The life expectancy for patients with HIV has increased by more than 13 years since the late 1990s thanks to advancements in anti-retroviral therapy, according to a new study published Friday.

Researchers from University of Alabama and other institutions around the world published their study in the British medical journal The Lancet.

Improved survival has led to a nearly 40 percent drop in AIDS deaths among 43,355 HIV-positive study participants in Europe and North America, bolstering the call for improved anti-HIV efforts worldwide, the authors said.

The authors looked at changes in life expectancy and mortality among the 43,355 HIV patients taking a cocktail of drugs called combination anti-retroviral therapy (cART).

“Since their introduction in 1996 cART regimens have become more effective, better tolerated and easier to follow,” said Michael Mugavero, a co-author on the study.

The study found cART yielded a 13.8-year life-expectancy increase — from 36.1 years in study participants who began therapy during the 1996-1999 period to 49.9 years in participants who began therapy during the 2003-2005 period.

Despite the good results, the study found life expectancy for HIV patients is far lower on average than the general population, which includes all those with other chronic illnesses. For example, an HIV-positive patient starting cART at age 20 will live to 63, about 20 years shorter than the average life span of non-infected adults.

With nearly half of all patients diagnosed with advanced HIV infection, the life expectancy benefits of cART are not fully realized, said the authors. Improved AIDS testing and increased access to care is needed, they said.