HIV-positive mothers are less likely to pass on the infection to their babies if they breast-feed them for more than four months, a new study suggested.

The World Health Organization recommends all mothers, regardless of their HIV status, to exclusively breast-feed their babies for the first six months.

The study included nearly 1,000 HIV-positive women from Lusaka in Zambia. The study participants were then divided into two groups; with one weaning infants early and the second breast-feeding for more than four months.

Researchers found that HIV concentrations in the mothers' milk at 4.5 months were higher when the infants stopped breast-feeding, when compared with mothers who continued to exclusively breast-feed. Also, passing on HIV was less likely in mothers who exclusively breast-fed their babies.

"Our results support continuation of maternal antiretroviral drug interventions over the full duration of time when any breast milk exposures may occur after planned weaning," the researchers wrote.

An earlier research said that exclusive breast feeding by women who were infected with HIV does not reduce the progression of AIDS or other types of illnesses in infants.

A team of researchers had recently isolated antibodies in mother's milk that can protect the infant from being affected by HIV. Their study was published in the journal PLOS One.

The current study is published in the journal Science Translational Medicine.