We’ve known for some time that smoking leads to an estimated 480,000 deaths a year in the United States from more than 20 diseases, including 12 types of cancer. New research supported by the American Cancer Society suggests that five other diseases that hadn’t been previously linked to smoking could cause an additional 60,000 deaths per year.
Researchers came to these conclusions on the basis of information from studies including data on nearly one million smokers who were followed for 10 years. When the investigators determined the number and causes of deaths associated with smoking in the study participants, they saw that the illnesses known to be linked to smoking accounted for only 83 percent of those deaths. Further investigation showed that the smokers were twice as likely to die of kidney failure, increased risks of infection, respiratory disease (other than chronic obstructive pulmonary disease, COPD), and a type of heart disease in which high blood pressure leads to heart failure. In addition, the team found that smokers were six times more likely than non-smokers to die of intestinal ischemia, a disease due to slowed or blocked blood flow to the intestines and deaths from breast and prostate cancer among smokers, but concluded that more research would be needed to confirm a connection.
We know that smoking can weaken the immune system, which may explain the deaths due to infections. It can also contribute to diabetes, high blood pressure and arterial disease, all of which can increase the risk of kidney failure. And the combination of the lung damage smoking causes and the increased risk of infection may explain the excess deaths among smokers due to respiratory problems newly associated with the habit.
This study doesn’t necessarily prove that smoking causes the five additional diseases that led to excess deaths among the study’s smokers. Instead, it showed an association between smoking and these deaths. To prove cause and effect, you would have to do a prospective study randomly assigning some people to smoke and others not to smoke – an impossible task, since it would be unethical to require anyone to smoke. The best we can do is compare rates of disease and deaths among smokers and non-smokers.
The only good news here is that the risks of the diseases newly connected with smokers appear to decline over time among those who quit.
For the record, the diseases smoking was known to cause before this study include cancers of the esophagus, stomach, colon, liver, pancreas, larynx, lung, bladder, kidney, cervix, lip and oral cavity, as well as acute myeloid leukemia, diabetes, heart disease, stroke, atherosclerosis, aortic aneurysm, other arterial diseases, chronic lung disease, pneumonia, influenza and tuberculosis. Earlier research has also revealed that smokers die, on average, more than a decade before non-smokers and are more than 20 times more likely to die of lung cancer.
Andrew Weil, M.D.
Brian D. Carter and Eric J. Jacobs et al, “Smoking and Mortality — Beyond Established Causes.” New England Journal of Medicine DOI: 10.1056/NEJMsa1407211