A total of ten studies were identified that assessed whether smoking was associated with more rapid progression to AIDS. These were published between 1990 and 1999, and all took place in wealthy nations – Canada, the United Kingdom, Ireland, Norway and the United States – prior to the widespread availability of potent antiretroviral therapy.

It should be noted that in February 2005 - when the authors undertook their systematic review - the association between smoking and HIV disease progression was unclear. However, studies published before and since this review took place strongly suggest that smoking has both a direct and indirect impact on the life expectancy of HIV-positive individuals.

Six studies assessed whether smoking was associated with an increased risk of acquiring HIV infection. Five studies – published between 1990 and 1996 in Haiti, the United States, Rwanda and Thailand – found that smoking was associated with somewhere between a doubling to a quadrupling increased risk of acquiring HIV infection in unadjusted analysis. Analyses adjusted for some confounding factors, however, revised the estimate to somewhere between a 1.6-fold and 3.5-fold increased risk.

However, the only truly prospective study to examine this association - from the United States' Multicentre AIDS Cohort Study (MACS) group and published in 1991 - concluded that smoking was not associated with an increased risk of acquiring HIV infection. This nested case-control study of 644 gay and bisexual men found that the adjusted risk was 1.22-fold, with a 95% confidence interval ranging between 0.99-1.50.

The reviewers' assessment that smoking may increase the risk of HIV infection is provocative, particularly since this association has previously received little attention, possibly because so far no plausible biological mechanism adequately explains the increased risk, but also because all the studies published so far have not ruled out all the possible confounding factors. For example, smokers may be more likely to have a more cavalier attitude towards risk tha non-smokers, and this may affect sexual risk-taking - something that has not been measured in the studies that were reviewed.

Furber AS et al. Is smoking tobacco an independent risk factor for HIV infection and progression to AIDS? A systematic review. Sex Transm Infect. Published online 21st August 2006.

1. A full review of this study and prior studies that also suggest an increased risk of various cancers, cardiovascular disease, lung disease and poorer oral health in HIV-positive smokers compared to HIV-positive non-smokers is available in the latest (August/September 2006) issue of NAM's monthly newsletter AIDS Treatment Update (ATU 159). There is also information on smoking cessation support for HIV-positive individuals. ATU is available free to all HIV-positive individuals; professionals can subscribe to ATU alone or as part of various NAM subscription packages. For details please email us at: info@nam.org.uk, or call +44 (0)20 7840 0050.

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