Sharp Increase in Mortality Risk from Smoking

June 1, 1997

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.

BETHESDA, Md--A new analysis of data from five large studies of smokingand health, which involved a total of nearly 2.75 million participants,reveals that mortality risks associated with cigarette smoking have surgedover the last four decades, particularly for women.

The new report, released by the National Cancer Institute (NCI), attributesthe sharp increase to a greater lifetime dose of cigarette smoke experiencedby smokers in the later studies. And its findings suggest that enormoushealth benefits would accrue from preventing smoking among adolescents.

The monograph presents newly analyzed data from the five studies. Thenumber of people in each study ranged from nearly 61,000 to just under1.2 million. Follow-up varied from 6 to 26 years, and a total of nearly490,000 deaths were available for analysis.

The report found that the risks for all smoking-related deaths, includingthose from lung and other cancers, heart disease, stroke, and chronic obstructivelung disease (COPD), have risen, with women smokers registering the sharpestrise.

"The findings are extremely troubling for anyone concerned withpublic health," said NCI director Richard D. Klausner, MD. "Especiallytroubling is the large increase in relative risks observed among womenfor cancer of the lung and other smoking-related cancer sites."

Two of the epidemiologic efforts--The US Veterans study and the AmericanCancer Society's (ACS) Cancer Prevention Study I (CPS I)--began in 1954and 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 pointedout the sharp increase in cancer risks. The two studies used nearly identicaldesigns and methodologies; each included more than 1 million people.

Among men, for example, the risk of a smoker developing lung canceressentially doubled among those participating in CPS II, compared withdata from CPS I, rising from 11.9 to 23.2 times that of a nonsmoker. Therelative risk in women, however, jumped nearly five times, going from 2.7in 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 formale smokers and from 1.8 to 2.6 for female smokers. The relative riskfor coronary heart disease among male smokers went from 1.7 in CPS I to2.3 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 smokingmachines indicated that tar and nicotine yields from cigarettes were decreasing.According to the NCI, the average tar level in a cigarette has droppednearly 70% since 1955, and average nicotine levels have fallen by almostthe same percentage. However, smokers today generally smoke more and begansmoking earlier than those in the studies that started in the 1950s.

"Smokers in the newer studies consumed more cigarettes per daythan smokers followed in the earlier studies, and much of the differencebetween the two sets of risks disappears when duration of smoking historyand number of cigarettes smoked per day are held constant," said DavidM. Burns, MD, of the University of California, San Diego, the monograph'ssenior editor.

Dr. Burns noted that a solid and substantial body of research demonstratesthat the smokers of today smoke their cigarettes more intensely than smokersdid 40 years ago.

"They draw larger puffs and inhale the smoke deeper into the lungs,"Dr. Burns said. "However," he added, "the impact of thischange 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 "importantcornerstones for documenting smoking-induced diseases." And, he added,they reveal the enormous benefit that can be derived from successful programsthat prevent smoking among adolescents and that get adults to stop.