Mortality risks of smoking and obesity.

Both smoking and obesity cause increased health problems, but it is unusual to find an analysis of their separate and combined effects in a single study. One such study was published by Dr Freedman and colleagues of the National Cancer Institute in 2006. They analyzed a nationwide, prospective mortality study of U.S. radiologic technologists (64,000 women and 18,000 men) who were recruited 1983-89 and followed up to 2002. As in many studies of obesity the main measure was the Body Mass Index (BMI) which is a measure of body fat based on height and weight that applies to both adult men and women. The “normal weight” BMI comprises the range of 18.5 to 24.8. For example, the upper boundary for “normal weight” for someone who is 5 feet 10 is 173 pounds (bmi=24.8), and a person of that height would be classified as obese at a weight of 209 pounds (bmi=30) and “very obese” at a weight of 244 pounds (bmi=35).

For women aged under 65 who never smoked, there was no excess risk of death due to being obese, but for those in the “very obese” range the mortality risk relative to normal weight people was 1.87 (ie increased by 87%). However, compared to a normal weight never smoker, the relative risk for a normal weight smoker was 2.22 (i.e. increased by 122%, I.e more than doubled). This shows that the mortality risk caused by smoking is greater even than the risk due to being “very obese”. In fact this means that for a normal weight individual, the excess mortality risk due to smoking is greater than the risks due to putting on over 70 pounds!

Of course the mortality risks are larger still (RR=5.2) for someone who is very obese AND smokes. The mortality risk patterns for men were similar to those of women

The mortality risks from circulatory diseases were particularly affected by smoking and BMI, with combined smoking and obesity producing a 6-11-fold increase in cardiovascular mortality risks.

Overall, the study found that, “in all gender/age groups, both obesity and smoking, particularly current smoking, contributed substantially to all-cause mortality, with 3.5- to 5-fold risks for very obese, current smokers compared to normal weight, never smokers. Current smoking was the predominant risk factor for cancer mortality. Combining obesity with current smoking increased circulatory disease mortality by 6- to 11-fold for people aged less than 65 years, compared to normal weight, never smokers. Obese former smokers (less than 65 years) had notably lower risks.”
The authors of the study concluded that:
“Obese smokers (aged less than 65 years) had strikingly high mortality risks, particularly from circulatory disease mortality.”
It is clear from this study that smoking poses much larger health risks than obesity, but that combining these risk factors produces marked increases in health risks. Smokers planning to quit, or ex-smokers who may have put on some weight should know that the health benefits of quitting smoking far outweigh the health risks of putting on a few pounds (e.g. 10 pounds).

Freedman DM, Sigurdson AJ, Rajaraman P, Doody MM, Linet MS, Ron E. The mortality risk of smoking and obesity combined. Am J Prev Med. 2006 Nov;31(5):355-62.
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About the Author

MA, MAppSci, PhD

Dr. Jonathan Foulds is an expert in the field of tobacco addiction.