One unexpected finding from a 2000 Kenyan study comparing breast and formula feeding was that breastfeeding poses a significant risk to maternal health. After 24 months, the maternal mortality rate in breastfeeding mothers was 11%, compared to 4% in the formula feeding arm. Infant mortality was strongly dependent on maternal mortality: infants whose mother died within the period of follow-up were eight times more likely to die subsequently than children whose mother survived. It should be noted that the women in this study were not receiving ART.^[1]

The researchers suggested that the demands of breastfeeding in HIV-infected mothers might accelerate the progression to HIV-related death. However, this does not accord with studies examining exclusive breastfeeding, which have not found higher death rates in breastfeeding women. Furthermore, prospective studies in Tanzania and Zambia found no evidence that breastfeeding was detrimental to the health of HIV-positive mothers.^[2][3]

The investigators wrote that recent studies have found that breastfeeding may not deplete a woman's energy reserves to the extent previously thought, and that a woman’s metabolic efficiency is improved during breastfeeding. They suggest that the association found between disease progression and breastfeeding in the Kenyan study could have been because it was observational in nature and failed to include adequate controls.

A 2005 meta-analysis has found no differences in mortality between HIV-positive mothers who ever breastfed compared to those who never did after 18 months. However, amongst the women who did start breastfeeding, the study found a lower risk of death among those who were still breastfeeding after 18 months. This is probably due to the fact that the women who are able to breastfeed for longer are the women who are healthier, rather than mortality being affected directly by the mother's choice of feeding method.^[4]

This question was looked at again in a study published in 2007. Nearly 300 women were enrolled in the study during pregnancy, given short-course AZT, and had their HIV-1 RNA levels and CD4 counts measured at baseline and every three months up to 24 months. Comparisons were made between the nearly 100 women who formula-fed and the nearly 200 women who breastfed.^[5]

Although decreased CD4 cell counts and BMI were associated with breastfeeding, HIV-1 RNA and mortality were not. The investigators concluded that there is a limited adverse impact of breastfeeding on a mother's health.