B Vitamins, along with vitamins C and E, may also reduce the symptoms of the disease, including fatigue, nausea, vomiting, difficulty swallowing, and mouth and stomach problems, the study found.

But the test of 1,078 pregnant women in Tanzania also found that vitamin A seems to counteract the benefits of giving the supplements.

About 40 million people are infected with HIV, the Aids virus, and less than 8 percent of the people who should be getting treatments actually are.

"Multivitamin supplements delay the progression of HIV disease and provide an effective, low-cost means of delaying the initiation of antiretroviral therapy in HIV-infected women," said the research team, led by Wafaie Fawzi of the Harvard School of Public Health.

The effect of the multivitamin was strongest during the first two years, according to the Fawzi team.

Although the benefits of multivitamin therapy, which cost about $15 per year, were statistically significant, they were not dramatic.

The chance of dying or developing an advanced case of HIV was 24.7 percent among the vitamin recipients, compared to 31.3 percent among women who received placebo tablets instead.

The researchers said the recipients of the vitamin supplements tended to have higher levels of disease-fighting cells and lower levels of HIV virus particles in the blood.

But in cases where vitamin A had been added to the treatment, the benefit faded and those women fared about as well as the volunteers getting placebos.