People infected with the AIDS virus who take multivitamins every day have a slightly slower progression of their illness, researchers are reporting today.

The findings will be most useful in the developing world, where an effort is underway to treat millions of HIV-infected people and vitamins could be an easily implemented first step.

The effect is not dramatic but is probably enough to warrant a recommendation that people infected with HIV take vitamins if their diet is potentially deficient, some experts said.

Supplements "might buy time to allow people to go longer before they develop symptoms that require antiretroviral treatment," said Lynne Mofenson, chief of AIDS activities at the National Institute of Child Health and Human Development. The institute paid for the study, whose results appear in today's New England Journal of Medicine.

The beneficial vitamins were in the B family, as well as vitamins C and E. Curiously, vitamin A -- which has huge health benefits in undernourished children -- was of no help, and was possibly harmful, in HIV-infected adults.

The new information comes from a study in the east African nation of Tanzania that began in 1995. About 1,000 pregnant women who were infected with HIV agreed to participate in an experiment to determine whether vitamin supplements could reduce mother-to-child transmission of the virus. Pregnancy increases the body's demand for vitamins, and many of the women were marginally nourished to begin with.

They were randomly assigned to take vitamin A, multivitamins with vitamin A, multivitamins alone or a placebo. The vitamin doses were six to 10 times the U.S. government's recommended daily dietary intake.

The study found that multivitamins alone decreased by about 40 percent a baby's chance of dying soon after birth -- mostly by reducing prematurity and low birth weight -- but the multivitamins did not cut the chance of acquiring HIV during birth or through breast-feeding. Vitamin A, however, increased the risk of acquiring HIV, and its use in the study was stopped when this became clear. Those findings were reported several years ago.

The women in the study continued taking supplements after they delivered and were observed until the summer of 2003 -- an average of about six years for the survivors.

Over the whole period, 25 percent of the women taking multivitamins progressed to late-stage AIDS or died, compared with 31 percent of those taking the placebo. This means that for every 100 women taking multivitamins for six years, the lives or health of six would have been preserved, compared with 100 women not taking vitamins.

Those numbers, however, do not fully reflect the benefit of multivitamins, said Wafaie W. Fawzi, a researcher at the Harvard School of Public Health, who headed the study.

For example, supplements (minus vitamin A) reduced a woman's risk of progressing to moderate AIDS, or of developing oral ulcers and painful swallowing, by 50 percent. Supplements raised a person's CD4-cell count -- a key measure of immune status -- by 48 cells per milliliter of blood, and slightly lowered the amount of HIV circulating in the blood.

In all, the effects of multivitamins were comparable to what was achieved by taking AZT alone in studies done during the 1980s when that was the only antiretroviral drug available.

It is not yet known whether multivitamins have an additional benefit for people already on optimal three-drug therapy, or whether multivitamins are beneficial in populations in which there is little nutritional deficiency.