No one would argue that living a long time after receiving an HIV diagnosis is a good thing.

"I feel fabulous," says Carlton Smith, who was diagnosed with HIV 25 years ago. He is on the cusp of 50, "but I don't look like it," he is quick to say.

But what lies ahead for people like Carlton, diagnosed with HIV decades ago? They are living far beyond what anyone predicted when the HIV epidemic hit the United States in the 1980s.

By the year 2015, more than 50 percent of Americans living with HIV will be older than 50. As the availability of anti-iretroviral medications continues to expand, the rest of the world will not be far behind. But researchers are only beginning to understand how HIV and its treatment affects those living with HIV as they age.

Not that HIV hasn't always been a complicated disease for patients and their doctors to manage.

"Before aging was an issue, [HIV] care was complicated by multi-drug regimens [as well as] co-infections" and "major socioeconomic issues, including stigma, addiction, incarceration, homelessness and undernutrition," said Dr. Amy Justice, a professor of medicine and public health at Yale University. "Now we add to that mix chronic, noninfectious disease," she said at this week's International AIDS Conference.

According to a study released Thursday, among people over age 45, those with HIV are more likely to have more chronic diseases, such as high blood pressure, diabetes and cancer.

"Longer duration of being HIV-infected or exposed to [anti-retroviral therapy] were also associated with a higher prevalence of these chronic diseases," said Dr. Judith Schouten of the Academic Medical Center in Amsterdam and lead author of the study. Further, these diseases tended to occur five years earlier among patients with HIV than among those without HIV.

Take Carlton, for example. He also has diabetes. He takes four pills every day for HIV, and several more for diabetes. He takes his HIV pills in the morning in his diabetes pills in the evening. He has a doctor for his HIV, and another for his diabetes. This is working well for him, and he rarely forgets his pills.

But what happens if he develops other diseases requiring medication, such as high blood pressure, which runs in his family? Will he need another doctor? More pills?

As doctors look toward the treatment of a population aging with HIV, "we need to think about the limits of the silos of care we have created," says Justice, and focus instead on treating the whole patient, not just their different diseases.

But the interaction between chronic HIV and aging is only part of the issue. Older people also comprise 10 percent of new HIV infection in the U.S. And while many people might believe that older people aren't at risk for contracting HIV through sex, Ron Swanda, a 66-year-old longtime Washington, D.C., resident, has a simple message for the country: "Seniors are sexual."

He's right. More than 80 percent of men and more than 60 percent of women over 50 report having had sex in the last year in the U.S.

And older people have unique risks -- both behavioral and biological -- for acquiring new HIV infection. Men over age 50 are six times less likely to use condoms than their younger counterparts. And older women have thinner vaginal walls, which likely increases the risk of HIV transmission, according to Justice.

"I'm not saying that every grandma needs to be tested," said Swanda, who is a prominent activist for seniors and has been HIV-positive for more than 30 years. "But I want the country to do more to educate seniors about HIV and to test those at highest risk."