http://www.who.int/bulletin/volumes/91/6/12-109363.pdf
WHO Bulletin Breastfeeding policy - a globally comparative analysis
Concludes:
"A greater percentage of women practise exclusive breastfeeding in countries where laws guarantee breastfeeding breaks at work. If these findings are confirmed in longitudinal studies, health outcomes could be improved by passing legislation on breastfeeding breaks in countries that do not yet ensure the right to breastfeed."