Smoking cigarettes explained almost 3 of 4 myocardial infarctions (heart attacks) among HIV-positive people, compared with only 1 of 4 heart attacks in the general population, according to results of a nationwide study in Denmark.1 The researchers estimated that 42% of heart attacks in people with HIV people might be avoided if all HIV-positive smokers quit.
People with HIV infection have higher myocardial infarction rates than people without HIV. Several factors could contribute to higher heart attack risk in people with HIV, including high rates of traditional risk factors (like smoking) and HIV infection itself. Researchers are still trying to sort out the relative impact of various risk factors on heart attacks in HIV-positive people.
Smoking is among the strongest contributors to heart attack risk, and people with HIV tend to smoke more than people without HIV. A recent nationwide study in the United States calculated that 42% of people with HIV smoke, compared with 21% of the general population.2 Research from other countries confirms smoking rates 2 to 3 times higher in people with than without HIV.
An earlier study by Danish researchers linked smoking to a 4.4-fold higher risk of death from any cause in people with HIV, and with a 5.3-fold higher risk of non-AIDS death.3 A previous study of 17,995 antiretroviral-treated people in the United States and Europe found that a 35-year-old smoker would lose 8 years of life because of smoking, compared with 6 years lost because of HIV infection.4
A Danish team conducted this new study to learn more about how smoking affects heart attack risk in people with HIV compared with HIV-negative people, and to estimate the proportion of heart attacks that might be avoided if HIV-positive people never smoked or if smokers quit.
The researchers began by selecting all HIV-positive people in Denmark from the nationwide Danish HIV Cohort Study, which began in January 1995. They did not include people who got infected with HIV by injecting drugs or people who already had a heart attack. For each HIV-positive person, the investigators selected 4 people from the ongoing Copenhagen General Population Study. They matched these 4 general-population controls to the HIV-positive person by gender and age (within 5 years). No one in the general-population group had a previous heart attack.
Then the researchers checked the Danish National Hospital Registry to see which people in either group had a heart attack. From records of the Danish HIV Cohort Study and the Copenhagen General Population Study, the investigators classified each person as a current smoker, a previous smoker, or a never smoker. For each person the study period started on (1) January 1, 1999, (2) the date of HIV diagnosis, (3) the date when smoking status could be determined, (4) the date at 40 years of age, or (5) the date of immigration to Denmark, whichever was most recent.
The researchers used standard statistical methods to compare the new heart attack rate (incidence) in people with versus without HIV. They adjusted this analysis to account for several heart attack risk factors. They also figured the population-attributable fraction of heart attacks, that is, the proportion of heart attacks that could be explained by smoking (see note 5).
The study involved 3233 HIV-positive people matched by age and gender to 12,932 people in the general population. Four of every 5 people studied were men, and median age stood around 45 years. Among HIV-positive-people, 47% were current smokers, 19% previous smokers, and 34% never smokers. In the general-population group, 20% were current smokers, 34% previous smokers, and 46% never-smokers.
During the study period 95 people with HIV (2.9%) and 125 without HIV (1.0%) had a heart attack. The new heart attack rate (incidence) was 5.20 per 1000 person-years in the HIV group and 1.98 per 1000 person-years in the general population. (An incidence of 5.2 per 1000 person-years means about 5 of every 1000 people had a heart attack every year.) Statistical analysis that accounted for other heart attack risk factors determined that HIV-positive people had more than a doubled risk of heart attack compared with the general population (Figure 1).
Figure 1. HIV infection independently more than doubled the risk of a heart attack in a large Danish study (far left bar). HIV-positive current smokers had a 6-fold higher heart attack risk than HIV-positive people who never smoked (second bar from left), while HIV-negative current smokers had only a 2.22-fold higher heart attack risk than HIV-negative people who never smoked (middle bar). HIV-positive previous smokers had a 2.64-fold higher heart attack risk than HIV-positive people who never smoked (fourth bar from left), while HIV-negative previous smokers had essentially the same heart attack risk as HIV-negative people who never smoked (last bar).
Next the researchers calculated heart attack rates in three groups -- current smokers, previous smokers, and never smokers (Figure 2). Current smokers had the highest heart attack rate (8.33 per 1000 person-years in people with HIV and 3.57 per 1000 in the general population). The heart attack rate was lower in previous smokers (4.50 per 1000 in people with HIV and 1.87 per 1000 in the general population). And the heart attack rate was lowest in people who never smoked (1.43 per 1000 in people with HIV and 1.29 per 1000 in the general population).
Figure 2. In both HIV-positive people and the general population of Denmark, current smokers had the highest heart attack rate (left two bars), previous smokers had a lower rate (middle two bars), and never smokers had the lowest rate (right two bars). But HIV-positive people had a higher heart attack rate than people without HIV in each of the three groups -- current, previous, and never smokers.
Statistical analysis that accounted for other heart attack risk factors determined that people with HIV who currently smoked had a 6-fold higher heart attack risk than HIV-positive people who never smoked (Figure 1). HIV-positive people who smoked previously had almost a 3-fold higher risk than HIV-positive people who never smoked. In comparison, HIV-negative people who currently smoked had about a 2-fold higher heart attack risk than HIV-negative people who never smoked, and HIV-negative people who smoked previously had a heart attack risk similar to that of HIV-negative people who never smoked (Figure 1).
Among people with HIV, 72% of heart attacks could be attributed to smoking (the population-attributable fraction). This means that if none of these HIV-positive people ever smoked, 72% of heart attacks might be prevented. In contrast, only 24% of heart attacks in the general population could be attributed to smoking. Finally, the researchers calculated that if all current smokers with HIV stopped smoking, 42% of heart attacks might be avoided. If all current smokers in the general population stopped smoking, 21% of heart attacks might be avoided.
This large comparison of people with HIV and a general-population group matched by age and gender made several important findings:
Together these findings confirm that smoking has a profound impact on the health and survival of people with HIV. In fact, the results indicate that smoking may harm people with HIV more than HIV-negative people.
For all of these reasons, HIV-positive smokers should find a way to quit, and nonsmokers should never start. This study found a much lower heart attack risk in former HIV-positive smokers than in current smokers. And if all the HIV-positive people in this study quit smoking, more than 40% of heart attacks might be prevented.
Some people -- even long-time smokers -- can make up their mind to quit and never have another cigarette. For most people, though, quitting can be tough because nicotine is addictive. But smokers who want to quit should realize that many smokers do manage to kick the habit. The United States, for example, has more former smokers than current smokers.6
If you want to quit smoking, your HIV clinician can help you find a way that works for you. Sometimes nicotine replacement strategies help people stop; others quit with the help of medications like Chantix or Champix.7 "Decision Tree Guides Selection of Smoke-Ending Medication for People With HIV" in this issue of HIV Treatment Alerts outlines a study showing success with a decision tree to help HIV clinicians select the right smoke-ending medication for each person.8 Positively Smoke Free, an internet program, has helped HIV-positive people stop.9
Remember that quitting smoking prevents not only heart attacks, but also lung cancer and many other cancers, stroke and peripheral vascular disease, and chronic obstructive pulmonary disease.10
|Smoking Lowers Life Expectancy More Than HIV Itself|
|Smoking Almost Triples Heart Attack Risk in Those Living With HIV|
|Decision Tree Guides Selection of Smoke-Ending Medication for People With HIV|
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