According to research from the Netherlands, babies who were nourished with nothing other than breast milk for over four months had less respiratory and gastrointestinal disease. When babies were exclusively breastfed during the first six months benefitted from even more protection against infection through the next six months as well.
"Breast milk not only provides all the nutrients a baby needs but moms are also passing along antibodies,which help protect their little ones from infections that cause diarrhea and pneumonia, the two leading causes of child mortality worldwide according to the World Health Organization. More than 1 million child deaths could be avoided each year if more babies were exclusively breastfed during the first six months of life according to the WHO website."
The World Health Organization, the American Academy of Pediatrics, the American College of Obstetricians and Gynecologists, the American Academy of Family Physicians, and the Centers for Disease Control and Prevention all agree that babies should be exclusively breastfed for the first six months.
http://pagingdrgupta.blogs.cnn.com/2010/06/21/new-study-supports-exclusive-breastfeeding-for-first-six-months/?utm_source