Is there a threshold value for daily cigarette consumption that must be exceeded before serious health consequences occur?

Numerous population studies have reported on a strong dose–response relationship between cigarette consumption and severe diseases. In most studies, however, the lowest consumption group was set at 1–9 or 1–15 cigarettes per day.

One may argue that smokers in these groups clustered close to the upper limit of this consumption span, and that a threshold value might be found on a lower level.

Only a few prospective studies have reported on the health consequences of smoking fewer than five cigarettes per day.1–3

However the studies revealed that adjusted relative risk (95% confidence interval) in smokers of 1–4 cigarettes per day, with never smokers as reference, of dying from ischaemic heart disease was 2.74 (2.07 to 3.61) in men and 2.94 (1.75 to 4.95) in women.The corresponding figures for all cancer were 1.08 (0.78 to 1.49) and 1.14 (0.84 to 1.55), for lung cancer 2.79 (0.94 to 8.28) and 5.03 (1.81 to 13.98), and for any cause 1.57 (1.33 to 1.85) and 1.47 (1.19 to 1.82).

In both sexes, smoking 1–4 cigarettes per day was associated with a significantly higher risk of dying from ischaemic heart disease and from all causes, and from lung cancer in women. Smokingcontrol policymakers and health educators should emphasise more strongly that light smokers also endanger their health.