Patients taking HIV drugs in Africa can expect to have a near-normal lifespan, although men are likelier to die far sooner than women, according to the biggest study of its kind, issued on Monday at the world conference on AIDS medicine.

Researchers at the University of British Columbia and the BC Centre for Excellence in HIV/AIDS in western Canada trawled through data for 22,315 people in Uganda aged at least 14 who had initiated antiretroviral therapy between 2000 and 2009.

They were measured against life expectancy in Uganda which is around 55 years, a figure that increases with age after the individual has cleared key milestones such as death in infancy or risk behaviour in adolescence.

Individuals in the study who were at the age of 20 when they began therapy were statistically likely to live an additional 26.7 years, and at the age of 35 another 27.9 years.

But this was the overall figure, and there were big differences between the sexes.

Twenty-year-old males on HIV drugs could look to an additional 19.1 years of life, but female counterparts another 30.6 years.

The gap was maintained at the age of 35, when an infected male under treatment could expect to live another 22 years but a woman could live 32.5 years more.

The suspected reason for this is that men tend to access care at a later stage of disease than women, when they are already badly infected by the human immunodeficiency virus (HIV).

Previous research has already established that earlier treatment leads to stronger health as the immune system, compromised by the AIDS pathogen, recovers.

The study, which was also published in the US journal Annals of Internal Medicine, is the biggest analysis of life expectancy south of the Sahara.

Although the probe only looked at data for Uganda, the authors say its basket of settings -- rural, semi-rural and urban -- and scant medical resources make it a snapshot for Africa as a whole.

"The substantial life expectancy afforded by widespread access to (antiretroviral drugs) underscores the fact that HIV diagnosis and treatment in resource-limited setting should no longer be considered a death sentence," said lead investigator Edward Mills in a press release.

"Instead, HIV-infected people should plan and prepare for a long and fulfilling life."

Georgetown University investigator Mark Dybul, who led the implementation of former US president George W. Bush's massive plan for AIDS help in the last decade, said the findings were "further evidence that the global investment in HIV and AIDS programming is clearly working."

The study is the latest in a series of inquiries into wider use of the drug "cocktail" that first emerged in 1996 and has become one of the greatest successes in the history of medicine.

AIDS has killed around 30 million people since it was recorded as a novel disease in 1981.

More than 34 million people were living with HIV, two-thirds of them in Africa, at the end of 2010, according to UNAIDS.

In poorer countries, 6.6 million badly-infected people have grasped the drug lifeline, a nearly 22-fold increase since 2001, but another nine million are still in need.