BETHESDA, Md--A new analysis of data from five large studies of smoking and health, which involved a total of nearly 2.75 million participants, reveals that mortality risks associated with cigarette smoking have surged over the last four decades, particularly for women.
The new report, released by the National Cancer Institute (NCI), attributes the sharp increase to a greater lifetime dose of cigarette smoke experienced by smokers in the later studies. And its findings suggest that enormous health benefits would accrue from preventing smoking among adolescents.
The monograph presents newly analyzed data from the five studies. The number of people in each study ranged from nearly 61,000 to just under 1.2 million. Follow-up varied from 6 to 26 years, and a total of nearly 490,000 deaths were available for analysis.
The report found that the risks for all smoking-related deaths, including those from lung and other cancers, heart disease, stroke, and chronic obstructive lung disease (COPD), have risen, with women smokers registering the sharpest rise.
"The findings are extremely troubling for anyone concerned with public health," said NCI director Richard D. Klausner, MD. "Especially troubling is the large increase in relative risks observed among women for cancer of the lung and other smoking-related cancer sites."
Two of the epidemiologic efforts--The US Veterans study and the American Cancer Society's (ACS) Cancer Prevention Study I (CPS I)--began in 1954 and 1959, respectively. The remaining three began about a generation later: the Nurses' Health Study (1976), Kaiser Perma-nente (1979), and CPS II (1982).
In their new analyses of CPS I and CPS II, ACS investigators pointed out the sharp increase in cancer risks. The two studies used nearly identical designs and methodologies; each included more than 1 million people.
Among men, for example, the risk of a smoker developing lung cancer essentially doubled among those participating in CPS II, compared with data from CPS I, rising from 11.9 to 23.2 times that of a nonsmoker. The relative risk in women, however, jumped nearly five times, going from 2.7 in CPS I to 12.8 in CPS II.
For all smoking related cancers--including larynx, oral cavity, esophagus, bladder, kidney, and pancreas--the relative risk rose from 2.7 to 3.5 for male smokers and from 1.8 to 2.6 for female smokers. The relative risk for coronary heart disease among male smokers went from 1.7 in CPS I to 2.3 in CPS II. For female smokers, it rose from 1.4 to 1.8.
Smoking More and Starting Earlier
The rise in mortality risk occurred at a time when tests using smoking machines indicated that tar and nicotine(Drug information on nicotine) yields from cigarettes were decreasing. According to the NCI, the average tar level in a cigarette has dropped nearly 70% since 1955, and average nicotine levels have fallen by almost the same percentage. However, smokers today generally smoke more and began smoking earlier than those in the studies that started in the 1950s.
"Smokers in the newer studies consumed more cigarettes per day than smokers followed in the earlier studies, and much of the difference between the two sets of risks disappears when duration of smoking history and number of cigarettes smoked per day are held constant," said David M. Burns, MD, of the University of California, San Diego, the monograph's senior editor.
Dr. Burns noted that a solid and substantial body of research demonstrates that the smokers of today smoke their cigarettes more intensely than smokers did 40 years ago.
"They draw larger puffs and inhale the smoke deeper into the lungs," Dr. Burns said. "However," he added, "the impact of this change on increased mortality risks remains unknown."
Donald Shopland, coordinator for NCI's Smoking and Tobacco Control Program, called the long-term, prospective studies analyzed in the monographs "important cornerstones for documenting smoking-induced diseases." And, he added, they reveal the enormous benefit that can be derived from successful programs that prevent smoking among adolescents and that get adults to stop.