Men and women who smoke as few as 1–4 cigarettes daily have a significantly increased risk of dying from ischemic heart disease and from all causes, according to a very large prospective study by Kjell Bjartveit, M.D., of the National Health Screening Service in Oslo, and a colleague.
Furthermore, the study, which followed 23,521 men and 19,201 women for more than 10 years, determined that women who are light smokers have an increased risk of lung cancer (Tobacco Control 2005;14:315–20).
After controlling for age, systolic blood pressure, total serum cholesterol, serum triglycerides, physical activity, body mass index, and height, the investigators calculated that light smokers had about a 50% increased risk of dying from all causes, compared with nonsmokers—a statistically significant increase in risk.
There was a clear dose-response relationship between daily cigarette consumption and adverse health outcomes. For example, men who smoked 20–24 cigarettes daily—not light smokers—had more than three times the risk of dying from all causes than nonsmokers.
Previous studies demonstrated similar dose-response curves, but in most, the lowest consumption group was set at 1–9 or 1–15 cigarettes daily. This allowed the Norwegian tobacco industry to suggest that there was a threshold level of smoking for which there were no health risks.
Participants in the study, who were residents of Oslo or one of three rural counties in Norway, were 35–49 years old when they were enrolled, between 1972 and 1978.
The investigators concluded that policymakers and health educators should emphasize more strongly that light smokers are endangering their health.