Responding to the Enstrom and Kabat Study on Secondhand Smoke

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November 2004

The tobacco industry has a long history of trying to cast doubt on the science of secondhand smoke. In its latest attempt, the industry has funded a new study, published in the British Medical Journal. The study, written by researchers funded by the tobacco industry, misrepresented data from the American Cancer Society (ACS), and used flawed methodology to come to the inaccurate conclusion that secondhand smoke does not cause an increased risk for lung cancer and heart disease. Don’t be fooled by Big Tobacco. Secondhand smoke kills.

“The study is fundamentally flawed.”

–British Medical Association1

The British Medical Journal published a study in its May 2003 issue entitled, “Environmental tobacco smoke and tobacco related mortality in a prospective study of Californians, 1960-1998,” which was authored by Dr. James E. Enstrom and Dr. Geoffrey C. Kabat. The study claimed that no causal relationship was found between secondhand smoke and tobacco-related mortality, after analyzing data from 35,351 adults over a period of thirty-eight years. As one might expect, the study generated an enormous amount of media attention. Speculation abounded that the unanimous conclusion of public health officials and medical practitioners, that secondhand smoke is hazardous to health, had been premature. Big Tobacco and its allies hailed the study as proof that the adverse health effects of secondhand smoke are greatly exaggerated. Under closer scrutiny, the inevitable was found to be true: the Enstrom and Kabat secondhand smoke study was largely funded by tobacco industry dollars, conducted by industry allies, and riddled with methodological errors.

Although the Enstrom and Kabat secondhand smoke study has now largely been discredited, the tobacco industry and its allies attempt to use the study to cast doubt upon the science of secondhand smoke. This document provides some basic information regarding the study, its funding, and its authors, and should help to counter any attempts to use the study to undermine the established body of research confirming the health hazards of secondhand smoke.

THE STUDY

“The editors believe that this opinion piece is full of speculative assumptions of doubtful scientific value. We could not judge the merits of your criticisms because your own data and methods were so inadequately described. I should add that your article contains pejorative comments that should have no place in responsible scientific discourse.”

—Letter from the Journal of the American Medical Association to James E. Enstrom2

The data and design of the Enstrom and Kabat secondhand smoke study has been widely criticized. Even the British Medical Association, the publisher of the journal that printed the study, described the research as being “fundamentally flawed.”3 The misuse of data and flawed methodology are two very significant faults in the study.

Enstrom and Kabat did not gather original data for their study. Instead, it drew on data from the ACS’s Cancer Prevention Study (CPS-I), and used only a small subset (approximately 10%) of the total CPS-I data. Researchers at ACS repeatedly warned Enstrom that the data from CPS-I could not be used to determine the health effects of secondhand smoke, and they spoke out against the study upon its release, stating that their data had been misused.4

The study used cohort methodology to look at the rate of mortality from heart disease and lung cancer in nonsmokers who were married to smokers, covering a time period from 1959 to 1998. A severe error in the study was the failure to establish a control group of nonsmokers who were unexposed to secondhand smoke. Other critical methodological flaws include not measuring for secondhand smoke exposure from any source other than the spouse, including workplace (where smoking was extremely prevalent at the time); not taking into account either spouse’s smoking status after 1972, though the study continued for 26 more years; and classifying the nonsmoking spouse as still exposed to secondhand smoke in that 26 year period, during which time the “smoking spouse” could have quit smoking or died, not to mention that they could have divorced or separated.

THE FUNDING

“A substantial research commitment on your part is necessary in order for me to effectively compete against the large mountain of epidemiologic data and opinions that already exist regarding the health effects of ETS and active smoking.”

-- Dr. James E. Enstrom to Philip Morris Research Center5

The Enstrom and Kabat secondhand smoke study was initially funded by a grant from the Tobacco Related Disease Research Program, an organization that manages funds generated by the Proposition 99 California state cigarette tax. After the program’s scientific, peer-review panel, denied continued funding for the project, Enstrom sought out financial support from other sources. In 1997, he submitted an application for,6 and ultimately received, $210,000 from Philip Morris and the Council on Tobacco Research (CTR)7,8,9, a front group created in 1954 by the tobacco companies to fund research on smoking and health.10 It became well known over the years for sponsoring flimsy scientific research that promoted tobacco industry positions.

THE AUTHORS

“For the past three years, I have done consulting and research on passive smoking for Jeffery L. Furr of Womble Carlyle on behalf of RJ Reynolds and Philip Morris.”

-- Dr. James Enstrom to the Center of Indoor Air Research11

CONCLUSION

Enstrom and Kabat’s substantial methodological flaws, combined with the tobacco industry’s funding of the study, and other studies supported by the tobacco industry, can help you to inoculate others against this misinformation. Over one hundred independently funded, peer-reviewed studies show that secondhand smoke exposure causes serious disease and death in nonsmokers. Don’t let this one study undermine the body of solid science that confirms the hazardous health effects of secondhand smoke exposure. For more information on Enstrom and Kabat or other studies that challenge the credible science of secondhand smoke, please contact us at (510) 841-3032 or at anr@no-smoke.org.

REFERENCES

  1. [n.a.], “BMA response to BMJ paper ‘effect of passive smoking on health’,” British Medical Association, May 16, 2003.
  2. Rennie, D. “[Letter from JAMA to James E. Enstrom re: published study.],” Philip Morris, August 23, 1996, Bates No. 2073788479. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/kiv85c00.
  3. [n.a.], “BMA response to BMJ paper ‘effect of passive smoking on health’,” British Medical Association, May 16, 2003.
  4. [n.a.], “American Cancer Society Condemns Tobacco Industry Study for Inaccurate Use of Data,” American Cancer Society, May 15, 2003.
  5. Enstrom, J., “Proposed Research on the Relationship of Low Levels of Active Smoking to Mortality,” Philip Morris, January 15, 1997, Bates No. 2075873003. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/dfk37d00.
  6. Ibid., 1997.
  7. Carchman, RA., “Principal Investigator @ D James E. Enstrom, PhD, MPH, Grant Title @D ‘Relationship of Low Levels of Active Smoking to Mortality’,” Philip Morris, January 30, 1998, Bates No. 2063654067. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/hyf67e00.
  8. CTR, “CHECK TRANSMITTAL FORM GRANT NUMBER: 3333AR2,” Council for Tobacco Research, February 11, 1998, Bates No. 40001768. Accessed on November 14, 2004. Download at http://legacy.library.ucsf.edu/tid/dlx89c00.
  9. CTR, “CHECK TRANSMITTAL FORM GRANT NUMBER:333AR2,” Council for Tobacco Research, July 11, 1997, Bates No. 40001771. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/ilx89c00.
  10. Glantz, SA.; Slade, J.; Bero, L.; Hanauer, P.; Barnes, D., The Cigarette Papers (University of California Press: Berkeley, Los Angeles, London) 1996.
  11. Enstrom, J., “Proposed Research on Passive Smoking,” Brown and Williamson, July 15, 1996, Bates No. 566944402. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/tww91d00.
  12. Enstrom, J. “[Letter re: funding for tobacco study within Mormon community.],” Council for Tobacco Research, June 3, 1975, Bates No. 50207891-7892. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/ldi79c00.
  13. Enstrom, J.; Kabat, G. “Environmental tobacco smoke and tobacco related mortality in a prospective study of Californians, 1960-1998,” British Medical Journal, Volume 326, May 17, 2003.
  14. [n.a.], “WSA / INBIFO Project Milestone Status Report 000519 – 000615,” Philip Morris, June 22, 2000, Bates No. 2505591306/1310. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/mqb19c00.
  15. Nelson, BL, “[Letter re: speaking opportunity.],” Philip Morris, May 18, 2000, Bates No. 2073736520. Accessed on November 17, 2004. Download at http://legacy.library.ucsf.edu/tid/vrx85c00.
  16. [n.a.], “[Search in American Legacy Tobacco Documents Library re: Kabat.],” http://legacy.library.ucsf.edu, November 17, 2004.