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Smoking more harmful than HIV for people taking effective treatment, US study suggests
Keith Alcorn, 2016-11-08 06:50:00

Smoking has the potential to shorten the life of a person taking HIV treatment by an average of six years, and is far more harmful to the life expectancy of people living with HIV than well-managed HIV infection itself, a US study reports this month in the Journal of Infectious Diseases.

The study found that stopping smoking improved life expectancy, with the greatest gain in life expectancy seen when smoking was stopped by the age of 40.

Dr Rochelle Walensky of the Massachusetts General Hospital Division of Infectious Diseases, senior author of the study, said, "It is time to recognise that smoking is now the primary killer of people with HIV who are receiving treatment."

Smoking reduces life expectancy through cardiovascular disease (stroke and heart attack), cancers and chronic obstructive pulmonary disease (emphysema). In the United States general population the prevalence of smoking has declined from 42% in 1965 to 17% in 2014, but a 2015 study estimated that 40% of people living with HIV in the United States still smoke.

To investigate the impact of smoking on life expectancy among people living with HIV and on treatment in the United States, researchers at Massachusetts General Hospital developed a model of the impact of smoking and smoking cessation in this population.

The study used data from the North American AIDS Cohort Collaboration (NA-ACCORD) to create a model of the population living with HIV in the United States and receiving care. The researchers then modelled the impact of persistent smoking, stopping smoking or never smoking on the life expectancy of people living with HIV, assuming that everyone started treatment with a highly effective antiretroviral regimen on entry to care at the age of 40. The age of 40 was chosen because NACCORD found that the median age at entry to HIV care in its participating cohorts was 43 years.

The model assumed that people would enter care with a mean CD4 cell count of 360 cells/mm3 and then compared the effect of entering care at the age of 40 or at 50, so as to model the interaction between later HIV infection and smoking.

Estimates of the impact of smoking on life expectancy were derived from US general population mortality figures, and also assumed that the risk of death would begin to diminish for those who gave up smoking depending on the age at which they stopped. So, for people who gave up at the age of 35, the risk of death had fallen to the same level as the risk of death for those who never smoked by the age of 40, but for those who didn’t give up until the age of 55, the risk of death remained 70% higher than for never-smokers. This adjustment reflects the accumulated damage caused by smoking.

The study also adjusted for sex – the risk of death was persistently lower for women who smoked, at all ages – and for higher mortality in HIV exposure categories other than men who have sex with men.

The model produced from these inputs showed that male smokers who entered care at the age of 40, and who kept smoking, had an estimated life expectancy of 65.2 years. Former smokers who quit at the age of 40 would live to the age of 70.9 years and those who never smoked to the age of 71.9 years. Women who entered care at the age of 40, and who kept smoking had an estimated life expectancy of 69.9 years. Women who had stopped smoking would live to 72.7 years and those who never smoked would live to 74.4 years.

This compares with the World Health Organization’s estimate of an overall life expectancy for the general population in the United States of 79.3 years (76.9 for men and 81.6 for women). Life expectancy is two to three years higher in Western Europe, Japan and Australasia.

The model finds that the loss of life expectancy due to smoking for people living with HIV is probably greater than the loss of life expectancy due to HIV infection. Indeed, one study in the United Kingdom has found that people with HIV who have a good response to treatment may have life expectancy that matches the general population.

The model found that stopping smoking at 40 resulted in a gain in life expectancy of 5.7 years for men and 4.6 years for women.

Entering care at 50 years – indicating later infection with HIV – was associated with longer life expectancy among smokers but also a less pronounced difference in life expectancy between smokers and former smokers. Male smokers who entered HIV care could expect to live to 69.9 years, those who quit to 73.4 years and those who never smoked to 76.5 years. Women who continued to smoke after entering care at the age of 50 could expect to live to 72.4 years, those who quit to 75.7 years and those who never smoked to 78.8 years.

The study also found that stopping smoking at the age of 40 was associated with greater gains in life expectancy for both men and women than starting antiretroviral treatment at a CD4 count above 500 compared to late initiation.

Based on previous cohort studies, the researchers estimated that 40% of people living with HIV in the United States are current smokers and 20% ex-smokers. They calculated that if 10% - 25% of current smokers with HIV aged 30-64 were to stop smoking, between 106,000 and 265,000 extra years of life would be gained.

The study authors point out that a much lower proportion of people living with HIV quit smoking compared to the rest of the population, and that “smoking cessation should be a major priority in HIV carer programs.”

An accompanying editorial commentary by Keri Althoff of Bloomberg School of Public Health, Johns Hopkins University, Baltimore, discusses some of the challenges of improving smoking cessation rates in HIV care, and potential solutions.

A combination of pharmacological treatment and counselling to assess readiness to quit has proved successful, but cessation rates are still “disheartening”, she writes. Integrating smoking cessation into a comorbidities prevention package of care requires a degree of sensitivity: patients may be overwhelmed by interventions to address mental health issues, weight and smoking on entry to care, and interventions need to be carefully staged.

Retention in care could be adversely affected if patients face too many demands at once. “Implementing the intervention among patients who have achieved stability during ART may be preferable, as patients will have demonstrated success with an intervention and may be more ready to tackle another health issue,” she suggests.

Recording of tobacco use in the electronic medical record should ideally prompt automatic linkage to local resources for smoking cessation outside the HIV clinic, reducing barriers to accessing these services.