Importance of light smoking and inhalation habits on risk of myocardial infarction and all cause mortality. A 22 year follow up of 12 149 men and women in The Copenhagen City Heart Study

STUDY OBJECTIVE: To determine risk of myocardial infarction (MI) and all cause mortality associated with light smoking and inhalation habits in men and women.

DESIGN: Prospective cohort study with follow up of MI and all cause mortality through record linkage.

SETTING: The Copenhagen City Heart Study, a cardiovascular study based on a sample of the general population established in 1976.

PARTICIPANTS: 6505 women and 5644 men followed up until 1998 for first MI and for death from all causes. Main results: During follow up 476 women and 872 men suffered a MI whereas 2305 women and 2883 men died. After adjusting for major cardiovascular risk factors there was a dose-response relation between smoking with and without inhaling and both MI and all cause mortality. Among inhaling smokers significantly increased risks were found in women at a consumption of only 3-5 grams of tobacco per day with relative risks (RR) of MI and all cause mortality of 2.14 (95% CI 1.11 to 4.13) and 1.86 (95% CI 1.37 to 2.51), respectively. In men increased risks were seen when smoking 6-9 grams per day with RR of MI and all cause mortality of 2.10 (95% CI 1.40 to 3.14) and 1.76 (95% CI 1.39 to 2.23), respectively. Risks were also increased in non-inhaling smokers, although in men only significantly so for all cause mortality. After adjusting for inhalation and quantity smoked, cigarette smokers had a higher risk of all cause mortality (RR 1.16 (95% CI 1.07 to 1.26)) but not of MI (RR 1.11 (95% CI 0.95 to 1.30)). The RR associated with smoking were significantly higher in women than in men for both MI and all cause mortality.

CONCLUSIONS: Smoking as little as 3-5 grams of tobacco per day or not inhaling the smoke was shown to carry a significantly increased risk of developing MI and of all cause mortality with higher RR found in women than in men. The study emphasises the importance of recognising that even very limited tobacco consumption has detrimental health effects.