May 5, 2017
Compared with HIV-positive 40-year-olds who never smoked, those who do smoke could lose more than 6 years of life as a result.1 The statistical analysis that provided that estimate also figured that HIV-positive 40-year-olds who quit smoking when they start HIV care could save 5 or 6 years of life. HIV-positive smokers 50 or 60 years old also gain life years if they quit.
Smoking remains the leading preventable cause of death in the United States, according to the Centers for Disease Control and Prevention (CDC).2 Although smoking shortens life by up to 10 years in the general U.S. population, some of those lost years can be "regained" if people quit smoking.3 The CDC determined that 42% of HIV-positive adults in the United States smoke, compared with 20% of U.S. adults without HIV.4 Another 20% of adults with HIV are former smokers,4 a finding indicating that a sizeable proportion of people with HIV do quit.
U.S. researchers performed this analysis to estimate how many years of life HIV-positive people lose if they smoke -- and how many years of life they regain if they quit.
The study relied on a mathematical model that has been used successfully in people with HIV. A mathematical model plugs data into mathematical formulas to predict real-life outcomes. For example, models have a good record in making accurate weather forecasts. Health researchers are refining the ability of models to predict health outcomes -- like life expectancy.
The models assume that everyone starts antiretroviral therapy as soon as they begin care for HIV, as U.S. treatment guidelines now recommend. For each individual created by the model, the analysis forecasts the course of their health and eventual death by considering the impact of several real-world factors. Those factors include CD4 count, viral load, AIDS-related diseases, adherence to antiretroviral therapy (taking all pills on time), and keeping medical appointments. For all health-related factors in smokers and nonsmokers -- and in people with and without HIV -- the researchers used actual findings they collected from previous studies.
The mathematical models aimed to estimate how long HIV-positive people entering care would survive if they never smoked, if they smoked and continued smoking, or if they smoked then quit smoking when they started HIV care. The analysis figured these survival rates for men and women, and for people who stopped smoking 5 or 10 years after they entered HIV care.
The researchers also used models to compare life years lost from smoking in HIV-negative people versus HIV-positive people. And in the HIV-positive group, they compared life years lost from smoking with life years lost from HIV infection. The research team performed this last analysis in (1) HIV-positive people with less than perfect adherence (antiretroviral pill taking) and less than perfect medical appointment keeping, and (2) in HIV-positive people with perfect antiretroviral adherence and appointment keeping.
Finally, mathematical models figured how many life years would be gained if HIV-positive smokers quit smoking when they started HIV care according to (1) sex, (2) age when HIV care began, and (3) CD4 count when HIV care began.
The researchers estimated that almost 250,000 HIV-positive 30- to 64-year-olds in care in the United States smoke. The model projected that a 40-year-old man starting HIV care and continuing to smoke could expect to live to age 65.2 (Figure 1). A man who quit smoking when starting HIV care at age 40 could expect to live to age 70.9 (5.7 years longer than the man who did not quit smoking). And a man who never smoked and started HIV care at age 40 could expect to live to 71.9 (6.7 years longer than the man who did not quit smoking).
Figure 1. A mathematical projection study estimated that HIV-positive people who start antiretroviral therapy at age 40 and who smoke can expect to live to age 65.2 (men) or age 68.1 (women) if they do not stop smoking. In contrast, 40-year-olds who quit when they enter HIV care at age 40 can expect to live to age 70.9 (men) or 72.7 (women). And 40-year-olds who never smoked can expect to live to age 71.9 (men) or 74.4 (women). (Credit: Teresa B. Southwell)
A woman who started HIV care at age 40 and did not quit smoking could expect to live to age 68.1 (Figure 1). But if that woman quit smoking when she started HIV care she could expect to live to 72.7 (4.6 years longer than if she did not quit smoking). And if she never smoked she could expect to live to 74.4 (6.3 years longer than a smoker who did not quit).
The researchers figured that a 40-year-old HIV-negative man loses 10.7 years of life from smoking, while a 40-yearold HIV-negative woman loses 10.6 years from smoking. Among 40-year-old current smokers with HIV and less than perfect pill-taking adherence and appointment keeping, the model projected that men lose 6.7 years of life from smoking and 6.9 years from HIV infection. HIV-positive 40-year-old women who smoke lose 6.3 years of life from smoking and 8.3 years from HIV.
The model makes different predictions for 40-year-old men and women with perfect pill-taking adherence and appointment keeping (Figure 2): Men in this group could expect to lose 8.6 years from smoking but only 3.5 years from HIV. And women could expect to lose 8.2 years from smoking but only 4.3 years from HIV. In other words, HIV-positive people who take their antiretrovirals on time and keep all their medical appointments are less likely to die from HIV, and smoking has a much greater impact on their life expectancy than HIV itself.
Figure 2. HIV-negative 40-year-old men and women can expect to lose more than 10 years of life from smoking, according to mathematical analysis projections. Among HIV-positive 40-year-olds who take all their antiretrovirals on time and keep all medical appointments, the model projects that smoking subtracts 8.6 years of life in men and 8.2 years in women. In contrast, HIV subtracts only 3.5 years in men and 4.3 years in women who take all their HIV pills and keep appointments. (Credit: Teresa B. Southwell)
The model also figured that smokers who start HIV care but do not quit smoking for another 5 or 10 years still add to their life expectancy when they do quit. For example, a man who smokes and starts HIV care at age 40 gains 5.7 years of life if he stops smoking at the same time he starts HIV care, 3.3 years of life if he quits smoking 5 years after starting HIV care, and 2.9 years if he quits smoking 10 years after starting HIV care. Women smokers who start HIV care at age 40 gain 4.6 years if they quit smoking immediately upon starting care, 3.1 years if they quit 5 years after starting care, and 2.8 years if they quit 10 years after starting care.
Quitting smoking adds life years not only for people 40 years old when starting HIV care, but also for people 50 or 60 when starting care. For example, the model projected that among men who start HIV care with a CD4 count of 300, those 50 years old can expect to gain 3.6 years of life by quitting smoking and those 60 years old can expect to gain 2.6 years of life. For women who start care with a CD4 count of 300, those 50 years old can expect to gain 3.3 years of life from quitting and those 60 years old can expect to gain 2.4 years.
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