Aging people in the United States have active sex lives, unrestrained by age-related sexual problems affecting around half of them, according to a major nationwide report published Thursday.

"A majority of older Americans are sexually active and view intimacy as an important part of life, despite a high rate of 'bothersome' sexual problems," the National Institutes of Health (NIH) said in a report on the new study.

The research found that sexual appetite declines only slightly between the ages of 50 and 70, with many men and women practicing vaginal intercourse, oral sex and masturbation well into their 70s and 80s.

Researchers at the University of Chicago surveyed 3,005 people aged 57 to 85, said the NIH, part of the US Department of Health, in what experts said was the first study of its kind to focus on the growing aging population in America.

The study "suggests a previously uncharacterized vitality and interest in sexuality that carries well into advanced age," said Richard Suzman of the National Institute on Aging (NIA) which took part in the study.

Half of those surveyed up to the age of 75 admitted to having oral sex, said the summary report released here Wednesday on the study, which is published in Thursday's issue of The New England Journal of Medicine.

More than half of men and a quarter of women admitted masturbating.

Nearly three-quarters of those aged 57 to 64 said they were sexually active. The figure dropped to just over half of those in the 65 to 74 age range, and a quarter of those aged 75 to 85.

Sexual activity was more common among older men than among older women.

The survey sheds light on the impact of physical health on people's sex lives, including sexual problems related to conditions such as arthritis, diabetes and hypertension, the report summary said. Overall health, it found, was more important than age in boosting a person's sex life.

The research may also help promote health education efforts to prevent sexually transmitted disease in older people.

"Sexual activity among older adults poses risks for new cases of HIV, as approximately 15 percent of newly diagnosed HIV infections are among Americans over age 50," the summary said.

About half of the sexually active older adults reported at least one "bothersome" sexual problem. More than a third of active men said they had erectile difficulties, and 43 percent of women reported "low desire."

American men spend more than a billion dollars each year on medications to improve their sexual function, the researchers said, with 14 percent of those surveyed taking medicine to boost their performance.

"People are living longer," said Stacy Tessler Lindau of the University of Chicago, a physician who led the study.

"Many people have higher expectations for what aging should be like, and we spend billions on treating erectile problems. Yet we have no baseline data on sexuality in later life," she said.

"These data will give people a sense of whether what they're experiencing is typical."

The only other comparable study on sex was published in 1999 and covered Americans age 18-59.

A study by South African scientists said Wednesday there was no evidence that foods such as garlic and beetroot were a substitute for AIDS medicine, disputing claims by the country's health minister.

The report — confirming what experts worldwide have said — was likely to increase pressure on the minister, who has been ridiculed for promoting olive oil, garlic, lemon and the African potato for people with AIDS and for questioning the effectiveness of anti-retroviral drugs.

Health Minister Manto Tshabalala-Msimang is also under fire because of the dismissal of her deputy and over newspaper allegations her liver transplant may have been needed because of alcohol abuse. Recent news reports also said she was banned from Botswana for 10 years in the 1970s after being accused of theft at a hospital.

"The panel has concluded that no food, no component made from food, and no food supplement has been identified in any credible study as an effective alternative to appropriate medication," said professor Barry Mendelow, one of the authors of the 300-page study by the Academy of Science of South Africa.

The 15-member panel said healthy eating does appear to help slow the progression of AIDS and tuberculosis. But it cautioned that there was little reliable evidence about the influence of nutrition on the diseases.

"This contrasts dramatically with the huge cloud of often acrimonious controversy that hangs over the subject and has become a source of widespread concern in, and about, the government, both within and outside the country," the panel said.

Tshabalala-Msimang's spokesman could not be reached for comment on the report.

Controversy about the country's AIDS policy has raged for years, with critics accusing the government of doing too little to slow the epidemic, which affects an estimated 5.4 million South Africans. An estimated 900 people die each day of the disease in South Africa, and some 1,400 are newly infected. A report last year warned that only half the 15-year-olds now alive would live to celebrate their 60th birthdays.

In April, the government finalized a plan to halve the number of new infections by 2011 and extend treatment and care to 80 percent of those in need. But AIDS activists voiced concern about the commitment to those targets after the dismissal this month of Deputy Health Minister Nozizwe Madlala-Routledge, who was widely credited with revitalizing the AIDS campaign.

President Thabo Mbeki said he axed the deputy for not working as part of a team. But Madlala-Routledge and other critics say it was because she had differences with her 66-year-old boss, a close friend of Mbeki's from the anti-apartheid struggle.

Tshabalala-Msimang has attracted titles such as "Dr. Garlic" and "Dr. Beetroot" for her ideas on AIDS treatment.

"Raw garlic and a skin of the lemon — not only do they give you a beautiful face and skin, but they also protect you from disease," she told a news conference in 2005. "All I am bombarded about is anti-retrovirals, anti-retrovirals. There are other things we can be assisted in doing to respond to HIV/AIDS in this country."

The Academy of Science disagreed.

"One of our most important findings has been that nutrition is important for general health, but is not sufficient to contain either the HIV/AIDS or the tuberculosis epidemic," said panel member Dr. Dan Ncayiyana, editor of the South African Medical Journal. "We need a well-nourished nation. But a well-fed population on its own is not going to resist HIV/AIDS without anti-retroviral drugs."

The report said there might be unknown and unrecognized substances in edible and medicinal plants with beneficial effects. "However, until these suggested remedies have been proven to do more good than harm the panel cannot support their use," it said.

The opposition Democratic Alliance renewed calls for Mbeki to dismiss the health minister. It said the report was "yet another piece of evidence to contradict the minister's highly public and extremely damaging opinion that good nutrition is of equivalent value to anti-retrovirals in treating AIDS."