The life expectancy of HIV patients has increased by 15 years since 1996, research by the University of Bristol has found.

Between 1996 and 2008, the average life expectancy of a 20-year-old infected with HIV rose from 30 to 46 years.

The improvements were likely to be a result of better antiretroviral therapy, more effective drugs and a general upward trend in UK life expectancy, the researchers said.

But they warned that early diagnosis and timely treatment were important factors in prolonging HIV patients' lives.

Starting antiretroviral therapy later than guidelines suggest could see patients losing up to 15 years of life, found the research, which was published on bmj.com.

And women with HIV also had a higher life expectancy than men with the disease, said the research team, led by Dr Margaret May of the University of Bristol's school of social and community medicine.

While men with HIV lived up to 40 years on average, women could expect to live until 50.

The study was an "urgent call" to raise awareness of the efficacy of HIV treatments, said Elena Losina, a senior scientist in Boston, in an accompanying editorial.

"This should increase rates of routine HIV screening, with timely linkage to care and uninterrupted treatment," said Ms Losina. "As these factors improve, the full benefits of treatment for all HIV-infected people can be realised."