smoked and the risk of heart attack and death from other causes.
Compared with non-smokers, men doubled their risk of heart attack by inhaling the smoke of six to nine cigarettes a day. Among women, the detrimental effects were evident at lower levels of tobacco use. Inhaling the smoke of just three to five cigarettes a day doubled a woman's chance of heart attack.
Many smokers believe that as long as they do not inhale the smoke, smoking is not hazardous. The study is one of the first to try to establish the risk associated with this practice.
Although based on the participants' self-reported behaviour rather that an objective measurement of smoke inhalation, the authors report an association between cardiovascular risk and not inhaling while smoking. Among men, smoking but not inhaling six to nine cigarettes a day increased the risk of heart attack by 13 per cent. However, a woman smoking the same number but not inhaling, increased her risk by almost 60 per cent.
According to the authors, women's greater susceptibility to the harmful effects of tobacco is thought to be because they are more prone to lung disease than men. In addition, smoking affects a woman's oestrogen balance, so the protective effect of the female hormone against cardiovascular disease is compromised.
Commenting on the results, Dr Fenton Howell, chairman of ASH Ireland, said: "It [the study\] underscores the fact that many people die from heart disease as a result of smoking. In addition, people believe that 'light smoking' - less than 15 cigarettes a day - is not harmful or only causes minimal harm. Unfortunately, this study shows that it takes only a small amount of smoking . . . to cause a significant impact on health."