Study shows links between smoking bans, reduced risk of heart disease
University of Louisville researcher and director of the Diabetes and Obesity Center, Aruni Bhatnagar, Ph.D., was part of a national Institute of Medicine panel that reported on Oct. 15 that smoking bans are effective at reducing the risk of heart attacks and heart disease associated with exposure to secondhand smoke.
The report also demonstrated that breathing secondhand smoke increases nonsmokers' risk for heart problems, even in brief exposures. UofL Today talked to Bhatnagar about the study and its findings.
You were part of an Institute of Medicine committee examining the effectiveness of smoking bans - what was the committee charged to do?
The committee was asked to review the scientific evidence supporting the link between exposure to secondhand smoke and adverse cardiovascular events like heart attacks. We were asked not only to look at the effectiveness of smoking bans, but also to examine evidence of how secondhand smoke affects the development of heart disease.
The bans actually offered a natural experiment to look at the connection between exposure to secondhand smoke and the number of heart-related incidents in a community, before and after the bans were implemented. What happens to the rate of heart disease in a community when we withdraw the exposure to secondhand smoke? So we reviewed the scientific evidence linking secondhand smoke exposure to heart attacks.
What kinds of resources did the committee use to draw its conclusions?
We looked at 14 epidemiological studies published on smoking bans. In addition, we also looked at peer- reviewed data on animal models and human models showing the effects of secondhand smoke on different aspects of cardiovascular function and we examined reports on responses to secondhand smoke using models of heart disease that demonstrated the effects of the specific chemicals in tobacco smoke on cardiovascular health.
What did you find out about the effectiveness of smoking bans on heart health?
One of the conclusions the committee drew was that smoking bans do work because of the consistently positive nature of the studies showing a reduction in cardiovascular events and cardiovascular mortality in populations where bans had been implemented. This evidence provided a compelling argument that smoking bans do work.
But the main charge to the committee was to figure out if there was a possibility that exposure to tobacco smoke could induce a cardiovascular event, and we found circumstantial evidence for this. We wondered - if someone was exposed for 30 minutes, could that possibly trigger a heart attack? We did not have any direct data; even from the animal data there was only suggestive evidence that that might be possible, especially for patients in advanced stages of heart disease.
It's important to remember that heart disease doesn't develop overnight, but being exposed to secondhand smoke repeatedly over many years has a cumulative effect.
Give us some numbers - how much does the implementation of smoking bans reduce the risk of heart attacks?
There were variable numbers in terms of effect size and it varied from four to 40 percent but on average it was about 14 percent. Smoking bans could reduce the number of heart-related events by 14 percent. Again, there is a cumulative effect. If there has been no smoke exposure in a community for six to eight years, the effects of the ban on heart health seem to be the largest.
One interesting thing about heart disease is that you can measure changes in heart disease rates after just a few years. You can't do that with cancer because the risk doesn't go away that quickly. After 10 years of not smoking, the risk for lung cancer persists but risk for heart disease is back to normal. So we saw that risk of heart events was rapidly reversed, after say three to five years, where smoking bans were in effect.
People often think of smoking as it relates to lung cancer. Tell us about the link to heart problems.
Smoking affects the heart in many ways. It is a very strong signal to increase the blood-clotting mechanism. It increases the chances for abnormal rhythms, increases the accumulation of plaques in the arteries, and it could increase the chance of having a plaque rupture that could lead to a heart attack.
There was study by the California EPA that found that about 7000 deaths from lung cancer could be attributed secondhand smoke, but, in contrast, 40,000 heart deaths could be attributed to secondhand smoke. The other startling fact was that it seemed that very low levels of secondhand smoke exposure could cause heart problems, so the effects of heart disease start early.
What should members of the public as well as those considering smoking bans do with this information?
The entirety of the evidence suggests that smoking bans are effective and they far outweigh the cost - inconvenience, loss of patronage. We looked at smoking bans in major cities and there hasn't been a decline in businesses in any industry. We reviewed bans from Scotland, Rome, New York and other places. This is the first time someone has objectively arrived at a conclusion that the implementation of these bans was worth the effort.
Are there people who are more at risk than others from secondhand smoke and what should they know?
The biggest risk factors for heart disease are age, gender, cholesterol, blood pressure, smoking and diabetes. You can predict about 90 percent of risk. If you have two risk factors, say diabetes or cholesterol, the risk increases significantly. So people who have more than one risk factor are particularly susceptible to the harm of secondhand smoke.
Do you have any examples of smoking bans working? For instance, is there a university somewhere that instituted a ban and then saw productivity increase or health care costs drop?
We looked at one study that compared two university towns, one of which had implemented a smoking ban and one of which had not. The investigators found there were fewer heart-related deaths in the town where there was a ban, and it is important for young people to remember that they are not immune. It's a cumulative exposure, and it seems to add up. If the university can lessen the exposure then it's a good thing.
You don't have to have overt clinical heart disease to be susceptible to this. In most people the lesions start early, even as early as teens and they continue throughout life, so anytime you are exposed it can favor the development of these plaques in your arteries and even lead to their rupture. Almost everyone has at least the beginnings of heart disease - young people have lesions, even in people as young as 19 years old. Therefore, avoiding exposure to secondhand smoke could be one of the most effective preventive strategies to avoid heart disease.